Rockdude discusses precision rectifiers and positional sens

[ignotus]

I have a few questions about dimitris schematic:

ground.jpg

Are all the nets/lines with this symbol supposed to be connected together and go to ground somewhere?

Yes. You connect them all together and then you run a cable to the ground in your MD; e.g. to the sleeve of any of the input jacks.

power.jpg

And all the nets with this symbol are supposed to connect together and go to power somewhere? To power on my synthex board or somewhere else?

Yes, same as ground. It then goes to +5v in your MD; e.g. the power source for the hi hat pedal (you can take it from the hi hat jack).

powerconnection-1.jpg

Is this some kind of isolated part of the schematic? It's not connected to the rest as far as I can see...more than the 5v power and ground.

These capacitors are just connected between the ground and +5v input lines on your rectifier board.

This is the opamps pins if I'm not wrong. Found the pdf for it. Are the numbers pointing out from the opamp on dmitris schematic the corresponding pin on the ompamp like I've highlighted to the left?

Yes.

Regarding the op-amp, I couldn't find one on the website you mentioned (Farnell does have them though), besides, when I made my rectifier circuit Dmitri mentioned that he no longer used the LMC6034 and gave me some alternatives, which they don't list either. I did however find this: http://www.electrokit.com/en/mcp6002i-p.49312, which *might* be suitable, though Dmitri would have to confirm this. The difference with the others is that it is a dual op-amp instead of a quad. I'll explain: when making the circuit for one input (e.g. snare), we only use half of the chip (two of the amps it contains, hence the two "triangles" you see in the schematic). In reality, you don't need two op-amp chips but one (it contains 4 amps), and even then you're only using half of it, unless you want to use it for another input, adding the corresponding components. So, the one in the above link is half the size (2 amps) but would be suitable for one PS input. If it is confirmed to be suitable, you can just go ahead and get that one, if not, I can send you one of mine (mcp604).
I'll have a look at the rest of the stuff you linked to tomorrow.

[rockdude]

I did however find this: http://www.electrokit.com/en/mcp6002i-p.49312, which *might* be suitable, though Dmitri would have to confirm this.

Dmitri said it should work based on the specs, but couldn't tell for sure without testing.

I also asked the staff at electrokit and they took a look at the schematics and gave me this list of components:
C1: 1uF http://www.electrokit.com/yxf-1uf-50v-105c-o5x11.44071
C2: 100nF http://www.electrokit.com/keramisk-100n ... iell.45633
C3: 1nF http://www.electrokit.com/keramisk-1nf- ... 54mm.41768
C4: 1nF http://www.electrokit.com/keramisk-1nf- ... 54mm.41768
R1: 100k http://www.electrokit.com/motstand-meta ... 100k.42542
R2: 15k http://www.electrokit.com/motstand-meta ... -15k.42532
R3: 15k http://www.electrokit.com/motstand-meta ... -15k.42532
R4: 10k http://www.electrokit.com/motstand-meta ... -10k.42530
R5: 12k http://www.electrokit.com/motstand-meta ... -12k.42531
R6: 330 http://www.electrokit.com/motstand-meta ... 330r.42512
D1: 1N4148 http://www.electrokit.com/1n4148.41532
IC Socket http://www.electrokit.com/dilhallare-14pin.41964

They didn't have the opamp as already we know, but offered me this: http://www.electrokit.com/lm324d.46036 (EDIT: this opamp wont work according to dmitri, so that's out of the equation). Dmitri recommended LM6134 or MCP604

[ignotus]

Those components should be fine. As for the opamp, just pm me with your address and when I get a chance I'll pop one in the post for you; the MCP604 has been tried and tested so I suppose it's safer to go with that. The drawing will have to wait a couple of days - I didn't realise today and tomorrow were holidays where I live so I have to take my daughter out to play

[rockdude]

Those components should be fine. As for the opamp, just pm me with your address and when I get a chance I'll pop one in the post for you; the MCP604 has been tried and tested so I suppose it's safer to go with that. The drawing will have to wait a couple of days - I didn't realise today and tomorrow were holidays where I live so I have to take my daughter out to play

Thanks, the list of components the staff presented was ok then?...I guess it was that list you commented on? Just to be sure.
Much appreciated...I'll PM you! I'll patiently wait for the drawing. Tomorrow is holiday here too so I'll have to find something fun to do with my daughter as well

[ignotus]

Yes, that's the list I meant - those will be fine. I can't remember which right now, but there are a couple of capacitors that can be left out. In the original thread with the rectifier circuit (near the end) Dmitri told me which ones they were. Can't search now cause I'm on a small phone...

