Let's make a closely MXT like detector!

[KRinAZ]

An update -

1) On the PIC Programmer - I have finally got the ancient PICStart Plus PIC programmer, and it's MPLab IDE, working, and have used it to burn (and then read) a PIC17C44 in order to do a firmware update of the PICStart Plus programmer itself. If anyone else decides to get one of these working this will save you hours of time - it (MPLab IDE v5.7.4, no newer version, no MPLab X IDE) requires either actual Win95 or a true Win95 emulation in Win10-x32 (but not x64) via NTVDM, directly on a PC with at least one of each - a real Com port (as Com1, 2, 3, or 4) and a real LPT port (as LPT1). The Win install cannot be in a VM (I tried VirtualBox) - as MPLab must have direct hardware access - no virtualization will work. Win98 is too new!!!, a true Win95 install, or true Win95 emulation must be achieved for the MPLab IDE to operate. Since I have largely avoided using Win for the last 25 years I had to really dig into old memories of using Win95 to get things working correctly...if you decide to try to get one of these old PIC IDE and programing platforms working - feel free to ask me Q's - especially which hardware version of PICStart Plus you would want...
.
The K150 PIC programmer was much easier to get working but doesn't have nearly the features the old MPLab does...

Turns out my MXT is an older version - has control board p/n 505-0224-C with an actual socketed PDIP PIC16C76 with marking 1.0 in pen (v1.0 of firmware) - I am under the impression 1.0 marking is MXT firmware and 1.1 marking is GMT firmware, both plugged into the same control board part number. In other words a GMT also has a control board of the same p/n but a different firmware. I believe Carl at some point also as made this point - relying on memory. Observing the schematic - the PIC firmware determines the TX frequency - I find it curious how the same board tunes either the 14khz MXT coil or the GMT 48khz coil...especially doing it so well...

I will apply my MPLab environment to my MXT PIC soon...


2) On the STM32 selection - the criteria I came up with:
a) Only LQFP packages - to make hand soldering realistic, preferrably LQFP32
b) There is a Nucleo board with the selected processor - so that breadboarding can be done on sections of the MXT instead of having to build the whole control board first, and then chunks of the firmware developed.
c) Select the highest end version of each of these
With these criteria there are two choices:
STM32F303K8T6 as LQFP32 - and it's NUCLEO-F303K8 dev board - in the NUCLEO-32 family.
STM32H503RBT6 as LQFP64 - and it's NUCLEO-H503RB dev board - in the NUCLEO-64 family.

Since the STM32F303K8T6 / LQFP32 will be much easier to hand solder I'm trying this first. My NUCLEO-F303K8 arrived today, and I rummaged around and found I have a LCD 4x80 I2C display, and a color touch screen I2C TFT display, so will begin with these (the LCD 4x80 first) as I breadboard bits of the circuit.

Processor comparison:


Current active component list:

MXT Active Components List v1b
U1 LP2951-50 SOIC8 100ma 5v LDO Voltage Regulator
U2 TLE2426 SOIC8 Voltage Reference
U3 LQFP-32 STM32F303K8T6 Microprocessor
U4 74HCT4053 SOIC16 MUX
U5 ADS8320 VSSOP8 ADC
U6 74HC4351 SOIC20 MUX
U7 TLV9362 SOIC8 Dual Op Amp
U8 LTC1446 SOIC8 DAC
U9 TLC555 SOIC8 Timer
U10 TLV1842 TSSOP8 Dual Comparator
U11 TLV9362 SOIC8 Dual Op Amp
U12 TLV9362 SOIC8 Dual Op Amp
U13 TLV9362 SOIC8 Dual Op Amp
U14 TLV9362 SOIC8 Dual Op Amp
U15 LP2951-33 SOIC8 100ma 3.3v LDO Voltage Regulator - added - to power STM32
Q1 MMBT3906 SMT PNP BJT
Q2 MMBT3906 SMT PNP BJT
Q3 MMBT3906 SMT PNP BJT
Q4 MMBT3906 SMT PNP BJT
Q5 MMBT3904 SMT NPN BJT
Q6 MMBT3906 SMT PNP BJT
Q7 MMBT3904 SMT NPN BJT
D1 IN4148
D2 IN4148
D3 IN4148
D4 N/A
D5 IN4148
D6 N/A
D7 IN4148
TH1 10K NTC Thermistor
X1 WAS 8mhz
X1 NOW 16mhz? 24mhz? 32mhz?

[KRinAZ]

That looks reasonable. Often I lay out the preamp for thru-hole, then use an adapter board to plug in an SMT opamp.

Great idea on the adapter board - thx.

Are you using an Hitachi-style alpha-numeric display? Many of those are daylight readable and include a backlight.

I agree - a Hitachi display with (added) ambient sensing backlight (that could be turned off) would certainly work and fit right in with the MXT. Lots of options to choose from, TBD

[Carl-NC]

I'm thinking the TLV9362 opamp (successor to the NE5532) would be a good replacement for the MC33077 and MC33178.

That looks reasonable. Often I lay out the preamp for thru-hole, then use an adapter board to plug in an SMT opamp.

The display (I'm thinking a daylight and low light fully readable) - TBD

Are you using an Hitachi-style alpha-numeric display? Many of those are daylight readable and include a backlight.

