Android Phone Based Metal Detector - FCMD

[moodz]

Ad1256 It's a very slow chip)))

I am using the DG411 switch to demodulate to baseband.
Baseband for a metal detector is about 1 hz to 15 hz
30 ksps is actually way faster than you need to sample 15 hz.

[JoyJo]

The ADS1256 ... is very cheap for what it is. It can easily achieve 19.9 ENOB ( thats 20 bits error free ) at 1000 SPS with the software I have developed.
Modules are available on PCB for around $10 au ... easier than falling off a log.
Using a switch like the DG411 as the demod 1000 SPS is way above what we actually need to fully extract the I and Q.
You can power the DG411 class switches upto +/- 22 volts or 44 volts single ended so its rugged.

Ad1256 It's a very slow chip)))

[moodz]

What is its role there?

It broadbands the output .. the load is still tuned but if you go off frequency its not as sensitive as a "standard" E class amp to detuning which causes power loss.
So you just change one cap to change frequency ...use relays or similiar.

[ivconic]

I like it Paul!
Except that I don't understand the "T1"?

What is its role there?

[moodz]

Yet another rebuild of the interface ... there are alot of controls on this detector (16+ ) but now focussed on simple military style utility.
No gimmick screens or wackydoo multiple page ..where is that control gone.
One screen, one glance, one control ( slider ). Push a button and adjust with slider.
Big buttons for gloved hands and the current value of that control is written on the button.
Velcro the display to your sleeve or mount on the control stick. Totally simple.

[moodz]

The ADS1256 ... is very cheap for what it is. It can easily achieve 19.9 ENOB ( thats 20 bits error free ) at 1000 SPS with the software I have developed.
Modules are available on PCB for around $10 au ... easier than falling off a log.
Using a switch like the DG411 as the demod 1000 SPS is way above what we actually need to fully extract the I and Q.
You can power the DG411 class switches upto +/- 22 volts or 44 volts single ended so its rugged.

[moodz]

clue 2 ... LOL

[moodz]

Ivica to answer your question T1 is found in just about every electronic appliance

[moodz]

Here is the intial ESP32 based schema ...we use an external "best bang for buck" ADC and a tricksy way of getting the IQ for VLF.
The sampling method can be used for PI or VLF ... just changeout the TX.
This will also be the basis of MAGPI V4.

[moodz]

The FCMD is a single frequency detector ( unless the TX does frequency switching ) in its simplest form.

I have now ported all the code to the ESP32 platform from the stm32H7. Considering I only started this yesterday its a good result.
The reason for this is that the H7 is overkill once you swap to an external ADC. The ESP also integrated dual mode bluetooth for Android and simultaneous audio.
FreeRTOS runs nicely and does all the housekeeping. The ESP32 is arguably more available and cheaper than the H7.

Should now be able to build a full detector from minimal parts. I am using an external ADC ( ADS1256 ) with the ESP32 and it achieves a verified 19.9 bit ENOB using my DirectIQ method to recover the I/Q stream.

An android app is used to fully control the Detector and the audio is available as 100Khz PWM on an ESP32 pin and 44.1 Khz @ 16bit audio on bluetooth.

Because all the controls are bluetooth based, the whole detector will fit into a very small plastic box that can be potted so its waterproof.
It will also be extremely light ( think 100 grams for the control box )
The code supports VLF and PI ( not at the same time ).

Running all the DSP / audio / bluetooth etc hardly cracks 30% utilisation in the ESP32.
Its all coded in C and runs under FreeRTOS internally.

TODOs ... add VDI display ( its in the DSP .. just not on the android )

My costs for hardware : ESP32 = 5 $AUD. 24 bit ADC board = 10 $AUD. TX/RX frontend ( 1 mosfet, 1 opamp, jellybean parts ) = $10 ... most of that is the low noise opamp.

So maybe 20 - 30 $AUD for one off ... just add a coil stick and battery ... most ppl have the phone.

There is only one small fly in the ointment. The DSP method is patented. So that cannot be given away for free. ( so lets add $10 for a one off non commercial licence fee ).

[moodz]

... all these parts are working in version 1. Just needs to be packaged now.

[moodz]

It would be nice if the FCMD just runs off 5 volts ... then we can use commodity 5 volt power packs for batteries etc.

