Synthesizer Build part-3: TRIANGLE TO SINEWAVE CONVERTER

This article has been re-written at 11-11-2020.

After I had finished the VCO I wanted to add a Sinewave option to it. The first design I had posted here was a bit sketchy so I now present a new layout here. This layout has been made using the schematic of the Thomas Henry CEM3340 Deluxe VCO, which has a sinewave output. Btw, you can find that schematic in the 'files' section of the 'Synth DIY for non engineers Facebook Group'.

This circuit needs the Triangle input wave to be +/-5 Volt peak-to-peak. You can input a Trianglewave of 0V to +10Vpp but then the input must first go through the 1µF electrolytic capacitor to take away the offset voltage. The Triangle to Sinewave converter will not work properly if you input a 0/+10Vpp Trianglewave without first filtering out the DC offset voltage.

I altered the feedback resistor (Rf on layout) from 10K to 15K to get the amplitude correct with the waveform standard of my synthesizer project which is 0 to +10Vpp. This had the effect that the +/-5V output got a negative offset voltage. What I should have done is change the other 10K that goes from the + input to ground into a 15K also, so everything is in balance again but I put a 1µF capacitor in series with the output of the +/-5Vpp sinewave. The negative pole of the electrolytic capacitor is facing the direction the signal is coming from because I had a negative offset voltage to deal with. Make sure you match the 10K resistors so they all have the same value and if you change the feedback resistor to a 15K make sure you change the other 10K to ground also. Match the transistors too. (Matching them on hfe is good enough). If after all that you still have an offset voltage on the output (unlikely) then you can put a 1µF cap in series with the +/-5V output.

The output amplitude on a dual 12V powersupply is +/-4.2Vpp or 0 to 9.4Vpp. For a dual 15V power supply it is +/-5Vpp or 0 to 10Vpp.

Here is the new stripboard layout. This converter offers a +/-5Vpp output and a 0/+10Vpp output. 

Here is the schematic drawing. I did not include any de-coupling capacitors but if you want to include them then just add two 100nF ceramic capacitors to the voltage rails as close to the chip as possible. One going from +15V to ground and the other from ground to -15V.

Here are two pictures from the oscilloscope. One without offset from the +/-5Vpp output and one with offset from the 0/+10Vpp output. If you look closely at the pictures you see that the scope is set to 2V per division and therefore that the amplitude of the sinewave is 8V. But now that I changed the feedback resistor Rf, that has changed to 10V (even a tiny bit over):

As you can see they are beautiful sinewaves and you can set the symmetry and distortion very accurately with the trimpots on the stripboard. 

It will be easy enough to mount this little stripboard on one of the M3 bolts used to mount the print of the 'Really Good VCO' and thus add a Sinewave output to that VCO. You can tap the Trianglewave straight from pin 10 of the AS3340 (or CEM3340) chip or from pin 12 of the TL074 quad opamp chip. I think that will be even easier. On those pins the Trianglewave is not yet given a +5V offset voltage so it is still +/-5Vpp and therefore doesn't need to go through the 1µF electrolytic capacitor on the layout of the Triangle- to Sinewave converter. 

Okay that's the new version of this article done. If you have any questions please put them in the comments below or on the EddyBergman Facebook Group page.

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Btw, all the comments below upto August 2020 refer to the original Tri- to Sinewave converter article and not to this one. So please disregard those comments.

Synthesizer Build part-2: THE VCO

A word in advance: this article deals with the first VCO I've ever built and is based on the datasheet schematic combined with the LookMumNoComputer lay-out for the CEM or AS3340 chip. I personally had great trouble getting this VCO tuned over a wide range of octaves.  I could also never get really deep notes from this design. I have since found a much better VCO design so if you want to build a simple but excellent working and tunable VCO on stripboard I refer you to Synthesizer Build part-18: A Really Good VCO design.

I'm keeping this article up for my own archive and as a warning for those just starting out not to build this VCO!!!

Here's the original text for the first VCO build:
After having constructed the power supply and the power bus system it is time to move on to the next step. The Voltage Controlled Oscillator. I'm not going to go into details as to how it works etc. There's plenty info online about that.  In order to make this a complete build, not just the circuit board I needed something to mount the knobs and in- and outputs on. So I ordered a sheet of Aluminium, 200 x 1000 X 1.5 mm and powder coated gray/black on one side. That is fantastic stuff to make panels out off and I highly recommend it. You can saw off panels of the right width using an electric jigsaw with a fine toothed metal saw. Make sure you guide the saw with a straight piece of wood or metal to get nice straight panels.

For my VCO I chose the AS3340 chip which is a complete 1 volt per Octave VCO in a chip. It's a clone of the CEM3340 which were used in the 80's in synths like the Prophet 5 the Roland SH101 and many others.
The VCO we're building here will have almost all the options that the AS3340 chip has to offer and those we didn't include are not worth having anyway ;)
The schematic I used is pretty much just the schematic that comes on the datasheet.

This is the one I used:

I used the layout made by Sam Battle, from LookMumNoComputer and did a few enhancements on it. (Look to the one on the right).

