Sunday, 26 January 2020

Synthesizer Build part-19: CHEAP OSCILLOSCOPE for the synthesizer.

A cheap but good functioning little oscilloscope that you can buy on eBay and use for your synth.

As a vital addition to my synthesizer I bought this little oscilloscope so I can easily check the signals my synth produces, so I can keep an eye on things and easily check if something is broken. I couldn't include it by giving it its own panel because I had no more room for that in the synthesizer so I decided to make a special holder from aluminium that goes over the case and holds the scope and has a mono 3,5mm input jack to which I can connect a cable from any output I choose.

The scope I bought is the little DSO138 that you can find on eBay or AliExpress or many other sites for around $20 dollars. If you order it, make sure you get it with an acrylic case because the buttons are on a lower PCB than the screen so it's not easy to make your own case for it. You can order acrylic cases for this scope for about $5 dollar.

If you are new to DIY synthesizer building I strongly advise to get one of these!! You are going to need a scope for trouble shooting so get one! If you can, buy a good multi channel digital oscilloscope, a really good one, like the Rigol DS1054Z 4 channel oscilloscope that I use, or a Siglent for instance. But if you can not afford to invest that much, just get this cheap scope. It'll do for 90% of the testing you're going to have to do. For tuning filters and testing VCO's you can't do without one.

Here are some pictures of how I use the scope:

As you can see I used a Banana plug to BNC adapter on the input and then some thick copper wires to the 3,5mm mono jack input. The holder is made from 1.5mm thick aluminium which I had left over and I decorated it with that circle pattern using a Dremel tool because it was scratched. Looks really cool I think. This is an ideal set-up because I can move the scope over almost the full length of the synth so it's never in the way. All the buttons are within easy reach and it is powered from the power supply from the synthesizer itself. There's a little wire coming out of the back of the synth that plugs straight into the scope.
[Edit: Room to move it around? Ha, the next article will take care of that. No more room for anything after that, LOL]

The oscilloscope menu is not very clear and user friendly. The documentation doesn't explain it in depth at all so here is a little explanation of the scope-menu:

Use the  [SEL] (select) button to go between the different options. There's no need to confirm settings with the OK button.
The option you selected will have a square around them, at the bottom of the screen, but there are a few options that are hidden from normal view. I'll explain those here:
With the 'trigger slope' selected, press [SEL] one more time to change the trigger level. You can see it rise or fall by the little arrow on the right side of the screen. (Use + or - to move it up or down.)
With the 'trigger slope' selected, press [SEL] two more times to change the zero level. This changes the position of the waveform on the screen up or down. (Use + or - to move it up or down.)
To display all the parameters like frequency, voltages, duty cycle, etc. long press the [OK] button (the top button) and the text display will turn on. At the same time the 'Hold' function will engage so you'll have to short press the 'OK' button again to get the scope running again. Long press again to turn the text display off and then short press 'OK' again to turn the waveform display on again.

The scope is delivered with lots of documentation to show you the different modes for triggering and what all the switches are for so I'm not going to go into that here. If you have any questions about this scope you can always put them in the comments below and I will answer them for you as far as I can.

If you are really serious about your DIY synthesizer hobby then I strongly advise to fork out some cash for a digital oscilloscope. I myself use a Rigol DS1054Z 4 channel oscilloscope which cost me €400,-- but you can get a reasonably good 2 channel one for under 200 US dollars these days. Here's a link to a Hantek scope that'll do the job nicely and will serve you well for a long time.

So that's how you can add a little scope to your modular setup for a minimum amount of dosh. I hope this was of use to you and you enjoyed this article. Please leave me a comment below and I'll see you on the next one.

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