Author Topic: Some advice with a build  (Read 2728 times)


Some advice with a build
« on: January 12, 2008, 10:01:00 AM »
Hey guys,

I'm a bit of a noob with the electronics side of things - I'm a programmer by trade and I've done a bit of microcontroller programming in the past, and built a few basic bits and pieces (including the beginners tut from this site). I'm thinking about building something custom - a programmable 8 (maybe 10) way foot controller that incorporates a bunch of true bypass loops, an interface for the footswitch input on my ENGL Powerball, and some MIDI outputs. The idea being that I can hit one foot switch and have it change to the lead channel on my amp and kick on my boost pedal and wah pedal, or whatever. I'm intending on using an AVR microcontroller - probably an atmega169 as I already have a dev board for that and it has plenty of I/O pins, an on-chip UART, etc so should be able to do everything I need.

Now, I guess for the true bypass loops I should be using relays to switch them on and off - and from what I've read, the best way to switch relays from a micro would be using transistors or optoisolators on the output pins, right? The amp footswitching stuff I'm thinking I'll rip the board out of my ENGL Z-5 pedal and just use relays to switch the inputs on that. The other alternative is reverse engineering the pinouts on the Z-5, but I think that might be beyond my skills a bit at this point - the Z-5 uses 6 momentary footswitches, has a relatively complex-looking board, and connects to the amp with a serial cable with DB-9 plugs. I've asked ENGL for some help, but haven't heard back from them yet (and not exactly expecting that they'll come through with the goods). If anybody knows how the "custom footswitch" stuff on the ENGLs works I'd be grateful for the info. The MIDI stuff looks pretty easy - it's basically just serial output!

So basically my questions are:
- Relays are the right thing to use right?
- What kind of relays are best for audio applications? Preferably 9V
- Optoisolators or transistors?
- Any suggestions for multi-optoisolator or multi-transistor ICs, or should I just be using individual ones?
- I've had a bit of a google and I think I can figure it out, but can anybody suggest how the circuit would work going from micro output -> relay?
- Oh yeah, can anyone suggest a nice pretty backlit LCD module? 16x2 or 20x2.. I'm considering laying the device out with two rows of footswitches and a row of LCDs in between with the patch names (just for the geek factor - it's much nicer than masking tape and sharpie!)

« Last Edit: January 12, 2008, 10:45:23 AM by snare »


Re: Some advice with a build
« Reply #1 on: January 19, 2008, 06:54:56 PM »
relays: yep, thats the right route

opto .vs. transistors: transistors are cheap and work great for controlling relays. Individual ones work fine.

how to connect hook it up

i've seen schematics for the engl footswitch/amp somewhere, I'll see if I can find it

on the serial connector:
pin 1 = power (+24V apparently)
pin 2 = clean/lead (connect to ground to switch the channel)
pin 3 = ground this to disable the regular footswitches on the 1/4" jacks (ie: give this one priority)
pin 4 = not used
pin 5 = ground
pin 6 = lo/hi gain (same deal a pin 2 on the switching)
pin 7 = not used
pin 8 = style/contour (again, same thing)
pin 9 = master A/B (same thing)

as you can see on the engl schematic, you don't even need to use relays on these, you can do it with transistors.

« Last Edit: January 19, 2008, 07:10:35 PM by Seljer »


Re: Some advice with a build
« Reply #2 on: January 22, 2008, 09:52:21 PM »
CHAMPION! Thanks heaps  :icon_biggrin: