First Project: MIDI Guitar Amp Channel Relay Box - 74HC595 + ULN2803 + 8 Relays

I posted this in the "Motors, Mechanics, and Power" forum but I think it probably fits better here:

This might be a bit ambitious for a first post/first project but here goes... I have multiple guitar amps and a nice MIDI controller (Voodoo Labs Ground Control Pro) and while my GCX looper can control channel/options switching via MIDI, I have to use and entire loop on the GCX for each option which isn't great considering my Mesa Studio Preamp can use 3 alone (channel, EQ, Reverb). So, I thought it would be cool do make a device that does this on it's own. The actual channel/option switch is extremely easy since it just closes or opens a circuit via 1/4" mono jack by connecting or disconnecting the tip from sleeve. My first test can be seen here: http://youtu.be/n7NPA-GzxU4. I used a simple relay schematic from makezine (linked in video comment) and changed the Arduino "blink" code to switch the relay on/off every 3 seconds.

Now, here's the issue... while I feel perfectly comfortable soldering components due to working on guitars (pickup swaps, control changes, etc) my electronics knowledge is EXTREMELY limited. In the last few weeks of tinkering with this design I have learned a TON but still fall short of completely understanding the portion from the 74HC595 on (electrically that is, conceptually I think I've about got it). I keep thinking that I'm missing something... Anyway, I have attached the schematic that I have so far. The funny thing is that I'm unsure of how the LEDs are placed of all things. I find it slightly amusing that I got this far and am tripped up on where and how to put the LEDs in place. But, I placed the LEDs in the only way that made sense to me. Would this work? I haven't decided what LEDs I'm using yet so I put 220 Ohm resistors in for now but will calculate the correct value before building it. Does going through the Darlington Array affect how they're wired up though?

Also, for this type of project, did I choose the right type of relay? I still don't completely understand how solid-state relays work and if they would work in this scenario although I'm leaning towards "no".

One last disclaimer: Everything I've learned about electronics has been what I have read on the internet over the past few weeks. That being said, if there is some HUGE glaring mistake... my bad.

Hopefully the schematic is readable, I'm new to that as well ;)

did you draw the schematic up or did someone else?

i am not working on the relay side of things just yet, more interested in the foot controller sending the serial midi protocol. I have the behringer fcb1010 foot controller and i think its pants. Doesnt seem to work the way i want/thought it would with the ada or through cubase.

surely you need transistors on the 8 outputs of DT1 to switch in the relays so more juice is provided for leds and coils?

kh602: did you draw the schematic up or did someone else?

I did everything myself except for the MIDI IN/MIDI THRU which reminds me that I have to find that link again to credit it...

kh602: i am not working on the relay side of things just yet, more interested in the foot controller sending the serial midi protocol. I have the behringer fcb1010 foot controller and i think its pants. Doesnt seem to work the way i want/thought it would with the ada or through cubase.

When I was researching this, I found a TON of projects that send MIDI data from the Arduino so you should be able to get a lot of examples. Where I had trouble was decoding MIDI data but I think I've got that solved, unfortunately I can't test and finish my code until the hardware is done though ;). I'll reply to your thread with my thoughts on this.

kh602: surely you need transistors on the 8 outputs of DT1 to switch in the relays so more juice is provided for leds and coils?

If I understand it correctly, the way the Darlington Array (ULN2803) works is that it controls the connection to ground hence the 5V rail being connected directly to the relays AND to pin 10.

I just realised something though, since I have everything connected to the same 5V rail, my resistance might be off everywhere. I might need to rethink my power situation. Also, I left off a ground symbol that should be connected to the GND pin (8) on the ATmega328, I'll fix it later.

cool, what material did you find about sending program changes etc.? i have looked but having difficulty getting parts to work.

sites i have come across

http://hyperglitch.com/articles/standalone-midi-controller http://interactive21.net/wordpress/archives/9 http://arduino.cc/playground/Learning/MidiFoot http://www.codeproject.com/Articles/38203/Arduino-Based-MIDI-Expression-Pedal

and theres a few others i have seen, i imagine you have seen these same links?

cheers

Hello!

How can you write your settings in the internal eeprom?

Regards