Let's make a closely MXT like detector!

[KRinAZ]

That was an interim replacement for the 16C76, I think prices were going up so we swapped out for another chip.

Post #22 shows the old-style MXT/GMT board on the left, and the new style MXT/MXT Pro/GMT on the right. I switched all the caps and connectors to SMT, the processor is a 44pin QFP, and there is a new PCI edge connector for manufacturing. Sorry, don't know which micro, still a 16F PIC though.

Good to know, thx!

[KRinAZ]

The Racer was a hardware clone of the Teknetics T2, except that the T2 used and MSP430 and the Racer has a PIC24. The T2 was designed by David Johnson after he did the MXT, so it was basically an "MXT-2". That's why the Racer looks a lot like the MXT.

It's fascinating to me to find out all these behind the scenes goings on in the detector mfg world. Must be more competitive and cloak and dagger to work in the industry than a lot of us retail consumers realize...

[KRinAZ]

Here is a look at the pod. It uses a 74164 shift register for a serial to parallel convertor to drive the 16 x 2 LCD. You can also see a 555 timer and a CD4051 multiplexer.

Thanks for the schematic Ivica!

Hmmm, and thanks for posting these, looks like a pretty simple display to repair or possibly mod (backlight for one mod), and with that thought in mind the RevD control boards vs the RevE to me seem more repairable, and since Micro PIC16Fxxx's are still available and pretty cheap - genuine MicroChip ones run something like $2.70 USD in single quantities - a PIC with our own code could be tested in a RevD board by just plugging it in, before testing in a newly designed control board as well.

I'm starting to think of basing the electronics side of this project on a RevD MXT, instead of a MXT Pro. The MXT Pro's multiple tones are (I believe) simply in the code (I would prefer the MXT tones over the Pro, but that's just me), display backlight or a new display in the existing housing is probably a fairly easy mod, and as for Ground Grab, I suppose I've never had it so don't know what I'm missing, but have always been blissfully happy with the GB performance of the MXT as is. Also I'm happy with the functions of the trigger switch in the MXT (vs the Pro), anyone not?

Thoughts? anyone think there's anything about the RevE electronics that is must have? Anyone think Ground Grab is a must or very nice to have?

Edit - oh yes - actually the GMT has Ground Grab also, and I did use it when I had the GMT...

[Carl-NC]

That's interesting to know. Looking at the MXT schematic it shows a cycle time of 4ms for the adc. Would that be a single sample or for all the channels?

4ms will be the overall "loop rate" of the main processing loop. During each 4ms loop, you want to capture all the channels.

[Carl-NC]

Hmmm, and thanks for posting these, looks like a pretty simple display to repair or possibly mod (backlight for one mod), and with that thought in mind the RevD control boards vs the RevE to me seem more repairable, and since Micro PIC16Fxxx's are still available and pretty cheap - genuine MicroChip ones run something like $2.70 USD in single quantities - a PIC with our own code could be tested in a RevD board by just plugging it in, before testing in a newly designed control board as well.

I'm starting to think of basing the electronics side of this project on a RevD MXT, instead of a MXT Pro. The MXT Pro's multiple tones are (I believe) simply in the code (I would prefer the MXT tones over the Pro, but that's just me), display backlight or a new display in the existing housing is probably a fairly easy mod, and as for Ground Grab, I suppose I've never had it so don't know what I'm missing, but have always been blissfully happy with the GB performance of the MXT as is. Also I'm happy with the functions of the trigger switch in the MXT (vs the Pro), anyone not?

Thoughts? anyone think there's anything about the RevE electronics that is must have? Anyone think Ground Grab is a must or very nice to have?

Personally, I wouldn't use any 8-bit micro. You can easily get 32-bit micros dirt cheap that will run rings around a PIC, and with far more capable peripherals. I use STM32 micros in all my work projects.

Pretty much all the features you mention are software-based. The circuit boards for the MXT, MXT-Pro, and GMT were all almost identical (GMT had a different TX cap and minor changes to the preamp) but were loaded with different software.

[KRinAZ]

Personally, I wouldn't use any 8-bit micro. You can easily get 32-bit micros dirt cheap that will run rings around a PIC, and with far more capable peripherals. I use STM32 micros in all my work projects.

Pretty much all the features you mention are software-based. The circuit boards for the MXT, MXT-Pro, and GMT were all almost identical (GMT had a different TX cap and minor changes to the preamp) but were loaded with different software.

Ok, ok, I give haha and admit I'm clinging too tightly to the 20+ year old MXT technology. I can't seem to let go of the MXT so it's probably better if I direct my MXT cling in a new thread - focused on MXT mods...which I suppose I'll do soon...after searching what's already out there...

