Noob wishes for some input on schematic

[hthulin]

(Unable to find the intro post on posting in the schematic forum I hope I'm not breaking any rules)

Wanted to make my own metal detector. Have some knowledge with micro-controllers but a noob when it comes to the analog parts .

Before I go ahead and etch the PCB I thought I'd check too see if anyone might have suggestions on how to improve this design? Perhaps it's missing something that might affect its long term performance etc?

The preamp is stolen from the "Blind Squirrel". Thought it might make things easier as it doesn't need a negative rail. Not sure how it affects performance.

Right now I have this bread-boarded and it seems to work pretty good. This schematic is at an early stage and is missing some control inputs and decoupling caps for the micro-controller.

Pin 26 outputs a PWM-signal and pin 24 is the ADC input. Sampling with at an aprox. ~2us interval to measure the slope.

Here's a video of the oscilloscope (yellow measured at R5 and blue Q1 pin 2):

https://youtu.be/UB_papsMJv8

Yellow line is shaking a bit but might be because it's breadboarded and picking up a lot of interference from the room? Also the ADC-sampling is visible by a slight voltage drop. Wonder why?

Any input would be greatly appreciated .

/H

[Teleno]

For the preamp, instead of one stage with a high gain N use two cascaded stages with sqrt(N) each. It greatly improves bandwidth.

[hthulin]

For the preamp, instead of one stage with a high gain N use two cascaded stages with sqrt(N) each. It greatly improves bandwidth.

Thanks for the input! Will look into that and do some further experimenting

[hthulin]

Thought I'd update this thread. Project has been stalled for a while due to the arrival of a new family member .

Changed the schematic slightly, removed some unnecessary components and the trimpot was set in series between mosfet driver and mosfet instead of tied to ground. Have yet to enhance the opamp design, but as it is now it's not very good.

Added a cheap 1.3" eBay OLED module to be able to monitor values for debugging.

Looks pretty neat with the histogram (the change is due to me waving a metal object).
https://youtu.be/fp63lRCSH4o

Here's one with sampled ADC data:
https://youtu.be/AD_ksnVOsBc

I noticed the signal gets very noisey late at night. Perhaps something with the atmosphere? Street lights (live in the city)? Maybe the breadboard acts as an antenna?

[6666]

looks interesting keep going

[bernte_one]

i dont know the datasheet of the Controller, but i thing you should add same capacitors at oscillator