For one, his layout is meant for the CEM3340 which uses a 10K pulldown resistor on pin 4, the squarewave output. For the AS chip, that's supposed to be a 51K resistor although I'm reliably informed it doesn't make a blind bit of difference what you use here. There was also a mistake in his design, namely the 10K resistor in the bottom left near the TL072. It is switched in parallel with the 10K on pin 4 making the overall resistance 5K. Just leave the bottom 10 K resistor out.
The 10K trimmer potmeter at the top left of the 3340 needs to be a multiple turn potmeter so you can set it very accurately.

Sam's layout doesn't include the High Frequency Tracking but you really need to include it in your VCO. I first build it without and at first it seemed to work fine but after having completed the whole synthesizer I couldn't get really deep bass tones out of it. That is until I included the High Frequency Tracking. Seems a paradox that something meant for High Frequency adjustments can have so much influence on the bass notes but if you look at the schematics you can see that it pulls the CV voltage on pin 15 down to ground a bit through the 20K potmeter. I kept out the 360K resistor between +15V and CV input because that kicks the VCO into really high notes. I don't know why that resistor is there but it really screws up the frequencies. I left it out but maybe I should have experimented further with that resistor in place. Anyway...
The HF adjustment pot only adjusts about half a note over its full throw so when you first test it it might look as though it doesn't work but it does when you start tuning the higher octaves of the VCO.

Furthermore I gave the buffer for the triangle wave a gain of 2 by adding two 100K resistors to the TL072. That gets the level of the triangle output up to 10V peak-to-peak, in line with the output voltages of the other two waveforms. Btw, you can use any resistor value between 50K and 1M for this purpose as long as both resistors have the same value.

I also added the Positive and Negative Hard Sync options from the Digisound 80 Modular design so that's also available on this VCO.

Here is the layout that I drew and used:

So there we have it. It's become quite a comprehensive VCO with lots of options.
I added a 100K resistor to the +15V input of the Pulse Width Modulation potmeter to get it to work over the complete throw of the potmeter and I added a switch to have the ability to decouple it from the PW Control Voltage if you have PWM controlled by an LFO for instance. You don't have to decouple it but the option is there.

I tested the finished print and everything worked as expected but there was a funny quirck in the squarewave output. Below 1.35kHz there was a strange triangular wave ringing on the downward slope of the square-wave. Here's some pictures of that from my scope:

I opened a discussion about this in the Synth DIY Facebook Group and there were many suggestions but I still haven't figured out the cause. It's not a de-coupling issue anyway.
I suspect that leaving out the High Frequency Tracking I mentioned earlier may be the cause. (Note: I did some more tests and it turns out that it does have a big influence on this issue. Including HF Track with the 360K resistor to +15V almost gets rid of the problem but on low frequencies there still is a bit of ringing on the downward slope but not nearly as much as now.
But as I mentioned before, the 360K resistor really screws up the frequency response so it can not be included. I have heared that there might be batches of chips that have this fault, so it might be the chip. I don't know and don't really care because you don't hear it and everything works fine.

[Edit: In the second VCO I built and now use (see article 18) this ringing is still there but it is much less then in this design. The new VCO has at most 3 spikes in the downward slope of the squarewave. Anyway it has proven to be not a problem what so ever. You can't hear it and it doesn't affect the working of either VCO in any way.]

Although the connection is there in the layout, I did not use the Soft Sync input on my final build. I don't think I'll need it. I did use the FM input. You can connect a second VCO to that for instance.
Here's a look at the finished product, panel and all. The powder coated Aluminium was a great choise and looks so cool. It doesn't scratch easy at all, it's perfect for this project.

I'll explain what's on the panel.
We have the FM input at the top left. The big knob at the top is the Coarse Tune potmeter, below that on the left are the CV1 and CV2 inputs and on the right are the Triangle-, Ramp- or Sawtoothwave and below that the Squarewave outputs. ( I always put inputs on the left and outputs on the right.)
Then there are three inputs to the left of the blue knobs. Those are the Pulse Width Control Voltage input, the blue knob next to it controls its level. Underneath that are the Positive Hard Sync and Negative Hard Sync inputs. The bottom blue knob is the Manual Pulse Width control if you don't use a control voltage. The switch with the diode symbol let's you choose to put a diode in the external Pulse Width input line which de-couples it from the internal PWM control or to bypass that diode and get more range on the PWM control knob. [edit] I have since scrapped this idea and I took out the diode. The switch is now used to turn off or on the manual Pulse Width Modulation potmeter as described above. (It's not necessary but the switch was there so might aswel use it for something). I added one more output which isn't in this picture and that is a "CV out" function to connect the second VCO to the first one. It's simply switched in parallel with the CV-1 input.


Okay, that's it for this one. If you have questions or suggestions please write them in a comment. Next part will be about a filter, probably the Prophet One Low Pass filter.
Stay tuned!

Synthesizer Build part-1: SYMMETRICAL POWER SUPPLY (1,5A) with independent voltage adjustment.

