WMD Geiger Counter - [gut shots]

General documentation, gut shot, schematic links, ongoing circuit tracing, deep thoughts ... all about boutique stompboxes.
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Post by devastator »

Arduino plateform is a good start for programming µC
yep , I'm waiting for an arduino board ordered last week. I started studying some exemple codes available.

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Post by andrej »

any interest? i can program all of it pretty effortlessly and even a couple of interesting additions (a user-set bitmask with a 8DIP switch, with selectable bitwise operations - or, xor, and, not) in quite a short time and with a DIRT cheap chip (through-hole, too!). i'll do the analog part, too. all open source and DIY only.

if we want a good clone, I'd need some of the work done by you guys, since I don't have the pedal.
i understand there is some kind of a gain stage in front with massive gain. i guess there is hard clipping at the end of it, used to limit the signal before the ADC. there also seems to be a filter at the output. could someone trace that? i don't care about ADC/DAC/uC/EEPROM, since I'll redo all of it the way I like it, just the gainstage and the filter. alternatively, I can slap on a basic non-inverting opamp gainstage with massive gain on tap and a couple of diodes (or zeners) to ground and use a tilt tone control ('AMZ presence control') after the DAC.

the other thing is that they replaced the hi-res waveform pdf on their website with a really low-res one. does anyone have the original version?
i can, actually, recognize most of those functions, and calculate them for [0..255] values, to use as look-up tables.

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Post by devastator »

that could be a neat project ! but instead of copying why not creating something new and go further ?

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Post by Space Jm »

Hello Andrej,

I got the geiger, but it is quite difficult to trace it because there are a lot of smd parts, dble pcb layers... I can tell you the global electronic architecture, it is easy to re-do something similar :

in > classic 1 single 2N3904 buffer > AOP TL071 : gain amplification classic stage > ADS 7816 AD >µC ATMEGA 644 > TLC 5615 DA > out

The display is a kingbright DA03 - 11 SRWA
The quartz is a ZTT 16.00MX resonator
gain 500ka
tone : 25kb
bit : 10kb
vol 50ka

They most difficuts things for me are :

- once the guitar signal goes inside the µC, how it is combine with the wave forms ? : addition ? integration ?
- This projects needs a big µC with a lot of memory (waveforms) and in/out to drive the display
- The project require SPI lines to drive the 5615 and I guess serial lines for the 7816

Nice stuff :)

I can give you more informations if you want
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Post by andrej »

Well, you've cleared up for me everything i needed.

It's not mixed, actually.
Every 8bit sample is a number (0 - 255 or -128 - 127). That's the way you get it from the ADC.
When you load the preset, you just load the waveform into the RAM (from flash or eeprom), as an array of 256 bytes, each one representing the corresponding waveform value for every possible sample. And that's what you send to the DAC, as it, too, expects 1byte samples.

The memory needed for 1 waveform is 256bytes. for 128 of them, it's 32Kbytes. Alternatively, many of the waveforms can be calculated on runtime and put into ram, when a preset is recalled. The pots are easily read, and so is CV input.

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Post by Space Jm »

Hello Andrej,

Few remarks :

- If you need gut shots I can provide some with a very good quality.
- I can send to you the waveforms in a good quality (coming from the user manual) could you send me an PM ?
- For the buffer and AOP stage, the Tube screamer IN/stage with its tone section could be a good thing.
- On the Geiger there are no clipping diodes, the AOP OUT seems to go directly to the 7816 and feed it a lot !
- There is also a regulator for the µC : LM2931AZ5 Fairchild.
- Which plateform will you use to code ? Arduino ?
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Post by andrej »

i will be using an AVR microcontroller (i'll see if i can find one with enough memory AND with through-hole package; atmega or atxmega), with code written in C and compiled with avr-gcc. arduino is way too slow and has way too much overhead for this use.
it will be open source, non-commercial. you'll have to flash it with an AVR programmer, or buy the preprogramed chips from me (they will be less than 5eur more expensive than the non-programmed chips).

i will also be using an ADC and DAC chips, though i have yet to decide which.

the controls will be the same, but I'm considering using an 8-seg led bargraph, to replace the 2-digit display. the bargraph can be replaced with discrete LEDs (because then you don't need to drill a square hole) and will show the preset number in binary, for a personal touch. if multiple people think it's impractical, i'll use 7-seg digits, like the original. it's the same amount of work for me.

'AMZ presence control' is much more flexible than TS tonestack, and a non-inverting opamp is a better buffer/gainstage. the regulator doesn't really matter: any 5v one will do, this is pretty low-powered.

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Post by FiveseveN »

andrej wrote:it's the same amount of work for me.
For a binary display all you need is a binary counter, but for 7-segment you'll need two decoder/drivers, plus a counter or two, presuming you're going for a low pin count uC. Or am I missing something?
I for one love the binary display idea, I think it goes well with the theme.
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Post by andrej »

well, actually, i've done both before. dedicated 7seg drivers are expensive, so i use shift registers to do it. same goes for led bargraph. i have a library to communicate with shift registers already.

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Post by Buks »

I had a Geiger Counter. It was interesting, endless posibilities, but not realy useful as it could not store settings. Therefore I passed it on.