[KRinAZ]

A quick note - at times I may be quiet for a day or three as I have some other projects going on also, work on this project is still going along.

I'm going to start on a KiCAD schematic, starting at the PS section...and don't plan to worry about the Bluetooth or display sections until the main schematic is completed.

And, all my PIC stuff is supposed to arrive by this Sat 4/25 - those old programmers, a K150, a batch of ten PIC16C76's to torture and experiment on haha, and such...

Onward thru the fog...

[KRinAZ]

Opamps are not a problem, lots to choose from even in thru-hole.

I'm thinking the TLV9362 opamp (successor to the NE5532) would be a good replacement for the MC33077 and MC33178.

Anyone think otherwise, or suggest a more suitable replacement?



The only other component questions (that I'm currently aware of) are:

The specific STM32 - I'm thinking one of the H7's - TBD

A bluetooth module - TBD

The display (I'm thinking a daylight and low light fully readable) - TBD

[KRinAZ]

Ok just a quik note - I think I'm willing to give SMD - for chip devices - a go.

I found a youtube with a guy using soldering tools very much like mine, soldering STM32's and such on his bench, I think I can pick up his method / skill. Still thinking thru-hole for resistors, capacitors, (passives), and diodes, and maybe transistors (just because I and probably you - already have tons of them), and SMD for all chips (with pads that make it easy to check for pin continuity and for bridges) - I may have to make the KiCAD pad footprints - that's ok with me.

[Hristo]

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 series LC resonance transmitter (L4, C18, C20, and the TX coil) that can only run at one frequency, so \

you'll need to do something different.

like old Bulgarian Golden Mask 5 (like Mambo No.5 song of Lou Bega)

[Okelm]

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.

[Carl-NC]

Opamps are not a problem, lots to choose from even in thru-hole.

[KRinAZ]

...My good soldering iron is a Metcal MXPS-5200...

Hmmm...I'll have to watch for a deal on a Metcal MXPS-5200...

[KRinAZ]

...In the MXT the biggest problem chips will be the micro and the ADC, and maybe any switching regulators. A Nucleo board solves the micro but it can be big. You can usually find eval boards for ADCs but they are often not all that friendly for incorporating into a design and are often expensive. So, most likely, you will be stuck with an SMT ADC. Same with switching regs, but fortunately it's easy to find one in 5- or 6-pin SMT that's easy to solder.

Another potential solution is to have the board house install the difficult parts. I've ordered fully built boards from JLC; their minimum order is 2 and their part pricing is quite good...

Something I have in the back of my mind also. If SMT can't be avoided, this would be an option for folks like me, and there are certainly those of you who would be quite comfortable soldering the SMT components.

But first I'm going to explore thru-hole possibilities...more soon...probably tomorrow...

[KRinAZ]

Regarding:

U5 ADS8320 ADC AVAIL SMT ONLY Mouser DigiKey - I will search for a thru-hole replacement.

U11 MC33077 Dual Op Amp NOT avail Mouser DigiKey Obsolete
U12 MC33178 Dual Op Amp AVAIL SMT ONLY Mouser DigiKey

Back when I built George's MiniPulse Plus PI project, I did some mods to it including cleaner opamps. I'm going to go back to my notes and remember the succession of opamps I tried and see if I can find suitable replacements for the MC33xxx's. These will require close scrutiny to get right as they are crucial parts of the Receive chain.

More soon with replacements and feedback on all of the pros and cons...remembering we are not wanting to mod the analog circuits, just complete the parts list with thru-hole, and available, parts.

[Carl-NC]

Would you be ok with us just using a 2N3904 for each NPN and a 2N3906 for each PNP - throughout - then?

Offhand I don't see any problem with that.

[Carl-NC]

Although all my work projects are pure SMT, I still do a lot of thru-hole designs, especially smaller test circuits where I want to easily swap components. Even with a bad soldering iron (and my Weller fits in that category) I can usually solder 0805 passives and SOIC. My good soldering iron is a Metcal MXPS-5200 and I can do 0402 passives and most QFPs. In the past I've replaced QFP-80 STM32's but it's painful. There are other tricks like using solder paste and a heat pencil, I've used that to install QFN parts. (I work remotely from FTP so if anything needs to be done, I'm the only one to do it.)

In the MXT the biggest problem chips will be the micro and the ADC, and maybe any switching regulators. A Nucleo board solves the micro but it can be big. You can usually find eval boards for ADCs but they are often not all that friendly for incorporating into a design and are often expensive. So, most likely, you will be stuck with an SMT ADC. Same with switching regs, but fortunately it's easy to find one in 5- or 6-pin SMT that's easy to solder.

Another potential solution is to have the board house install the difficult parts. I've ordered fully built boards from JLC; their minimum order is 2 and their part pricing is quite good. You still have to pay a set-up and build fee and depending on how many parts you install it can get pricey. The last board I built was about 2x more complex than the MXT and 5 boards cost $840.

[KRinAZ]

...For example, FMMT4403 is the same as MMBT4403 (SMT) and 2N4403 (thru-hole)...

Ok that just got my attention - didn't know to just strip off the prefix and search for the number or more the generic mmbt / 2N versions - that's very good to know.