The essential building block for our DIY synth. with outputs for +/- 15V, 12V and 5V at 1.2 Ampères.

Please scroll half way down the article to find the second version (which is modular in set-up) with stripboard layouts

WARNING, THIS PROJECT REQUIRES YOU TO WIRE UP A MAINS TRANSFORMER. BE VERY CAREFUL WHEN HANDLING MAINS POWER. IT CAN BE DEADLY AS YOU PROBABLY KNOW. IF IN DOUBT ASK AN EXPERT OR POST QUESTIONS IN THE FACEBOOK GROUP. DON'T TAKE CHANCES WITH MAINS ELECTRICITY!!

In Oktober 2019 I set myself the task of building my own synthesizer. I started by slowly buying in the components I was going to need, as my budget allowed (and that wasn't much ^__^).
The first thing I needed for this project was a symmetrical power supply to give me positive and negative voltages, because practically everything in a synthesizer runs on a dual powersupply.
I used the LM317 and LM337 for this project because they are easy to work with and fully protected inside against short circuits and over heating. The LM3XX series regulators can deliver up to 1,5 Ampères.
This is the schematic I came up with and it works very well: (click picture for full screen view)

(STRIPBOARD LAYOUT FURTHER DOWN THE ARTICLE!)

I based this schematic on the datasheet schematic for the LM317 and LM337. It calls for a 5K trimpot but I used 10K's because that's what I had and it works fine. Afterall you can trim it down to below 5K just as easy, so no problem there. The values of the electrolytic caps I'm using is way over the top compared to the datasheet but it does help stabilize the voltage especially because some modules, like Sample and Holds or Sequencers can pull a pulsed current from the powersupply. Here's a screenshot of the original schematic from the Texas Instruments datasheet:

The transformer you use for this power supply must be about 2 to 3 Volt higher in output voltage than the needed output voltage of the powersupply. There is going to be some voltage drop over the voltage regulators and the diode rectifiers that must be accounted for. However the voltage will also be higher than the transformer delivers when it comes out the diodes so we must also account for that. I find 2 x 17Vac secondary outputs to be about the sweet spot. You can go a bit higher if you like.

In the schematic above you can see that the output capacitors are 1000µF. They don't have to be this big. 100µF will do nicely too. The caps discharge through the 220 Ohm and 10K potmeter when you switch off.
If you need a power supply that can handle more current, say 10 Ampères for instance, then you can easily adjust this circuit by adding a 2N3055 on the positive side and an MJ2955 on the negative side. You can even put more power transistors in parallel over eachother to get even bigger current specs. Move the capacitors that come after the LM3XX's past the transistors but put an extra 100nF capacitor between the base and the null to suppress transients etc. Use Google to find more specific schematics for that, if you need it.

But for a modular synthesizer those alterations are not needed because the individual modules I'm going to build won't draw much current at all. It's mostly in de 20 to 80 milli amps at most. The only transformer that I had that was big enough for this project didn't have a center tap but it had two independent secundary outputs. One at 21V and one at 17V. This was close enough. I connected one wire from each output together to make a center tap and made a circuit board to build the powersupply on. (Make sure when you connect two secundary windings together like this, that you measure the AC output before proceeding with the next steps. If you connect the wrong wires the 2 voltages will try to cancel eachother out. It won't damage the transformer but you won't get any voltage out.) I didn't have etching fluid anymore so I cut different islands on the copperside of the copperclad circuit board I was using, with a dremmel tool with a milling bit. I had an old 25 Amp. Graetz diode bridge in my collection of components and after I drilled all the holes the build was pretty straight forward.
I used little trimmer potentiometers to set the voltage with. Once you set it, you don't have to touch it again but if you want to make it continuously adjustable you can of course use 10K panel mounted potentiometers with a knob. I put some LED's on the output side to indicate that all is working well. The difference in brightness will indicate if the voltages are set differently from eachother. You could also go the luxurious route and use two panel voltmeters to indicate the voltage but as I intend this to power my synthesizer that will not be necessary.
But if you build this as a stand-alone power supply, it would be a good idea to use two meters on the outputs. Beware with cheap Chinese digital voltmeters. They look great but they put a ton of noise on the voltage rails!! Use analog meters instead if you can. They look even better and are noise free.
The power supply as described above outputs between 1,5 and 25 Volts (dependent on the transformer you use) at a maximum current of 1,5 Ampere. If you want a more powerful version you could use the LM3XX regulators to drive a 2N3055 and a MJ2955 NPN and PNP power transistors as mentioned above and then you can draw up to 10 to 15 Amps. Be aware that the pinouts for the LM regulators differ from eachother. The correct pin numbers are noted on the schematic above.
The ripple is very low on the output. It's actually better than some you buy ready made. Make sure the electrolytic capacitors you use are rated 50 volts or higher. (I used 35V ones and that seems to work fine too but don't go any lower!) and make sure they are oriented the right way. Plus on + on the positive side and plus to ground and minus to negative voltage on the negative side. The voltage at the secundary directly after rectification can go up to 10 volt higher than the AC voltage from the transformer. Don't present more than 35V to the input pin of the regulators and be sure to use big heatsinks on both of them.
I've measured the ripple and noise of the power supply using the method outlined by Dave Jones from the EEVblog on YouTube in his video EEVblog #594 - How To Measure Power Supply Ripple & Noise
I used my simple home build 'brute force power load' described in the article from januari 2017 and under a load of 1 Ampere the Ripple Voltage Vrms was 6mV and Vpeak-to-peak was 10mV. Those are very good results.

