M5Stack 2 Channel Oscilloscope

Calin

I fixed the speaker noise issue much much easyer.
Please check the updated version on: https://github.com/botofancalin/M5Stack-ESP32-Oscilloscope

BTW!!!
The project is compiled on Visual Studio using the awsome vMicro plugin : http://www.visualmicro.com/

daslolo

The DSO112A generates signal that's ok clean.
This M5Stack oscillo graphs something far noisier.
Why is that? Can this be fixed without lowering the sampling rate by smoothing the analog signal?

EDIT: I connected to the wrong wires and didn't ground. Once grounded, disconnected USB and pinned to 35, the signal is very clean. Weird that I'd get a squarish signal when connected to AD
alt text

Calin

The maximum voltage on ESP32 ADC can read is 3.3v
The ESP32 don't have the voltage divider on ADC in as the DSO oscilloscope have.
Noises can cause high voltage levels, especially near computers, where you have lots of radio waves on different frequency. So even touching the input pin (35) with your hand, the voltage at the input pin can cause more than 3.3v, especially if the ESP is connected to PC by USB cable.

Some basic filters and voltage dividers at the input pin, can solve that problem.

daslolo

@calin and the ESP32 can be damaged by spiked above 3.3V, I read. How do I know if I damaged mine?
I'll add voltage divider, is there a way to remove spikes without killing the sensitivity? I am doing an FFT on the signal and don't want to smooth things out too much.

Calin

If the DAC input was damaged, it won't pick up any signal that you feed to it...

Calin

Btw... check out the new development: http://forum.m5stack.com/topic/165/m5stack-multiapp-firmware

daslolo

If I understand this correctly, the ESP32 analog input captures only positive voltage.
How do I get the full -/+ range in there?

Calin

Make a voltage divider with 2 resistors (100k or so...) with one end connected to GND and the other end to 3.3v.
The middle of the divider connected to oscilloscope input pin.
Apply input signal to input pin and you get +/- 1.65v input range.
I designed the code to be used with this divider, that's why, without the divider, the oscilloscope line is at the bottom of the screen.
Once you connect the divider, the signal line will be at the middle of the screen just like on a normal oscilloscope.

daslolo

Without the voltage divider, the amplitude is the same, just offset by 1.65v?

Calin

The max amplitude is 3.3v. With the divider, the amplitude will be -1.65v to +1.65v (total 3.3v) The aplitude can be solved easy with a series of resistors at the imput. To change the input aplitude, replace the 10K resistor on the example below:
0_1523452685767_Vontage divider.jpg

pkourany

@calin 在 M5Stack 2 Channel Oscilloscope 中说：

he amplitude will be -0.65v to +0.65v (total 3.3v)

@calin, I think you meant the input signal range will be -1.65v to +1.65v (total 3.3v). :)

Calin

@pkourany 在 M5Stack 2 Channel Oscilloscope 中说：

@calin 在 M5Stack 2 Channel Oscilloscope 中说：

he amplitude will be -0.65v to +0.65v (total 3.3v)

@calin, I think you meant the input signal range will be -1.65v to +1.65v (total 3.3v). :)

yes. sorry for typo... edited now :)

JJ

Awesome oscilloscope case - designed by Macsbug - infos here

daslolo

This post is deleted!

ChrisWR

Its restarting every 5 seconds making it useless.. what can be my problem?

ChrisWR

@chriswr Ok solved.. disable the watchdog..

disableCore0WDT();
disableCore1WDT();