Dont know if its possible, but a useful addition to the original would be to add some way to store settings so they can easily be recalled.

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Post by andrej »

i thought about it. i could fit it into a 1590b, too, that way. use digital pots for the analog part, all that jazz, and input everything with a single pot and encoder. add presets, too.

it's just that i'm afraid it would be a bit user-unfriendly. and it would be logical to add a screen, and i don't know how to drill a rectangular hole in a diecast aluminum box... do you have an idea how to do it?

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Post by devastator »

the pedal format is fixed ? I thought it could interesting to implant the circuit is a rack format case with a remote footswitch. And if storage I guess some would like footswitch to access patches ect...

actually pedal format isn't really that good with big circuit :mrgreen:

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Post by FiveseveN »

I think the format should be the least of our worries at this point. Once the basics are worked out it would be trivial to add presets (since you already have a uC in there), different interfaces, MIDI etc.
Space Jm, have you identified the rest of the TL071 gain stage? What is the maximum gain and does it employ any significant filtering?
andrej, have you figured out how they vary the bit depth and sample rate?
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Post by Space Jm »

FiveseveN wrote:I think the format should be the least of our worries at this point. Once the basics are worked out it would be trivial to add presets (since you already have a uC in there), different interfaces, MIDI etc.
Space Jm, have you identified the rest of the TL071 gain stage? What is the maximum gain and does it employ any significant filtering?
andrej, have you figured out how they vary the bit depth and sample rate?
No I did not trace the TL071 part, too many vias, smd and 2ble sides pcb, this make the reverse thing difficult to do. As fare as I can see there are 5 or 6 components around the TL connected with a 500k pot.

It is a classic OAMP amplification.

To drill a rectangular hole in a box, you need a milling machine, but it is very expensive.

Anyway, it seems possible to use a classic "drilling" machine as a milling machine with a special X/Y table, this one seems expensive but it is possible to get a cheap one for 100€ :

http://www.hellopro.fr/table-croisee-30 ... oduit.html

- You press the box on the X/Y table.
- You drill a classic big hole in your rectangular area, for instance 12mm (smaller then the rectangular area for sure).
- You put a special tool (for milling) in you drilling machine.
- You put the milling tool inside the hole
- Then you move in X and Y directions the table to remove aluminum and build the rectangular hole.

I have never try...but I will do.
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Post by andrej »

FiveseveN wrote:I think the format should be the least of our worries at this point. Once the basics are worked out it would be trivial to add presets (since you already have a uC in there), different interfaces, MIDI etc.
Space Jm, have you identified the rest of the TL071 gain stage? What is the maximum gain and does it employ any significant filtering?
andrej, have you figured out how they vary the bit depth and sample rate?
yep, pretty much.

bit depth is varied by using 'bitwise and' with bitmasks of 0b11111111 (8 bit), 0b11111110 (7bit),... , 0b10000000 (1bit)
sample can be varied in several ways. for example, setting the clock interrupt for a really short duration and then varying on how many of the clocks you sample...

i've devised a simple (1 cheap micro + serial interface) rig to rip the original waveshapes from the geiger counter. Space Jm, are you interested in building it? that would be the best way to replicate the device in its entirety.

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Post by Space Jm »

Hello Andrej,

Yes for sure I am interested to build it, at least to breadbord it first, what do you expect from me ?
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Post by andrej »

do you happen to have an arduino? because an arduino, an ADC and a DAC would suffice for this one-time use.

you'd connect the arduino with an ADC and a DAC on a breadboard. then, you'd connect the DAC's output to the Geiger counter, at the VERY (that exact pin) input of the ADC (a temporary soldering job). then, you'd connect your ADC to the VERY output of Geiger Counter's DAC

i'd write the code that would cycle between m and M voltage in (2^9/(M-m)) steps, where m is the minimum and M is the maximum voltage of ADC (we'll see in the datashet). each time the arduino outputs a voltage through the DAC, it samples it with the ADC and sends that info through the serial port to the computer, where you will be running a serial listening program. you just copy/paste that data into a text file, then change the preset, and repeat the process. in the end, you send me the file, i average the data (because we used 2^9 different levels, which is twice the Geiger's resolution) and get the correct wavetables.

there is even a better way (i'd spoof the adc and dac completely with an arduino, so we'd get the exact digital data straight from the horse's mouth), but you'd need to desolder/disable the original adc in the geiger counter temporarily.

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Post by Space Jm »

Waouw, this is a james bond story :)

Yes I know to code in arduino, I can code encoder, 7 segments display , waveforms and SPI management of DAC, but with bif effort (I am not a golden Engineer).To be honnest, your method seems a little bit too complex for me :).The method will need to write a code to make the ADC and the DAC work on the breadbord, I am not sure to be abble to do that.

Anyway, why dont' you want to write the waveforms ? I know how to do that in arduino, and I think we may not need 256 presets. I think it is really too much, most of them are very close. 50 ou 100 can be sufficient.
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Post by andrej »

you wouldn't have to write anything, i'd do it. you'd just have to flash the code into an arduino it and connect it to the pedal as i suggested. this is the only way to get a 1:1 clone.

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Post by Space Jm »

ok understand, I will do !
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