Just testing the STM32H743 ... with all the DSP running it draws 170 ma from the 5 volt supply. ( the board uses a linear 3 volt supply regulator - we could implement a switch mode here)

power wise for the CPU that is 0.17 amps x 5 volts = 0.85 watts.
The transmitter takes 240 ma @ 5volts which goes into a switch mode supply to power the driver @ 1.2 volts.
240 ma @ 5 volts = 1.2 watts. The transmitter takes 850 ma at 1.2 volts = 1.002 watts so my 1.2 volt switch mode supply is 1.002/1.2 = 83.5% efficient.
So the total power drawn by the detector will be 0.85 + 1.2 = 2.05 watts.
I have a little 5 volt jellybean usb power pack here ... the spec on the back says 5000 mAH / 18.35 watt hour. DC 5.0 volts ( its regulated ) 2.00 Amps max and
you can almost hide it in your hand.
That means the detector will run for 9 hours on this pack ( all of $10 in Kmart ) and thats with 150 volts pp and 1.8 amps pp in the coil.

I would expect we will be running the detector off the battery pack most of the time .. however the name of the detector is Fone (sic) Connected Metal Detector ( AKA FCMD )
..so the question is can it be run from the phone USB port ( the software can talk through the USB port on the chip .. that is how I do all the telemetry to a PC )

Here is the AI summary ...

A modern smartphone with a USB-C port can reasonably supply between 2.5W and 7.5W (5V at 0.5A to 1.5A) to external peripherals via USB-OTG (On-The-Go) mode. While some high-end devices, particularly those with Samsung DeX capabilities, can output up to 15W (5V/3A), this is not typical for most smartphones.
Here is a breakdown of realistic power output capabilities:

• USB 2.0/OTG (Older/Budget phones): Generally limited to 5V at 500mA, or 2.5W.
• USB 3.0/USB-C (Typical Modern phones): Usually capable of 5V at 900mA–1.5A, resulting in 4.5W to 7.5W.
• Samsung Galaxy S/Note Series: Some can output up to 15W (5V/3A), enough to fast-charge another phone or run a portable USB hub.

Factors Influencing Power Supply:

• Battery Drain: Phones are not designed as primary power banks. High power draw will significantly drain the phone's battery.
• Thermal Constraints: Providing higher power generates heat, which can cause the phone to limit the output to protect its internal circuitry.

So the answer is YES for a phone with USB-C or older types because the detector power consumption at present is 2 Watts. ( and may improve slightly )
That means the detector will run off the USB of the phone ( which will be hosting the control panel app ) in a pinch.
Thus it is a true phone connected metal detector.
Free Lunch No 1



I did note that if the voltage drops to 4.3 volts .. the TX stops ( the CPU keeps going ) probably due to minimum supply on the Mosfet switch and/or driver chip
or it could be the 1.2 volt switchmode ... hmmm.
... this is not an issue because the battery pack maintains 5 volts till discharged.
Free Lunch No 2

moodz

[moodz]

Hey Moodz, I looked at your post again.
I would use a lot fewer elements from your circuit in the "E" amplifier circuit.
I personally, would use only the following elements:
-L1;
-Q1;
-C1;
-Cs ;
-LT ;
I would drastically increase the value of L1 to achieve a relatively constant smooth/non-pulsating DC consumption (this is one of the most important things), would choose Cs and LT for the required frequency and in accordance with RLT - possibly a higher quality factor (the other important thing) and, of course,the shunt capacitor C1.

That what you are offering is realy new and innovative in metal detecting.
I sincerely wish you success.

thanks bc .. I have moved on from that circuit ... but like cats theres more than one way

[boilcoil]

Hey Moodz, I looked at your post again.
I would use a lot fewer elements from your circuit in the "E" amplifier circuit.
I personally, would use only the following elements:
-L1;
-Q1;
-C1;
-Cs ;
-LT ;
I would drastically increase the value of L1 to achieve a relatively constant smooth/non-pulsating DC consumption (this is one of the most important things), would choose Cs and LT for the required frequency and in accordance with RLT - possibly a higher quality factor (the other important thing) and, of course,the shunt capacitor C1.

That what you are offering is realy new and innovative in metal detecting.
I sincerely wish you success.

[moodz]

doh .. spent 2 days chasing a faulty earth ( on and off ) on an ADC board and 20 minutes integrating the code into the FCMD to prototype the new ADC demod test.
The pic below shows the AD7177-2 chip on the bench connected to the stm32H743 and streaming from the USB port to a python plotter in the PC.
I going to test a demod method using this chip instead of using the 16 bit internal ADCs.