Let's make a closely MXT like detector!

[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.

[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...

[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?

[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.

[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.

[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...

[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]

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!

[Altra]

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.

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?

[Carl-NC]

A partial schematic of the Makro Racer was posted here on the forum a while back. One of the members here claimed it was a copy of the MXT. Looking at the two schematics the Nokta engineer did duplicate many parts from the MXT.

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.

[Carl-NC]

If it helps any, in that pic that ivconic posted of a MXT PCB (probably a later revision PCB) I'm guessing it to have a 28 pin PDIP MicroChip PIC16F886...

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.

[Altra]

A partial schematic of the Makro Racer was posted here on the forum a while back. One of the members here claimed it was a copy of the MXT. Looking at the two schematics the Nokta engineer did duplicate many parts from the MXT.

Makro Racer

[Skippy]

[deleted]

[Altra]

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!

[KRinAZ]

MXT & GMT, approx 60-70% of the layouts are quite the same.

Interesting to compare the 2, also interesting the information present on the MXT board e.g. looks like the connector near the center marked P00 (I'm guessing) goes to the display, and if so that it's probably a SPI link, and that the toggle switch under the display probably also goes through that link (still guessing) - update - after looking at the schematic and PIC16C76 data sheet, looks like neither I2C nor SPI is used, but some unique coded serial method (still guessing though).