For the purposes of this project I have done various Arduino projects, and have the PCB on order for George's Arduino VLF project, but no projects on the ubiquitous STM32, so a couple Q's - I've heard of the STM32CubeIDE platform for coding, would that be recommended or is there another IDE to consider? And which chip programmer for the limited budget hobbyist?

BTW I use primarily Ubuntu LiNUX, have Mint and KUbuntu systems also but don't use them nearly as much. Definitely Debian based though. I use KiCAD, FreeCAD, ArduinoIDE, GCC, etc., on my Ubuntu systems. I see there is a version of STM32CubeIDE (free) and STM32CubeProgrammer (free) for Debian systems...and STLinkV2 ($22 USD at Mouser) for the hardware side...I'm sure there are other tools...& I'm sure this could be an entire separate thread but just some simple recommendations pls...or just use these tools?

[KRinAZ]

Something I noticed on the schematic - at TP13 (to the right of the Transmitter section) it shows a square wave with 72us duty cycle (13.888khz, for MXT?) but labeled 47.619khz (for GMT?) (duty cycle would be 21us)...hmmm...

Also it appears this signal comes from the PIC pin 13 (RC2/CCP1) labeled PWM1 - as a PWM output for the square wave for the TX/RX frequencies - under software control - and so could be manipulated as needed within the capabilities/response of the coil and TX/RX sections - and assigned to a new knob/control

Hmmm...maybe that is how the multi-freq White's systems work? and/or how the GMT interference avoidance freq shift works?

Having 2 freq's - at each end of the 90% points of a bell curve - would be an interesting mash for Prospecting at the high end and Relic at the low end, perhaps even C&J as a third in the middle?

It occurs to me - does the MXT do this now? I'll pass the coil over my scope lead, in each mode, tomorrow and observe freq's...

[Carl-NC]

Get STM32CubeIDE for programming. Get STM32CubeMX for assigning pins and generating start-up code. Both free. Chinese clone ST-Link programmers can be found on eBay for $3. Or, buy an STM32-Nucleo board with the micro you want to use and it comes with an ST-Link programmer that also works independently. That's what I use.

The MXT runs at 13.8kHz in all modes. The GMT runs at 48kHz. Yes, you could design a system to use radically different frequencies for different modes; say, Relic = 2kHz, Coin = 13kHz, and Gold = 48kHz. But the MXT (and GMT) uses a boosted resonance transmitter (L4, C18, C20, and the TX coil) that can only run at one frequency, so you'll need to do something different.

[moodz]

Get STM32CubeIDE for programming. Get STM32CubeMX for assigning pins and generating start-up code. Both free. Chinese clone ST-Link programmers can be found on eBay for $3. Or, buy an STM32-Nucleo board with the micro you want to use and it comes with an ST-Link programmer that also works independently. That's what I use.

The MXT runs at 13.8kHz in all modes. The GMT runs at 48kHz. Yes, you could design a system to use radically different frequencies for different modes; say, Relic = 2kHz, Coin = 13kHz, and Gold = 48kHz. But the MXT (and GMT) uses a boosted resonance transmitter (L4, C18, C20, and the TX coil) that can only run at one frequency, so you'll need to do something different.

I noticed the later versions of the STM32 software give a warning message about using cloned stlink dongles ( aka chinese ) and would not program the chip ... so I used to use the stlink that comes with most stm32 demo boards like carl said.
Although alot of the stm32 chips have a factory bootloader ... you just press reset then press boot button and release reset then the boot button and it puts the chip in fw download mode ... so no programmer needed at all. Its more convenient than a programmer.

[KRinAZ]

Get STM32CubeIDE for programming. Get STM32CubeMX for assigning pins and generating start-up code. Both free. Chinese clone ST-Link programmers can be found on eBay for $3. Or, buy an STM32-Nucleo board withe micro you want to use and it comes with an ST-Link programmer that also works independently. That's what I use.

The MXT runs at 13.8kHz in all modes. The GMT runs at 48kHz. Yes, you could design a system to use radically different frequencies for different modes; say, Relic = 2kHz, Coin = 13kHz, and Gold = 48kHz. But the MXT (and GMT) uses a boosted resonance transmitter (L4, C18, C20, and the TX coil) that can only run at one frequency, so you'll need to do something different.

Ok sounds good on the STM32 development platform, the STM software is the way to go then. I like the idea of the Nucleo board, didn't know they can be a programmer as well, nice.

