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8:36 AM
So, I've got a problem here where my ESP32 can't sample a sensor voltage (1) fast enough, and (2) without massive noise effects
I want to sample at at least 330 Hz, with 12 bits of resolution. But my ESP32 can only seemingly get around 100 Hz poll rate with so much noise that I can't make out the signal at all
However the oscilloscope can when plugged into the sensor (amplifier) outputs
I've tried adding some small capacitors in parallel with the ADC pin as suggested by the vendor of the ESP32, but it made no difference.
 
JRE
@Micrified Have a look here. If that doesn't help, post a question on the main site. Include your full schematic and your code.
 
@JRE Yes I know of this document. I used it to configure my device to read from the ADC pin
My problem is mostly that it is too noisy
 
JRE
Scroll down to the bottom. There's a section on reducing noise.
 
9:35 AM
@JRE Yes, this is where I mentioned "I've tried adding some small capacitors in parallel with the ADC pin as suggested by the vendor of the ESP32"
I followed their advice but it did not help.
I'll try again today in the lab
But here's what was really frustrating
Input: Square wave to sensor, Oscilloscope: Slightly noisy with distinct peaks, ESP32: Huge block of noise with random peaks
Anyways I can make a post about it on EE and maybe someone will know
 
JRE
@Micrified Probably best. That sounds like more than just noise.
 
The ESP32 is running FreeRTOS, and the task I have can only sample around 100Hz max, whereas I would like sample around 330 Hz
IDK if this could be a reason. My guess would that this shouldn't cause noise, but just an under sampled single.
signal*
I'll try pinning the task to one of the ESP32 cores and see what I get
 
 
4 hours later…
1:31 PM
@JRE I fixed the noise problem it seems
Used a different pin for the ADC and it's much better. Still its with a function generator
The input is a 100mV square wave at 1Hz
to the sensor
 
JRE
1:47 PM
@Micrified Were you using ADC2 and getting conflicts with the WIFI?
 
@JRE No I disabled WiFi
And checked for errors
pertaining to that
Anyways now I tried the EKG sensor with actual probes on myself and it seems okay
 
JRE
"EKG" Thought those spikes looked familiar.
 
Yes but you know what is strange.
The module produces an "ekg" for a square wave input
Which makes me think it just fakes the form
When it finds a "spike"
 
JRE
What module?
 
Some Sparkfun hobby stuff, based on the AD8232 op-amp / filter
The IC is supposedly made for this
 
JRE
1:56 PM
It may not be faking it. A high pass filter would do that to a square wave. A high pass filter is a differentiator.
 
Wouldn't it just do two spikes at different locations?
When the square changes form
Anyways
 
JRE
A spike at each edge. And, the circuit diagram is available. There's nothing in there to fake a signal. Just a high pass and other filtering. No suspicious anything.
 
Ah okay. Well that's good to know then
 
2:55 PM
I have a task function triggered by an event on my micro controller. I turn an LED on and off at both ends of the function to signify it did something. Of course this time is so short the LED barely lights up at all. I don't want to introduce an artificial delay.
Is there any way I can get it blink "bright" enough without a delay
I was thinking I could put a capacitor in parallel with it to make it last longer. But that won't really work because the capacitor probably won't charge enough in the short time that voltage is increased.
I imagine it won't really work at least.
 
JRE
Some kind of timer controlled blink, I expect. Turn on the LED at the beginning, tell a timer to turn it off at the end of the method. The timer then handles the delay.
Or get all old school on it and trigger a 555 in one shot mode.
 
3:23 PM
@JRE I don't have a 555. Maybe I can borrow one
(from the lab)
 
JRE
Or get all meta on it, and program an Arduino Nano (or a PIC or other small controller) to read one digital input and generate a fixed length blink. :)
 
Well I used to do blinks with a dedicated task on my micro controller (it handled all LEDs). But was wondering if there was a "simpler" way
But yeah to do it analog I would probably need some kind of oscillator setup.
 
JRE
What is that icon you use? Is it the face of a seal, or is it a stick figure drawing of two people bumping fuzzies?
@Micrified: What is your icon?
 
3:58 PM
@JRE It saddens me you ask this
It's the cutest ghost ever
 
JRE
Ah. Hard to tell from the small version that is shown here in chat.
 
Your picture looks like some kind of weird signal
 
JRE
@Micrified My icon is in fact a picture of the inside of the roof of my garage as seen by 12GHz microwaves.
 
4:15 PM
I was going to say it looked like ceiling lights
almost
 
JRE
There is no light source or light fixture in the picture. The brightest parts are the wooden beams. Those are the diagonal lines in the picture.
 
Did you take the image with no lighting in the garage?
As in using it like a sort of vision camera
Obviously I shouldn't expect to see visible light. But just asking if you used it to "see" in the garage without visible light
 
JRE
There was light from the windows, of course, so I could see while I was working. The "camera" I used can only "see" microwaves. It can't see most lights, unless they are hot (blackbody radiation emits some microwaves) or from fluorescent lights.
Fluorescent lights emit broad band RF, that goes way up the scale.
 
How much range does it have, being so high frequency
 
JRE
It took like 20 minutes to make that picture. Far too slow to use as a sort of "night vision" system.
 
4:26 PM
ohh
 
JRE
Range is infinite. It doesn't transmit anything, it only receives. I have a picture somewhere of the moon made with my microwave camera.
 
I mean don't high frequency transmitters generally have high attenuation
 
so any returned signal is much weaker? I don't know anything about it tbh
 
JRE
It doesn't have a transmitter. It is totally passive.
 
4:28 PM
Ah, is that why it took so long?
It just sat and waited for microwaves to bounce around and hit it?
Anyway's it's pretty cool
 
JRE
It took so long because it only has one "pixel" and it has to be aimed around to collect the 14400 pixels in the image.
 
ah
Was going to ask how on earth you had the patience to aim that thing. But
"It has two heavy duty servo motors like you will find in remote controlled cars. It also has an RF level detector to measure the microwave intensity. The whole shebang is driven by a simple Arduino program that reads the RF level using a 24 bit analog to digital converter, drives the servos, and switches the various bands and polarization options that a satellite TV LNB provides"
I see how now
 
JRE
The original idea came from someone who really did spend hours making one image by hand.
 
 
5 hours later…
9:51 PM
@Micrified Are you using Right Leg Drive??
Also, what are you using for electrodes? You might try electrode gel, if it's a dry electrode, or even abrading the skin slightly.
 

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