Here's the stripboard layout for the powersupply. There are minor differences in values and components because this layout is based on an eBay kit, instead of the above datasheet schematic but it works perfectly, I assure you. You can mount the voltage regulators on a single big heatsink but they must be electrically insulated from the heatsink and eachother.

[NB: 11-Sept-2021 I just built one of these again today using this layout and it worked rightaway.]

You can leave the 10µF electrolytic capacitors over the trimpotmeters out. You don't need to include them. I put them in as an added protection for the LM3** voltage regulators but they are not needed. They are also not included in the schematic above.   

I included an L-Bracket symbol to show which part of the stripboard can be used for mounting behind a panel or in a case. The components are quite spread out so you can put them closer together to make the board smaller, I leave that up to you.

Here are some pictures of the first powersupply . As you can see there's some room left on the circuitboard for extra voltage regulators to get other voltages from the same supply:

I added the inductor coil in series with the Ground or Zero Volt pole to suppress any high frequency noise. It's just something I added as a test but you can leave that out.

It's a week later and I finished the power supply as I need it for my synthesizer project. It now has -15/0/+15V,  -12/0/+12V and -5/0/+5Volt. I looks a bit of a mess as my projects usually do but it works just fine. Here's a picture of the finished psu:

[EDIT: This is future Eddy speaking 5 years later. Having built over 60 synthesizer projects which have all been connected to this powersupply I can say it's a solid design. Many a time I have tested a module and had a short circuit somewhere but the powersupply always survived it.]

Obviously you can't plug in all modules in the same holes so I've build a power bus system to which I can connect every module I build. It's a bit crude and I use a lot of hot-glue to stick it all in place but it works just fine and it will all be invisible once the case is ready.

Below you see the connector I build. The pins carry the following voltages: From top to bottom in the pic below, the top 2 pins are ground or 0V. Then I took out two pins and stuffed the holes in the female connector with hot glue. This is to get an a-symmetrical distribution so you can't put the connector in the wrong way around. Then there's -15, -12 and -5 Volt and then we get +5, +12 and +15 Volt. I kept the plus and minus pins as far away from eachother as possible for safety reasons.

PART TWO. SECOND POWERSUPPLY for stage two of my synthesizer.
So, as I'm writing this we're 6 months on in the synthesizer build and I'm about to add a second stage to go on top of the synthesizer I have already built.
So I need a second power supply. The first design as seen above works so well that I'm repeating it for the second stage with a few minor changes. I'm using multiturn potmeters for the LM317 and 337 voltage regulators so I can set them very accurately. In fact, the one I just built has plus and minus 15.00V that's accurate to 1/100th volt. I'm using all LM3xx regulators for this because I have a lot of them and because their voltage doesn't drop if you pull more current from them which is important because otherwise the VCO's would become out of tune. I'm using the same schematic as above and I made separate stripboards for every stage of the supply. Here's the stripboard layout:

Bridge rectifier board. (Don't forget to cut the copper strip underneath the fuses and to tin all the copper strips that carry current.). You can hang more than one voltage regulator print off of the bridge rectifying board as long as the transformer and rectifying diodes can handle the maximum current of the combined regulator boards.

Voltage regulator board. (Again, make sure to tin all the copper strips that carry current). 

(Last revised: 30-Jan.-2021: Corrected connection of negative voltage indicator LED.)

SOME NOTES ON THE DIFFERENT COMPONENTS TO USE:
Don't get confused by Capacitors being of a different value on the stripboard than on the schematic. The electrolytic caps on the Rectifier board are the big ones. They can be 1000µF to 2200µF or even higher and they do the main ripple suppresion. On the regulator board the electrolytic caps can be smaller, like 100µF because the main ripple suppresion has already been done and these are there to suppress noise and such. 100µF is enough for that.
Diodes also. The diodes around the voltage regulators are simply safety valves. Their purpose is to prevent the output having a higher voltage than the input, which could damage the regulator. The circuit will work fine even if you leave the diodes out. You can use any type of diode you wish 1N4148, 1N4001 upto 1N4007. It doesn't really matter. The diodes on the bridge rectifier however must be types that can handle at least 100V and 1,5 Ampères. You can not compromise on those but there are many different types you can choose from so I didn't specify which type number of diodes to use. You can also use a Graetz Bridge Rectifier, that's 4 big diodes in one case. I saw a 1000V/4Amp one for 50 cents on eBay. Those will work fine and they won't even get warm.
Like I mentioned before, the voltage regulators must be mounted to a heatsink. Either use two separate heatsinks (make sure they can't touch eachother) or use one big one for both regulators but in that case you MUST insulate the regulators electrically from the heatsink otherwise you'll get a very short lived microwave oven with integrated laser lights. ^____^
Naturally the voltage regulators do not have to be mounted on the stripboard itself. You can mount them on the backside of a front panel, using that as a heatsink, or on the side of a metal case you're using and then you can wire them up to the stripboard with normal electrical wire. Use your imagination but do make sure the regulators are not electrically in contact with eachother, otherwise, boom!
The LED's are simply there as a visual indicator that the circuit is under power and they are not critical to the working of the circuit, so you can do without them if you wish. Use 15K current limiting resistors with the LEDs though, because lower values can get hot.