While searching for Bluetooth solutions I came across the ESP32 and the Raspberry Pi Pico WH. They each appear to have pretty capable dual core processors. I'm wondering if they could be the microprocessor instead of just a shield for the Nucleo. I'm kinda thinking out loud here as I haven't gone over their datasheets for their I/O ports, A/D capabilities, and such. I'm thinking if they are not a suitable standalone micorprocessor then the ESP32 on a Nucleo could be a nice core to build around. Have to spend some time determining which Nucleo would be best... To me Bluetooth is important - I pretty much always detect with headphones, and am so done with the headphone cord! Actually earbuds would be far better than over ear IMO.

Thx for your input on the TX RX freqs. For now just single frequency. Once the project is mature perhaps multi-freq can be explored as a mod. As you said...start simple..

[KRinAZ]

I noticed the later versions of the STM32 software give a warning message about using cloned stlink dongles ( aka chinese ) and would not program the chip ... so I used to use the stlink that comes with most stm32 demo boards like carl said.
Although alot of the stm32 chips have a factory bootloader ... you just press reset then press boot button and release reset then the boot button and it puts the chip in fw download mode ... so no programmer needed at all. Its more convenient than a programmer.

Thx, very good to know...& yes just this evening I read about the bootloader and the boot button and all on the Nucleo's, quite handy! ... a little like an Arduino, super easy.

I'm interested to hear thoughts on whether the ESP32 or Raspberry Pi Pico WH (the one that's just a shield/hat) could take the place of the Nucleo and be the processor...

[KRinAZ]

OK so now I'm going to maybe open a huge writhing can of worms in asking all interested - stick with 13.8khz TX RX (as the single frequency)? Seems to work beautifully in the MXT and I'm happy with it.

I'd also be happy with skewing the freq higher to benefit Prospecting mode, but that would no doubt be to the detriment of the Relic and C&J modes, also that would complicate the availability of commercially made coils. I know Detech has nice DD coils for 13.8khz in addition to whatever White's Eclipse coils are still out there.

But thought I'd ask. If anyone suggests a different freq pls also give the pros and cons.

[moodz]

Thx, very good to know...& yes just this evening I read about the bootloader and the boot button and all on the Nucleo's, quite handy! ... a little like an Arduino, super easy.

I'm interested to hear thoughts on whether the ESP32 or Raspberry Pi Pico WH (the one that's just a shield/hat) could take the place of the Nucleo and be the processor...

open the attachment in a webrowser for a comparative view.

I am trying out the ESP32 on a VLF at the moment .. but that is with an external demod and ADC. If you go internal demod with a straight conversion ADC ( ext or internal ) then the STM32 wins handsdown.

[KRinAZ]

open the attachment in a webrowser for a comparative view.

I am trying out the ESP32 on a VLF at the moment .. but that is with an external demod and ADC. If you go internal demod with a straight conversion ADC ( ext or internal ) then the STM32 wins handsdown.

Wow!, now that's a comprehensive evaluation, invaluable, thanks. So it seems clear the STM32 wins. On the RPi I was actually thinking about the newer RPi Pico WH with Bluetooth, but looking at it I don't think it has the peripheral support needed, and probably is less suited than the RPi5 in the chart.

So now to look at Bluetooth modules for the STM32...I'm thinking a hat for the Nucleo would be an easy solution, I found
1) Bluetooth Low Energy expansion board based on the BLUENRG-M2SP module for STM32 Nucleo, supports audio?
2) Maybe the same thing? STM32WBA55G-DK AND STM32WBA65I-DK with audio stream support - this appears to be just what's needed
2) Infineon WiFi+Bluetooth for Nucleo by Murata, I don't see a need for WiFi in this project though

There may be other Bluetooth solutions to consider such as I2C connected Bluetooth modules...


EDIT - I see those DK's - development kits - are $86 each, a nice solution but a Nucleo and separate Bluetooth will be much less $$$
Also it appears the STM32H based Nucleos are discontinued, the STM32F, STM32G, and STM32L based Nucleos are current production according to the STM site. I'm just beginning to get educated on the differences and a good selection for this project...

A thought - if the 8 bit PIC running 8mhz was enough processor and resources to run the MXT it seems like even the slowest STM32 would be overkill - so is a H series really needed? Would the L low power / the least powerful be enough if there is one with the needed peripherals? It seems like all the STM32 variants have more flash and memory than will be needed, at least to my - still learning the STM32 lineup - mind.

I guess I need to make a chart of the specific resources the MXT uses of the PIC, then compare to the STM32 variants resources...to be continued...

[KRinAZ]

In post #42 I asked about search coil frequencies, now another possibly thorny question - coil types - to my knowledge most favor the DD coils over concentric on the MXT, saying better ground handling, target separation, and detection depth. The same would likely apply to this project and I propose the development and testing be done with White's Eclipse DD coils, and if anyone has other brand DD coils to test with that would be a bonus. Thoughts?