Hello,

Do you intend to use C3 and C5 in parallel?
Both are 100 nF.

Bertus

 

Do you intend to use C3 and C5 in parallel?
Both are 100 nF.

Hadn't thought of it that way. C5 is very near the microcontroller to filter it's input kinda like C4 is very near the op amp to filter it's V+. C3 is part of a LPF along with R5. Maybe I can omit one?

 

I don't think C1 is polarized, but the polarity you show should be reversed with negative at the input.

 

I deleted my post because I missed seeing some posts.

 

We've made a lot of good progress in the last couple weeks. My partner has the Q DSP Library frequency detection and 1 EU filter algorithms working, then displaying on the ESP32 onboard OLED screen using LVGL.

Hardware wise, I have some prototype PCB's that use a 7805 regulator, a LM358 op amp and a bandpass filter to condition the guitar signal into the ESP32. A schematic is listed in the Github /assembly folder.

The algorithm seems to work well at most any gain. I have a 100k pot installed that allows the gain to be anywhere from 1-24. It seems to work equally well with any gain >5. @panic mode suggests in another thread that clipping isn't necessarily a bad thing since we don't care about amplitude, only frequency.

You can see a video below. Github project link. Thanks to all those who have helped me so far!

 

One of the concerns I have is that guitar pickups can have a wide range of voltages... from 50 mV to a couple of volts. ESP32 ADC has a range of 0-3.1v and the voltage offset applies is 1.55v, so it's very possible to get outside that range. The setup seems to handle clipping reasonably well, but I was wondering if it would be possible to use the other side of the LM358 as a limiter. I found this article and downloaded the Spice file, but can't figure out how to make it work for a single sided supply.

An Op-Amp Limiter: How to Limit the Amplitude of Amplified Signals - Technical Articles (allaboutcircuits.com)