Should you have problems like not getting the right voltages out of the powersupply then check your resistor values. Are you sure the 220 Ohm is not a 220K? This has happened on at least two occasions I know of that's why I'm writing it here as a reminder.

Here are some pictures of the finished power supply. Tinning all the copper strips that carry current is important because they get very thin around the holes in the stripboard. 
I've mounted the whole powersupply on a long piece of MDF ready to accommodate the power-bus system I need to build.

I found some very old vintage diodes with a metal case which I think look very cool and they work fine. They are sturdy too because I had some short circuits in testing and the fuse went 2 times but the diodes didn't mind and I use slow fuses too so they did get some current through them.
Use plenty of heat sink compound on the LM's. The electrolithic caps are 1000µF each; all four of them and that's all the capacitance I put in. 1000µF in the rectifier and 1000µF on the output side of the voltage regulators. The rectifier caps have 10K 1Watt resistors over them to make sure the are drained of voltage when the powersupply is switched off. (It's 2K2 in the picture but they were getting slightly warm so I changed them for 10K's)

SIMPLE FIXED VOLTAGE POWERSUPPLY  using the 7812 and 7912 voltage regulators.

Finally I want to close off this article with a very simple powersupply that uses fixed voltage regulators. The 7812 for positive voltage and the 7912 for negative voltage. These can do up to 1,5 Ampères but I wouldn't use it for more than 1 Amp. otherwise they get very hot even with heatsink.

Btw, you must use these on a heatsink too, just like the previous designs, and you must make sure they don't electrically touch the heatsink if you have both regulators on one heatsink. Otherwise you get a short circuit and a lot of magic smoke. The circuit schematics for this one can be found by clicking here

Here is the layout I made for this PSU. It's very small and can fit anywhere. The LEDs are there to indicate if power is present on the outputs. You can mount those in a panel if you make a panel for your powersupply. I always mount leds like this near the ON/OFF switch for the PSU (Power Supply Unit).

(Last revised: 24-Aug-2022: Corrected a mistake where the LEDs were not connected to ground properly, thanks to a observant reader. )

Okay that's it for this one. If you have any questions you can leave them in the comments or post them on our special Facebook Group for this website, where we have a cool little community who will love to help you out.

If you find these projects helpful and you would like to support the website and its upkeep then you can buy me a Coffee. There's a button for that underneath the menu if you're on a PC or Mac. Or you can use this PayPal.Me link to donate directly. All donations go towards the upkeep of the website and components for new projects. Thank you very much!

ELECTRO-MAGNETIC FIELD DETECTOR.

Here is an easy to build EM Field detector with 4 stage LED strength indication and which has a wide range of applications. This circuit will detect electromagnetic fields and also static electricity. It detects the mains hum on a 240 Volt (or 110V) wall socket or cable without having to touch the object. It is enormously sensitive to any changes of the EM field surrounding it so it could be used to detect lightning (proof is in the video below) or maybe even ghosts. (No video proof of that alas! At least not yet  ^__^ ). Please note: this circuit can not be used as a metal detector.

Here is the circuit (click on image to display full screen):

(Last revised: 02-june-2020: Changed 1M potmeter for 20 to 50K potmeter.)

Parts list:

Transistors:
8 x BC547 

Resistors:
1 x 680 Ohm 
4 x 470 Ohm
1 x 220 Ohm 
1 x 4K7 
1 x 3K3 
2 x 2K2 
1 x 100K
1 x 1M 

Potmeter:
1 x 20K or 50K potmeter (use either a trimpotmeter or a panel potmeter if you're building this into a case.) 

LEDs (3mm):
3 x green, 1 x yellow, 1 x red

Diode:
1 x 1N4148

Miscellaneous:
9V battery clip, 1 switch (SPDT Toggle Switch ON-ON), 1 Bullet conncector for antenna. (optional)

Before I go on with the rest of the explanation, here's a video showing this EMF Detector in action in a lightning storm. In the background audio you can hear the crackle of the lightning on an AM radio I had switched on, and you can see that the meter lights up as the radio crackles and lightning occurs. Sometimes it even detects the build up of the electric field in the air before lightning happens. I'm not influencing the meter in any way. I'm just holding it by the 9 volt battery underneath. Here it is:

I designed this because I always found it a shame that these "everything detectors" or 8 Million times amplifiers never had a strength indicator so you could actually see if and how it's working. So I tried combining two pre-existing circuits and see if I could make them work together and it turned out to work very well. The first of these circuits is this 4 LED signal strength indicator

and the second is this circuit which is the actual detector stage, consisting of the 8 million times amplifier.