Have fun with your daughter

[ignotus]

Found some time to do a quick drawing. It's a bit messy but I think it's clear enough:

rectifier drawing.jpg

C3 and C4 can be left out.
Where lines curve when they intersect it means they must not touch each other (assuming they're bare wires). Dots at intersections mean they are soldered there. There are several places on the MD pcb where you can connect +5v and ground. A good place might be the header that used to be there to program the atmega and which is now unused, or you can take it from the hi hat jack... whatever you prefer.
To connect the recitifer board to the snare input, unsolder the wire from the tip of the snare jack. Connect/solder a wire from "to snare pad" to the jack tip. Connect/solder a wire from "to snare input" to the wire you unsoldered earlier from the jack. Connect +5v and ground to wherever you have chosen and you're done. You might want to fix the board to somewhere inside the case.
Oh, and one more thing, get a socket for the op-amp, one of these:

socket.jpg

[rockdude]

Thanks for the drawing!

I guess this socket would be good for the IC? http://www.electrokit.com/dilhallare-14pin.41964
I'll soon order the parts

Still not sure where to connect the power and ground on the megaDRUM-board though. Can you point them out on this picture?

To connect the recitifer board to the snare input, unsolder the wire from the tip of the snare jack. Connect/solder a wire from "to snare pad" to the jack tip. Connect/solder a wire from "to snare input" to the wire you unsoldered earlier from the jack. Connect +5v and ground to wherever you have chosen and you're done.

This part is hard for me since I have stacked jack inputs on my board. Where should I solder and unsolder? See pictures below:

[ignotus]

Yes, that socket is fine.

Still not sure where to connect the power and ground on the megaDRUM-board though. Can you point them out on this picture?

I have a copy of Synthex's "Quick Manual" for the 3.1 board and all the pinouts are explained there: I'd take power and ground from the ICSP Pic connector. Power is pin 2 starting from the top of the header as seen in your picture and ground is pin 3 (the header is the one beside the pic microcontroller labelled "ICSP PIC").

This part is hard for me since I have stacked jack inputs on my board. Where should I solder and unsolder?

Hmm, I hadn't counted on the input jack pcb. Not to worry. Look at the flat ribbon cable plugged into the 24 input connector on the MD board. Starting from the top (as seen in your picture), the snare head wire is the 9th one. Carefully (very carefully!) separate it from the rest and cut it, say, halfway between the MD board and the jacks. Now, the part coming from the jacks goes to "To snare pad" and the other part goes to "To snare input" - you're putting the rectifier circuit "inline" so to speak.

Successful completion of this procedure qualifies you as a certified Megadrum surgeon

[rockdude]

Thanks again for clarifying!

You did mean the ribbon cable for the 32 input connector on the MD board? (not the 24 input connector). I downloaded the quick manual and saw that the 9th one is the snare head on the 32 input connector (pic below)


I opened up my megadrum case and took a picture of my ribbon cable running from the main MD pcb to the 32 input connector on the 32 input pcb (See below). I guess that the red wire is the first? So counting from that the 9th should be the one I've marked with a blue mark (and red cross) in the picture below. That wire I should separate a bit from wire 8 and 10 so that I can cut it and connect the "To snare pad"-wire to the wire part that runs to the jack input on the 32 input connector pcb....and the other part of the wire running to my main MD pcb connects to the "To snare input"-wire? I really want to be a certified Megadrum surgeon!

[ignotus]

Yep sorry, I meant the 32 input connector... As for the exact wire, I can't be sure looking at that photo with the jacks - it's the ninth wire starting at the top if you were to look at the ribbon cable plugged into the MD main board as shown in the photo above. You're correct about how to connect everything once you have the right wire.