Hi, I am looking for basic gudie(s) to set up a macbook w/ pd, an arduino uno, and a board with 8 relays.

The ones I find are very old, from 2011, and I do not want to make any mistakes so to damage the boards.

Thankful for help.

It's nothing specific that I do not trust, just in general it can be a sign that somethings is abandoned if it is not recently updated. Updating firmware when you are not sure what you are doing can be bad, for one thing.

Aside from pd and arduino, connecting the relays to the arduino feels a bit scary in terms of power handling. The relays seem to want more power than the arduino can supply. Then I got the impression that you can not just connect any old power supply else it might fry.

:/

@cfry I bought (something like) this for my RPI....... https://solarbotics.com/product/52270/
There is a 5V supply required (a USB power supply will do it), and there is an opto isolated dc driver for every input.
Basically the Arduino, RPI, whatever, is just lighting up an encapsulated IR LED (5V 5mA)..... so no electrical contact is made.
The relays are activated when the inputs are pulled down to 0V........ but it looks like this one can work the other way as well (jumper selectable).
I remember paying about €8 for mine.
David.

Thanks.

I got this one: https://goo.gl/images/KZJsUy

I think I will try to find a power supply of maybe 12v and connect it to the arduino, and then give the relay power from the arduino board pins.

@cfry I think it would be much better to use an old USB power supply (phone charger / other?) to supply the 5V power to the relay board. Taking 5V from the Arduino for that will stress the 5V regulator of the Arduino, and could cause some instability as the relay coils are powered up.
David.

Ok, I might do it like that, use a USB charger. Using multiple power sources can introduce problems sometimes though. But as of now this might work.
I was looking at this guide: https://www.open-electronics.org/the-power-of-arduino-this-unknown/

I got the impression that the arduino will forward the external power through the Vin pin.

@cfry On the RPI there are the gpio pins and 0V and 5V and I think 3.3V. The 5V can supply some power, but it is limited and best used for reference. Connect your arduino to the inputs and 0V (Gnd) and 5V (grouped together on the relay board), and a separate supply to the 0V (Gnd) and 5V marked on your photo as the power supply for the actual relays.
Better safe than sorry..... as per your OP.
David.

What does Arduino's power supply have to do with the current the relay will let through or not? A relay is an electronic switch which receives power (usually of high voltage) and has three more pins, one for 5V, one for ground, and one to control the actual switch. These three pins are the ones you connect to the Arduino, and Arduino's 5V pin is more than enough to power the digital part of the relay. The high voltage the relay will let through or not has nothing to do with Arduino's power supply and digital control.

Don't know what you're trying to do, and can't really understand the conversation, but thought I post these couple of things I know about relays.

@alexandros hey thanks for getting back.

The eight relay board that I got supposedly requires more power than the arduino can reliable supply, I guess this is due to them being mechanical. It is solved, I cut up a USB cable today and it works fine with the arduino. Flashing and switching.

Next step is to hook it up with Pd, I will try tomorrow to follow the tutorials I have found.

Just want to let you know that it worked fine, all there was to do was to load the firmata code from the arduino menu and launch the pd patch from purr data. I used the "firmata basic" I think. Thanks for you help.