You can easily build this on a piece of stripboard.
The circuit needs only 8 transistors (BC547 or 2N3904), 5 LEDs and 11 resistors. The extra (5th) LED is there simply to function as a on/off indicator and could be left out if you so wish. I used 3mm LEDs on this project but 5mm will work too. Don't use LEDs that draw a lot of current though like bright white LEDs or blue LEDs. The circuit is fed from a normal 9 Volt battery.

The sensitivity of the circuit can be changed with the 20K or 50K potmeter. If you're using it like me, without a case, you can use a trim-potmeter. If you're building this into a little case then use a panel potmeter for sensitivity. Make sure there's a grounding point when you build it into a case. Some connector from where you can ground it.

The circuit is very sensitive and it reacts to all sorts of things. If you hold this EMF Detector  near any mains cables it will instantly detect the voltage, I noticed that if you hold it near metal it will detect that too and even in an open space it will sometimes indicate a field even if there's nothing visible there but it's not a malfunction because it will keep indicating on the same spot in the room. 

This meter works best if it is grounded properly, either by connecting minus to a metal case in which you build the meter and then holding it in your hand  or by  grounding it to some metal item (do NOT connect to ground of mains power supply!!!)
Here are some pictures of the detector I build:

Enjoy building this awesome little "everything detector" ^____^ oh and hey, while you're here, please leave a comment! That'll be cool! :-)

BAOFENG BF-F9V2+ Impressions.

This is just a little overview of my experience with the Baofeng BF-F9V2+ hand transmitter.

[Please keep in mind this review was written in 2018. I don't think this particular model is still available.]

I ordered mine from eBay and even though they're Chinese made transmitters, they all come from the United States. The are sold by Foscam or Baofengradios.us
Beware that since they come from the States, they come with US chargers that don't fit in European or UK wall sockets! (As I am situated in The Netherlands I just soldered on a European wall plug and covered the connections in hot glue and then with electrical tape. Works like a charm and it's safe too.)
I did a check on May the 12th 2019 and couldn't find a listing of these Hand Transmitters anywhere. It seems the BF-F9V2+ models are out of stock everywhere. It seems the new kid on the block is the Baofeng BF-UVS9+. This is the new model for 2019 but it doesn't seem to offer anything more than the older model except a higher capacity battery (3800 mAh instead of the 1800 mAh of the F9V2+), and a newly designed case which does look very cool and comes in 3 colours, black, silver and red.
It's also an 8 Watt model. They call it Tri-Band but they include in that the FM broadcast band on which you of course can not transmit. There are however also models that include the 200MHz range and are true tri-band hand transmitters.

Here's a picture of my BF-F9V2+:

Build Quality and Range:
This is a 3rd generation version of the well known UV-5R series of HT's and the exterior looks exactly like the UV-5RV2+ but it's most distinguishing feature is that it has the 8 Watt RF power option (although it doesn't really do 8 Watt, more on that later). I am familiar with FM transmitters and I know that in order to double your range with any transmitter, the general rule is that you need a 10 fold increase in output power. So I didn't think the extra power would have much influence on the range of this HT but it did have an effect. Not so much a big increase in range but an increase in penetrating power. The BF-F9V2+ has very good penetrating force. I must remark here that the first thing I did when I got this set is remove the original antenna and replace it with an original Nagoya NA-701. That is important because all the consequent testing is done with that antenna! Well, the signal goes through buildings and what have you like a hot knife through butter. For instance, I was underneath an overpass, a kilometer away from my house where the receiver stood (I used a UV 5RE+ with a Nagoya NA-701 antenna as receiver because at that time I didn't have a second BF-F9V2+ and I used a digital voice recorder to record the received signals.) I was inside my car with all windows closed and underneath that particular concrete overpass you're literally below ground level, and still the signal came in crystal clear. I was impressed I can tell you. That would not have worked had I used a normal UV 5R. An other thing I noticed is that the BF-F9V2+ has a better sound quality out of the build-in speaker than the UV-5RE plus. The BF has better low frequency sound. The UV sounds very tinny, with much more high frequency elements in the sound. The BF uses a new chip set with noise reduction features that block out noises caused by signal intensity changes and it also has a tail tone elimination feature.
The unit feels very solid. It's made from industrial plastic and has an aluminium frame inside. The loudspeaker is protected by a metal gauze over which they mounted a black anodized aluminium protection plate. This has a bevel in it which gives a shiny effect when the light hits it. It looks very cool. Also the lettering on the front around the LCD screen has a holographic effect which gives it all the colours of the rainbow if you hold it at different angles. On the back there is a spring loaded belt-clip which is made from plastic but feels very sturdy. It's the same one as on the UV-5R. I think you'd have to misuse it a lot in order to break it. The LCD display is protected by a hard plastic window so you can't touch the LCD screen itself whereas the UV-5R just has the display with the metal case around it. The UV-5R LCD-display is soft plastic and scratches easily in itself, but because of the raised metal edges it hardly ever scratches with normal use. The BF-F9V2+ has a hard plastic window over the display which protects the display but this plastic window is not protected by any metal so it will scratch in normal use. So that's a bit of a paradox. The protective hard plastic window should protect the display underneath from scratching (which it does) but because it is right at the surface of the unit it will scratch over time because things will rub against it. None of this is really important though in my opinion. They are meant to be used and hold up in daily use and they do. All the Baofeng units are very sturdy and excellent value for money.
One tiny thing on the front panel is different to the UV-5R; it's missing the 'Band' button. Leaving that out was a wise decision by the designers, because I don't think anyone ever uses that button. It's not needed because the band is selected automatically when you enter the frequency.
The unit comes in a nice brown box with a 74 page manual for which you'll need glasses with enormous magnifying power to be able to read it. The letters are 0.9 mm high. (Yes I actually measured them ^__^) It is however a very useful manual. It tells you everything you need to know, including how to program it. If you're sensible though, you should get a programming cable from eBay so you can use "Chirp" to program it. For those of you who don't know Chirp. It's free software you can download from the net and which makes programming this unit a breeze.
You can download CHIRP directly by clicking here.

