DIY Oscilloscope

P

P. Short

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Being away from home and thus away from most of my equipment and parts, I'm returning to partially finished project from the past. It's a 3-channel, 2Msps DIY oscilloscope. It uses a Wemos Mini to send data to a PC for display, a dsPIC33FJ06GS101A as the ADC, and an op-amp front-end to level-shift and scale +5V to -5V analog signals for input to the dsPIC component. The board is approximately 1" x 2.1", and I will probably never put it in an enclosure.

This project is mostly meant for myself when travelling, so for simple, low-speed designs I don't need to pack the larger COTS digital oscilloscopes, as several of my plane trips have been with just a back-pack without checking luggage or taking a roll-on. When I first revived this project on this trip I intended for the output to go straight from the PIC to one of those 8-ch/24MHz el-cheapo logic analyzers, but realized that I would have a lot better control of the display by using the Wemos to send data to a laptop (which I would always have along on trips).
 
Ever looked at Saleae? Sure not super cheap, but works great. I bought my first one when they were on kickstarter (?) or at least when it first arrived on the scene. Software is what makes or breaks tools like this. I've been impressed by what they have. Having said that, part of what we enjoy is building something ourselves to solve a problem, so by all means I applaud you for the work you are doing!
 
Utimgr said:
Ever looked at Saleae? Sure not super cheap, but works great. I bought my first one when they were on kickstarter (?) or at least when it first arrived on the scene. Software is what makes or breaks tools like this. I've been impressed by what they have. Having said that, part of what we enjoy is building something ourselves to solve a problem, so by all means I applaud you for the work you are doing!
Click to expand...

Do you have a link? They appear to be more in world of logic analyzers than oscilloscopes, unless their logic analyzers also have analog capabilities.
 
yes they are both a logic analyzer and a scope! The original version was just logic, but they added analog capability a few years back. So you can have a digital trigger and 7 analog channels...mix and match as you like. Or 16 channels mix and match.

https://www.saleae.com/
 
Utimgr said:
yes they are both a logic analyzer and a scope! The original version was just logic, but they added analog capability a few years back. So you can have a digital trigger and 7 analog channels...mix and match as you like. Or 16 channels mix and match.

https://www.saleae.com/
Click to expand...

Got it. Even the lowest end of their line (Logic 8) is pretty expensive at $499, and the analog specs aren't so great. I'm happy with my current tool kit of the HiLetGo 24Msps/8ch logic analyzer + future 3-channel oscilloscope. In many respects it's not as good as the Salae, but the cost to me is ~50$ for the pair (or it would be if I only ordered the parts for one in one Mouser order).
 
Well keep us all posted on how it goes! Many of us design a tool or a "thing" because we want to learn, or just are not satisfied with commercial offerings. What you have created should be a low cost yet amazing tool. Thanks for sharing!
 
Dirk can tell you easily I'm distracted...the delays between ordering a pcb and receiving it leaves too much time for me to think of something else to do.
 
Only takes me about a week to get my blanks in....but i agree, that sometimes allows more projects to creep in :)
 
This is going to be more difficult than I thought - the hard part is the communications between the dsPIC and the Wemos. I may have to switch to using an ESP32 board, maybe the ESP32-CAM module. The alternative is fall back to targeting a 1Mbps sample rate instead of 2 Mbps.
 
I like the PicoScope as it has deep memory, there are many triggering options, the software is pretty good, etc. but it's like $3k for 4 channels and MSO. Is there anything like that at like 1/10 of the price? I don't need the 200MHz. I am fine with 1/10 of the frequency for 1/10 of the price...;)
 
I think I've figured out a way attain 2 Msps. The main difficulties up to now revolve around the different clock frequencies involved and the clocks being totally asynchronous wrt to each other, and the relatively slow i/o performance of the ESP8266. I've found a way around that involved adding two msi chips to the design, although this necessitated increasing the board size to approximately 1.25" x 2.5". There's a lot more work involved...
 
Those are interesting, but in a totally different league.

I've not spent a lot of time looking at those, but a few apparent differences:

What I'm working on is a lot cheaper.
It's totally isolated from the power line AND the PC, yet uses a PC for display and control.
It can be modified for 10 bit (via s/w but likely lower sample rate) or 12 bit (processor swap in the same socket, also lower sample rate).
Physically smaller.

I own standalone 'scopes with much better specs, this project is for traveling light.
 
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