The DSO-138 Oscilloscope Build
So I thought a few months ago that I would give the DSO-138 Oscilloscope kit (approx. £15) a go. I wanted to get some more hands on experience with PCB’s and soldering whilst studying my Electronics Engineering Masters.
The Build
The kit is pretty straightforward with everything marked up and decent instructions. I would certainly recommend, as many others do, testing each component individually prior to soldering.
A few good YouTube videos that are worth a look prior to and during the build are:
https://www.youtube.com/watch?v=OISEu-Bm8_s
https://www.youtube.com/watch?v=4Lsp5YZgsZU
As you might be able to see from the picture, my soldering is a little ropey but everything felt strong and the board works fine with no issues. I only had some cheap solder with me, which took a while to melt onto the board in places and certainly something I’ll avoid in future. All part of the learning process!
I would also make sure that the ring you solder in for the test signal rises up quite high. A problem I have now is that because I put in a small ring (a cut off from a resistor leg), it doesn’t match very well with the hole in the case for it (vaguely see from the below picture, second hole from left). This is not a big deal but worth mentioning if you are putting it into a case afterwards and may want to use the test signal.
Circuit Troubleshooting
After initial soldering and assembly, I tested the circuit and it didn’t work! I checked the voltages and they looked ok to start with but were -ve and very low in some places. This taught me about PSU polarity, a really basic concept in hindsight, but not one I had come across before on a practical level. I figured this out through the good old use of asking a forum!
My issue was that the PSU I was using was one I use with my guitar pedals, which are -ve polarity and I needed a +ve polarity PSU for the DSO-138 (I didn’t realise this at the time!). Fortunately for me, there was a protection diode in place (probably why my voltages were so low as I guess that was leaked voltage).
That was basic lesson 2) of troubleshooting........what protection diodes are and how they work. Again, simple, basic and key and this information will certainly help me in future if I decide to design my own circuits - and save me some components!
After changing the PSU to a +ve one, all was fine and the board worked with the correct voltages.
Acrylic Case
I bought a case for the scope off EBay (for about £5) to finish off the project. There are no instructions so I used this video to help:
https://www.youtube.com/watch?v=FlniY41j7B0
One thing to watch out for is the Power Inductor. On the version I bought, it is quite big and doesn’t allow the case to go together correctly. To right this, I filed a bit extra out of the case layer that obstructed it and it then fitted fine.
The case available (I don’t think they are strictly official?!) is strange as its kind of like a perspex puzzle but it does the job and saves leaving an exposed circuit board as a finished project.
Firmware
In terms of the Firmware, it does come with working firmware but to update to the latest version I bought a cheap USB to TTL adapter for about £2 (again from EBay). It was a bit of a fudge to do but I used this video to help guide me through:
https://www.youtube.com/watch?v=fDtqO2wDdHk
Project Review & Final Thoughts
I really enjoyed this project. It was the first I had done like this and learnt a huge amount in the process whilst feeling I achieved building something that worked. I was glad that it worked after very little troubleshooting which is great to keep the momentum going for future projects and added verification that my careful, slow approach and testing everything paid off!
I’d certainly recommend the kit for people in my position wanting a bit of hands on experience whilst actually building something useful. I think the range of the oscilloscope is up to 200kHz so it’s not hugely useful on a practical level (nor is it likely to be extremely precise), but it is a cool demo toy and might come in handy for experimentation purposes in the future!
In total (not inc things like solder), the project cost was approximately £28 (£15 for the kit, £5 for the case, £8 for the PSU).
I realise now (after purchase) that the particular kit I bought, is actually a knock-off from the original. The original is made by JYE Tech (http://www.jyetech.com/Products/LcdScope/e138.php) so please buy from there if you are interested in the kit as they are the original designers!