The frequency range is as follows:

65 to 108 MHz (FM Broadcast band, receive only)

136-174 MHz (VHF) I found that it still works as low as 131 MHz and as high as 177 MHz.  You can transmit and receive from 131 to 177 MHz without problems. You can type in 130 MHz on the BF-F9V2+ and it will transmit but it only transmits weird beeping sounds. You can see it's not designed to transmit on frequencies as low as that, but the software does allow you to type it in. If you type in frequencies between 178 and 179 MHz and press the PTT button it just goes on transmitting even if you let go of the PTT button. You need to switch the unit off in order to stop transmission. It works fine up to 177 MHz though.

400-519.990 MHz (UHF) The UHF range is listed as 400 to 480 but goes up to 519.990 without problems. However, I tested the signal on my oscilloscope and it looks more like a modulated AM signal than an FM signal so I wouldn't use these frequencies if I were you. You can type in 520.000 MHz but again the transmission will go on even if you let go of the PTT button and you need to switch off to stop it. It's not designed to go that high. Best keep within the advertised ranges at all the bands.

The 5 bar signal indicator does actually work. It doesn't just go on or off if you receive a signal. It actually shows more bars as the signal gets stronger. This does not work if you press the Monitor Button. Then you just get all 5 bars at once. So there's a working signal strength indicator on all Baofeng HT's  (not just this model) but it's so small you can hardly read it. Oh well. =)

FUN FACT:

Did you know that the ON/OFF and Volume knob can actually be used as a tool to tighten or remove the fastening ring on the antenna connector? If you pull the knob off the radio you'll see 4 little stubs in there that fit inside 4 little notches in the screw ring that fastens the antenna connector. So you can use it to remove or fasten that ring should it come loose.

RF Power:
I measured the output power on a Diamond SX-600 SWR/Power meter with a 50 Ohm Dummy-Load attached as antenna and I measured an output power of 6 Watts on the 2 meter band (VHF) and 4 Watts on the 70cm band (UHF). That is less than advertised but it is still 2 Watts more compared to the UV-5R on both bands which I measured at 4 Watt and 2 Watt respectively.

The BF-F9V2+ with 2 UV-5RE+'s behind it. Note the lettering which changes colour according to the angle at which you hold it. It's the same in outward appearance as the UV-5RV2+.

BF-F9V2+ with the Nagoya NA-701 antenna. This is the antenna that I find the most useful for these HT's. Although the Nagoya NA-771 is a bit better it is also 38 Centimeters long (15 Inches). The NA-701 is 20 cm (8 Inches) long, which is much more practical. The original Ducky antenna is just 14,5 cm (5.7 Inches) and is pretty much useless. Get rid of it as fast as possible.

The inside is Aluminium and the battery is in a sturdy industrial-plastic casing.

Here is the complete manual in PDF form: click here

EDIT: In the recently started conflict between Russia and the Ukraine, I saw a Ukrainian soldier on a news item with a Baofeng UV5-R. It seems they are ideal for communication in close quarter fighting because of their long range, clear sound and long battery life.

That's is it for now, thank you for reading this. I hope you found it useful and if you did, I would love for you to leave a comment. Let me know your thoughts on the Baofeng products!
See you later!

LED Oscilloscope with 100 LEDs.

Hello everyone,

One word before we start: Don't build this project if you're in need of an oscilloscope for measurements or checking waveforms. This scope has no trigger and therefor no stable waveform unless you exactly match the frequency of the waveform with that of the timebase. Furthermore, 10 by 10 LEDs is way too low a resolution to check waveforms with. If you need an oscilloscope for audio waves you can start with a cheap one from eBay for $20. (Buy one with acrylic case!)
This project is just a fun thing to build with LEDs, Something that actually visualizes audio in a small way. And that's all it is; just a bit of fun.

