PI Pico Oscilloscope

[simba15]

So I recently saw this very nice Android Oscilloscope for use with the Pi Pico.

I plan to test if it can work in Bluestacks or other android emulator for PC and Linux.

The app is simple yet user friendly. I was actually impressed.

https://github.com/fhdm-dev/scoppy



The APP uses 2 channels for input and 1 channel as a function gen ( all from the Pi Pico hardware.)

This is all very low cost ,Full app is $1.89!! ( Practically free)  and the Pico is a whooping $4.00

The only issue with this scope is the lack of front end, as the pins are limited to 0 to 3.3v.

The developer has provided some designs and I hope to start a further discussion here about the best methods to get  a reasonable voltage range and input voltage protection.

https://oscilloscope.fhdm.xyz/wiki/front-end-design-4

Special thanks to the Devloper fhdm-dev ( on GIt)

[simba15]

So I have built a few of the front end designs for this scope.

So far all works quite well.

I would like to use a standard x10 probe with the device.



The input impedance would need to be 1m and the Capacitance would need to be 117pf.

Any simple changes that could be made?

[Kleinstein]

The input resistance is set by Rg1 + (Rf1  in parallel to the input impedance of the OP). So with a slightly different resistor ( ~ 330 K) one could get close to 1 M input resistance.
The input capacitance needed for the standard probes is in about the 15 to 30 pF range (some probles are a bit more tolerante to one side).
The usualy way is to also have small capacitors in parallel to the divider at the input, some maybe some 33 pF in parallel to Rg1 and some 15 pF in parallel to Rf1) . The ~15 pF would need to be trimmable to get a reasonable good response to a square wave (like the probe compensation).

The LM324 is a rather poor choice, as it is relatively noisy and also high bias. A more suiteable OP would be a low noise CMOS rail to rail type like MCP6272.
A sensible alternative may also be a programmable gain amplifier like MCP6S21.