AVR Synth Part 1

I decided to make JAREK ZIEMBICKI's AVRSYN. But there were only the schematics and no board layout so I had to make my own. So I started laying it out on eagle but I got on a deadlock due to the fact that I didn't want to make a double sided board. I would etch it myself and double sided boards are a BIG pain in the but (vias and such, alignment etc). So I made it on a perfboard. But before that, I decided that it should be made into discrete modules. One for the microchip, one for the D2A (an R2R resistor ladder type) , one for the midi interface, one for the power supply and one for the switch multiplexer.

Here is the main part. I put pin headers to wherever it would connect to another module and got myself a lot of ribbon cable. The AVR is a really simple design. Only the layout makes it complicated. It can be made by anyone (Even I made one!!!).

Posted by Picasa


MRE said...

your solder work looks nice.

might I make a sugestion though?
One way I found to make long rows (3 pins or more) of continuous connection (such as power and ground pins on pinheaders) is the following:
Strip a long piece of wire. I usually cut up cat5 for all of my protoboard work, since it is cheap, thin (two or three easilly fit into one hole for making jump points of multiple connections), solid core, and for bus work it gives me 8 colors...
anyway, with a long piece of solid core stripped wire, tack one end down to one of the pins on the end. Now, zigzag it around all the other pins in the row, like driving around cones in an obstical course.
Finally, tack each pin to the wire and pad.
The reason for this is that if/when you have to make a change, it is much easier to cut the wire and move it. If you have to make a change on an all solder connection, you might overheat and loose a lot of 'back solder' from where you are working. For example, you wouldnt want to undo the whole row, but the row is connected to the wrong thing. Undoing this connection on an all solder joint might result in a cold solder joint later, or 'rip up' several pins close to the repair point. With the wire method, simply cut it at the repair point, make the repair, then bridge the repair point to the row with a small wire.

My method certainly doesnt look as pretty as yours, but it is electrically sound, and uses less solder. I generally find it easer.. but everyone has their preferences on protoboard.

(I hear some people still like to wire-wrap!!! crazy!! ;)

Aris said...

I'm open to suggestions.. I don't have much experience with this stuff so anything is worth considering. I'm gonna try it as it seems quite easier than having to melt tons of solder. To make it this way (my way :) I had to start connecting the holes in pairs and then gather a gob of solder on the iron and connect the pairs and so on. It takes ages to cool down and the components get too hot. I thought I should try using strip boards or some gadgets that apply insulated wire (verowire or something like that) but I will try your way first. Seems quite easy both on execution and on wallet. Thank god I have kilometers of cat5 in my job! :)

Thank you very much!

Aris said...

PS. couldn't care less if it is pretty or not.. :)

Aris said...

There is also a wire known as mod-wire (I believe it is AWG 30). Have you ever tried using it? because cat5 insulation tends to melt away when you solder.

Collin Mel said...

Nice work. How far did you get with the eagle layout? I'm guessing using multiple jumper wires topside wasn't enough?

Aris said...

It could be done I think but because the multiplexer's pins were in the reverse order from the chip's outputs I would have to make at least 16 + 2 jump wires on top.

I will try it today I think and post the board on the file repository.

You are most welcome to make any changes you may like..

(by repository, I mean http://sites.google.com/site/diysynth/)

Collin Mel said...

wait, could this be solved by editing the part layout in eagle?

Aris said...

Hmm I don't think so. If you put the chips side by side you still have a problem :) Maybe editing the code to output the bits in the reverse order.. But hey, I'm gonna give it a shot with lots of jump wires :)

Aris said...

Okay, just remember that my PCB design skills SUCK BIG TIME!

In http://rapidshare.com/users/O5MTP0 there is a file called CPU.zip. It is a first version of the avrsynth (16/32) with lots of jumper wires (seen as TOP side wires (the red ones)). Collin, take a look if you like, I will etch it tomorrow. (And will post some photos too :)

Aris said...

Oh, and by the way, I forgot to put MIDI out.. (Will-do-tomorrow.....zzzZZZZ)

Collin Mel said...

def does not "suck big time"! looks good - def usable as is.

yeah these repetitious connections are a freakin pain to lay out.

Hmmms, i may try breaking up the 40-pin header into 4 10-pin chunks. that might help avoid some of those jumpers - of course I'll have to seee what it does first ;)

Aris said...

The 40pin header is the place where the switches are mounted.. (Sorry, didn't write any comments :(

it is like having a switch between each of the 20 couples of pins.

So, you can divide it as much as you want (horizontally). A bit later I will upload a new PCB with the 6n138 as the optocoupler (this is what I have handy and it is sunday), and the missing midi out.

You can always mail me at akorbeti [at] gmail [dot] com

Aris said...


New pcb, has 6N138 for midi in, midi out and a bit of a jumper cut down..