Android Phone Based Metal Detector - FCMD

[moodz]

AI will give you all sorts of great answers .. but the proof is in the pudding ( or is it the eating ? ).

Anyway here is the frontend response for my sampling scheme from the C code.
The nulls are really sharp mains reduction wont be infinity obviously due to variance in mains frequency.

[moodz]

regarding the loop rates ... 50 Hz is actually better than a fast loop rate.

Below is the comparison of continuous target, 200 hz rate, 50 hz rate and my code cubic interpolation .... giving a smooth signal response that is "near perfect".
If you make your loop faster than needs be for a given target bandwith its just ignoring basic nyquist sampling and shannons sampling theorem.

[Hristo]

This real math science is really trhiling a me amuzment by da way is not correct on target signal response it is not a continius signal so ewretinlg later is no relevant sorry to upset you again tell you just use 250SPS and all be well , and everything will be fine, and you'll be bathing in a chocolate bath.

[moodz]

This real math science is really trhiling a me amuzment by da way is not correct on target signal response it is not a continius signal so ewretinlg later is no relevant sorry to upset you again tell you just use 250SPS and all be well , and everything will be fine, and you'll be bathing in a chocolate bath.

LOL. I am bathing in a chocolate bath ... the signal is just samples .. mine come in at 50 hz ... the integrators fully reset every 20 ms ( ie every cycle ) so theoretically it can detect a target in 20 milliseconds ..

OK how about I put variable loop rate control in ( just for you )

[Carl-NC]

Below is the comparison of continuous target, 200 hz rate, 50 hz rate and my code cubic interpolation

Your Gaussian curve looks slower than it should for 15Hz. This is what I come up with for a 15Hz target response sampled at 50Hz:


In general, the more you sample the more you can filter. The only reason most detectors used a 5ms loop rate is that processors of yore couldn't do much more than that.

[moodz]

While everyone is considering if AI can write production code or not ......

The simplest possible version of the FCMD ( fone connected metal detector ) is a STM32 processor and a single mosfet + some resistor / cap / coils etc.

The STM32 processors have a DFU mode for loading firmware ... its a factory firmware update mode and it makes "bricking" the CPU almost impossible.

By bundling the latest firmware with the android app the firmware can be loaded over the usb port from the Android app. No need for programmers or flaky bootloaders.
The transmit circuit uses my modified E class driver using a single mosfet and gets around 1 amp peak to peak in the coil from 1.2 volts. Current consumption from a 5 volt source is around 200 mA ( total ).
So its possible to have a detector electronics enclosure that is the size of a matchbox that you just plug your phone USB into and you are ready to go.
Audio comes from the phone as do all controls and power ( but can run off other power if required ). If the usb is disconnected and the box has aux power the audio falls back to PWM.
The phone provides audio from internal loudspeaker or Bluetooth. Maximum latency is 20 ms.

I am doing the preship tests prior to going live on playstore ... using AI of course.

[moodz]

This is the SDR of metal detectors .... ultra simple circuit mostly change code to do what you want at what frequency etc etc.
You can build one under an hour for $10 - $20 .. dont even need a PCB.
All of the complexity has moved from the hardware to the software.

At this time the app supports any stm32h743 with a USB connector.

more frontends coming soon for PI DD, monocoil PI, monocoil VLF, monopolar, bipolar ....

Ferinstance emulating a classic whites MXT detector is trivial.

[Aziz]

Hi Paul,

this is really nice, the more KISS, the more