Okay, with that said, here we go:

Following on from my 81 LED chaser with 2 NE555s I now set out to build a LED oscilloscope using the same type of LED matrix I used in the last project, only this one has 100 LEDs instead of 81.  First of all I'll show you the circuit schematics I used for this project. You can easily find this on Google and it's a very simple design. Actually easier to build than the 81 LED chaser.

I made some changes to the way the NE555 was configured. To test the schematics I build this pulse generator on a breadboard and took some measurements with my oscilloscope and the pulses that came off only had a duty cycle of 6%. Maybe that was meant to be and actually works better, but I changed it to a design that gave a 50% duty cycle. I wanted to be able to extend the range of frequencies by adding the possibility of switching between capacitors on the 555 and I wasn't sure how this short duty cycle worked on the higher frequencies I intended to put in, and I also didn't have a 500K potmeter. I only had a 100K so I needed a design that gave me a good frequency range with a 100K potmeter. Here's what I came up with:

When set to the highest capacitor value (330 nF) this gives a range of 17,5 Hz to 6,2 kHz. Then, by choosing the lowest value capacitor, it goes up to about 650 kHz. That's a nice range for a timeline I thought. The ranges overlap a lot and you only really need the first and last setting but I liked having some choise and it adds yet an other switch to the front panel which always looks cool :)
After I had build this circuit I came to the conclusion that the higher frequencies for the timeline don't look good at all because this scope doesn't have a trigger-mode. So with high speed signals it just looks asif the LEDs are on all the time. So you don't have to bother with the alteration to the NE555 and just keep to the original schematic. I just thought I'd include it in this article in case you had the same idea ;)
Do not forget to put in the 470µF electrolytic capacitor (even if the circuit is fed from a 9 volt battery). This prevents oscillations on the positive voltage rail caused by the NE555. (I had the same problem with the 81 LED chaser. This is a well known issue with the normal NE555 chips but if you use a LM7555 cmos version of the 555, this problem won't occur). The capacitor makes sure you get a nice ripple free supply voltage, which needs to be 9 Volts btw. I also put a Schottky diode in the positive voltage rail to prevent damage from accidental polarity reversals. This circuit draws between 24 and 34 milli-amperes (depending on the frequency of the timeline) so it can easily be fed from a 9 volt battery.

I proceeded to build the LED matrix first and I wanted to make a better job of it than I had done with the LED chaser. So I again had to grind down 100 LEDs on 4 sides to make them fit tight together on the perforated circuitboard. I had to glue on an extra bit of circuitboard because I could only fit 9 rows of LEDs on there and I needed room for ten rows. After I had soldered them all in place I took my Dremel tool and shortened all the negative leads so I could fit the positive rails over the negative rails without them touching and creating a short circuit. Here's a picture of the backside of the LED matrix which came out very well. (You can see the extra strip of circuitboard I glued on at the left side):

After that I proceeded to solder together the rest of the electronics which was quite straight forward really. I did end up with a mess of wires and knobs etc. but that was unavoidable. But it was going to be build into a nice case anyway. Here's the finished product mounted in its case but still very accessible because only the display is glued into place so changes and repairs can easily be made.

Here's a closer look at the switch with the different capacitors on it, to change the frequency range:

And here it is in full working order:

Problem solving:
I did encounter a little problem after I had assembled the scope in its case. I had made a BNC connector on the front panel to attach a probe to but it turned out that the ground wire caused the 3rd column of LEDs to turn off so I cut the ground wire for now. I need to mount the BNC connector in such a way that it is insulated from the case completely.
I also build in the microphone with the little amplifier which you can see in the schematic on the lower right. This works very well and I put in a switch to choose between the microphone or the probe. But I wanted an amplifier that is a bit more powerful and has a volume control button that I can put on the front panel aswel. In the next paragraph I explain how I did that.

The Amplifier:
Like I mentioned above, I wanted to build a more powerful microphone amp with a volume control to put in this scope. Well, recently I did just that. It took me just over an hour to build it and put it in and it works very well. The mike is much more sensitive now and reacts even to random noise it picks up. I build it with a 2N3904 transistor as a pre-amp for the electret microphone and then a LM 386 to amplify the signal. Here's a little sketch of the circuit:

(Last revised: 08-Feb-2020 Changed 10µF cap on pin7 for 100nF.)

Here's a picture of the scope with the new volume control added to the front panel:

Here's a little video of the scope working (with a bit low battery) with the synthesizer I build. There are no knobs on the scope this time because I needed them all for the synthesizer, LOL :)  :

I can really recommend using this design over the microphone amp in the main circuit schematic. This one works much better.

Okay, that's it for this project. I hope you enjoyed this read and if you did please consider supporting me by subscribing to my YouTube channel EdEditz or by following this blog or clicking on the adds.

If anyone has any idea how to incorporate a trigger section into this scope I would love to hear from you!!
If you have any questions or remarks, feel free to post them beneath in the comments or on my YouTube channel. I always love to hear from you!!!