Hello Forum,
i am a Guitar player with a common problem. I use a couple of single effects pedals in my Setup. When i have to change my sound during a song i often have to turn multiple effects on/off and switch amp channels. There are commerical solutions to this problems but they are very pricey and often you get much more than you need but lag some functions you need. So in the end to build your perfect setuo you would have to buy multiple very pricey units. I decide to build a switching system myself wich can do exactly what i want and not more.
I researched a lot in the last days and found a lot of good ideas and projects to start from. I will post my whole idea, schematics and code in the future but i am posting because i am very confused right know on how to handle a specific problem:
Just to keep it simple i will explain my problem on an reduced two pedal setup.
I will have a footcontroller with two buttons to select preset a or b. This footswitch will communicate with the rack unit. in the rack unit i have two button on arduino inputs, two led´s and four relays on the outpu side. and a 3rd button for saving presets.
now i want that i can select one of my two presets via the footswitch and then select wich of the 2 effects loops (switched by 2 relays each) is active or not. Save the selcted options to the preset with the button and be able to recall it via the footswitch. The led should always show wich effect is active. so if i switch the preset you should see by the leds wich of the effects loops is active.
The problem now ist that i want to avoid using too many pins on the arduino because in the end its always active when the two correspoding relays are engaged. If i use a common pre build relay card i could drive the relay coils with an external powersupply but even if i do that the current needed is reltivley high. so if i solder the led on the same pin as the output signal for the relay. the output current of the arduino would be to high. The best solution would even be using one output pin to activate both corresponding relays and the led. But this would be way too much curretn for the arduino output especially when i expand the set up to more effect loops. I read a couple of different appoaches to that problem so ia am little confused at the moment.
Is there a simple way to solve my problme. BTW i did a lot of Guitar circuits even some more complicated with sustainers but i never designed a circuit board. so any solution involving pre manufactured circuit boards (I like the idead with the shield and simple arduino hardware options a lot !!!) would be very nice.
Thanks in advance!
Martin
The relay coils are going to require a certain amount of current (depending on the particular relay). Generally, you'll have a transistor or other driver circuit so the current doesn't have to pass-through the Arduino.
So really, the only reason to worry about current would be if it's battery operated and you're worried about battery life.
You may be able to use an analog switch IC which works something like a solid state relay, but it's not isolated and requires less current to switch than a relay. Another option would be a solid state relay which works optically and uses an LED instead of a coil. Just make sure you get a solid state relay rated for low voltage AC signals. (Some solid start relays can only switch higher voltages and some switch DC only.)
i never designed a circuit board. so any solution involving pre manufactured circuit boards
I've built quite a few permanent projects with [u]plug-in breadboards[/u].
Or, you can find relay boards with drivers already on them. You'd just have to make the connections between the Arduino and the relay board and power supply.
I'm not following exactly what kind of switching you're trying to do, but one thing to be careful about is "floating" inputs & outputs where the voltage of an unconnected input or output can "float up" from ground. Then when you make a connection, you get a "click" or "pop".
If you get clicks or pops when switching, add a resistor "permanently" to the suspect input or output. For direct (high impedance) guitar signals use about 1 Megohm. For line-level signals or signals out of an active effects box, use about 10K Ohms.
Hi Doug,
thanks for your reply and for the Tip with the Breadboard. Didn´t came to min using them for a permanent Project but your right. why not?
On your other response: I think you got me wrong. I already planned on using Relay boards with Optocouplers and a own power supply for the coil. What im worried about ist that even the control signal for per relay draws 15-20 mA per channel and the LED woul draw another 13mA. If i now would drive with 1 arduino pin both corresponding relay channel and one LED i end up wit 43-53 mA per Arduino pin. ive read different MAX ratings from the Arduino Mega but i read that it shuoudnt exceed 20mA per pin and 200ma per Pin Group.
Am i doing something wrong in my equation? What i didnt realy get about the relay card is that the Specs show: 70mA coil current, 4mA per control channel and 15-20 mA control current. Dont now wich control current spec is the right now. But even if i take the 4mA i am at 21mA for 1 LED and two Relay channels. Is that to much for the Arduino. I m not shure here and don´t want to destroy the Board or work it at max all the time.
Martin