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! :-)

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!!!

81 LED Chaser circuit using 2 NE555's!

Hi everyone!

This last week I've been busy making a little LED chaser circuit. I found a schematic online that used one NE555 to drive two CD4017 decade counter chips that drive the LED's. I thought I could improve on that by adding a second NE555 and it worked beautifully.

BTW, AliExpress now sell a kit of this design, only it has 9 x 9 LEDS, for about $5,-

I started out by building the LED display on a separate perforated circuitboard. I wanted to have the LEDs very close together to get a nice dense row of lights and the board I used was exactly the right size to fit a 9 by 9 LED matrix. I used 5mm LEDs because I have about a thousand of those in my junk box, salvaged from an old display unit. They had short leads but long enough to still use. I used a green perforated circuit board but to fit them on next to eachother I had to trim each LED on 4 sides with a Dremel tool because these LEDs have a broad rim at the bottom. Anyway, I managed to fit them all on the board in a 9x9 matrix. Then I soldered all the Cathodes together, row by row. Then the same for the Anodes, to give me an X and Y axis to work with.

You can use other types of LEDs if you want and choose a resistor value for the collectors of the transistors that works best with your preferred LEDs. Test the LED/Resistor combination on a breadboard and choose a value that makes the LED shine at normal brightness.

After that I started soldering the actual circuit.
Now, the original schematic, that you can find on the internet, only uses one NE555 to drive the movement of the LED lights and so you can really only change the speed of the X-axis of the display, or the Y-axis according to the schematic below, but I soldered the display in such a way that the initial movement was horizontal. So I thought why not add an extra NE555 and make the Y-axis adjustable aswell so you can get much more variation in the patterns displayed. So that's what I did. I made a new schematic and here it is: (Btw, the collectors of the vertical row of transisitors are all connected to the + of the power rail, just like the top transistor. It's not shown in the schematic because that would make the drawing very messy.)
(Click on the images to see them in full scale and right click to download them.)

Btw, instead of using the BC547 transistors you could also use the 2N3904 but in that case you need to change the 220 Ohm resistors for 100 Ohm resistors, but my advise would be to test the LED/resistor combination on a breadboard and see which resistor value works best and makes the LED shine at a normal brightness. You could also try 2N2222 transistors). The 10K's at the Base of the transistors should always be the same to protect the Base input.

OSCILLATION PROBLEMS (solved ^__^):

After having soldered on the first NE555 squarewave generator, I tested the output signal with my oscilloscope and I found that there were bursts of pulses with a frequency of about 60kHz on the output squarewave. This is a common problem of the NE555 which does not occur with the CMOS version ICM7555.
Here's a screenshot of the Squarewave from the NE555 with the pulses on top:

I added a big electrolytic capacitor of 470 µF to the output of the voltage regulator and that solved the problem. I proceeded to solder in the rest of the components. The 10K resistors for the base of the transistors I stuck into the same hole as the base, to save space. I had a bunch of cheap resistors from China which had very thin leads so they just fitted into the hole together with the base of the BC547s. That way I only needed 4 holes per transistor resistor combination.
I tested the circuit a few times during assembly to make sure everything worked because once it was all put together it would be very difficult to trouble shoot this thing with all the wires going everywhere. Luckily it all worked as I had imagined, especially the second NE555. It worked just as I thought it would do. I had a problem though with the two 100K potmeters. The ones I used were old ones from a valve radio and they turned out not to be up to the job. I didn't have more 100K pots but luckily I did have two 50K stereo potmeters, so I soldered the wires on, in such a way that the double 50K was in series and formed one 100K potentiometer and that worked very well. It's important that the potmeter goes all the way down to zero Ohm to get the fast movement of the LEDs and the ones I used did that very well.
Btw, if you decide to build this and want the display to appear as I have it in my video, with the lights going from left to right working their way down, you'll need to experiment with how you solder the wires from the transistors to the display. The way it's drawn in the schematic the light would go from top to bottom instead of left to right down the rows. Beware of that.

I made a video about this circuit which shows how it works with a little animation sequence, which you can watch here:

TESTING:

I did some measurements of the pulses and they are pretty messy to look at but they work just fine to trigger the CD4017s. I was surprised at the fast rise-time of the output pulses from the 4017s. They rise in about 12 nano seconds! Here are some screenshots from the scope:

This is the X-axis pulse going to the LEDs:

This is the Y-axis pulse going to the LEDs:

Here's a closeup of the rising edge of the output pulses showing how fast they rise. You could build a Time Domain Reflectometer with pulses this fast:

So now that I had it all working, I decided to round off this project by building the whole thing into a nice case. I found an old sewing tin which had just the right size. I spray painted it black and with a Dremel tool I made holes for the display and the knobs. Then using hot glue I glued in the display board. I left the board with the actual electronics on it floating. I didn't glue it down. All the wires connecting it to the display were enough to keep it in place and I needed the lid to be removable to make it possible to exchange the battery. I used a 9 volt battery which I kept in place with a strip of copper, bent to fit around the battery and glued to the bottom of the case. I lined the inside of the case with gaffer tape to prevent accidental short circuits should the print touch the case. I had just received a batch of knobs from China that looked a lot like the knobs on a Mini-Moog synthesizer and I put those on the potmeters.
After it was all assembled it looked like this:

This is the inside of the case:

(The hot glue underneath was meant to protect the wiring when I was testing the circuit.)

Doesn't it look cool?? Of course it doesn't do anything useful, but it's so much fun to play around with and also to build. Actually, you could use it as a game: try and make a diagonal line appear that doesn't move across the screen. It's possible but requires a very delicate touch on the controls. Perfect to while away those busy office hours, lol! And you could use it as a prop for a movie. Say like an artificial scanner of some sort, for tracking down ghosts  ^___^

Okay that concludes this blog post. I hope you enjoyed it and if you did please leave a comment, either here on on the YouTube video. If you want to support my channel you can do so by subscribing. That would really help me out and it costs you nothing :) Win/win situation!  :) But please leave a comment. I always love to hear from you!!
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https://www.patreon.com/EdEditz