Interface w/ EFX-TEK (Parallax) RC-4?

Ok, so I'm very new to all of this so please excuse what may be a silly noob question, but before I purchase an Arduino and start playing around - I'm wondering how hard it would be to interface with the "RC-4" from EFX-TEK:

I ask because I'm not sure how to build something like the RC-4 (is it easy?), and it seems simple enough to interface with one of the Parallax Basic Stamps which I was thinking of purchasing prior to finding the Arduino.

I did a lot of "googling" and searching and could not find anyone already doing this - so any help or suggestions would be great. One of the main reasons I'm looking at the RC-4 is because you can chain up to 4 together and control them all with just I/O – and for my application I need a lot of power control.

Thanks, Josh

That looks like it will work, but I am not sure about the 'chaining' ability.

Anyway-- it is bit of a waste of money.

Three of their serially addressable boards will give you 12 relays, for $90USD plus relays.

For about $5 plus relays, you can mount your own relays on perfboard and be done in under an hour.

If you want to control 12 of the Crydom relays they use, just connect each relay's input to an Arduino Digital out pin through a 470R resistor, and connect each relay's ground input to the Arduino's ground. Program the Arduino as you want to turn on the relays. That is all you need.

Hope this helps



Yes, that is helpful, and I totally agree about the waste of money (it gets up there for sure). I would love to not need to use something similar, but I need all 16 relays where as as you described I could get 12 with Arduino by using every single digital pin. I did not mention earlier, but I also need 2 pins for a planned serial LCD and 2 more for a keypad (or maybe not depending on how I use the keypad). This would limit me to even less relays.

Perhaps my question should be - How did they do this serialy addressible board, and could I do it with Arduino? - So I can make my own.

  • OR -

How can I address 16 relays and still leave room for 2 other serial devices?

After looking around some - I think I want an I2C setup:

I have more reading to do there, and may find my own answer, but can anyone point me to an example for this on anArduino?

Thanks so much for the help and the quick reply!

-- Josh


making a whole new board that talks to the serial port is a pretty complicated process...

Instead you could just 'expand' one or more of the pins: - try the LEd tutorial here, which can be chained to drive numerous leds (in your case you can just replace the LED with the Crydom relay) - Something similar can be achieved with a 74154 address decoder

Hope this helps


Thanks for all the help, I was able to find lots of options including the one you provided which sent me in the right direction. I think I can really lower my costs - and later might consider something like this for an I2C I/O expander:

Now I'm just trying to find a relay that is cheaper then what I have found so far. $10 per relay, needing 16 relays.... thats a lot more then I wanted to spend.

Where do you all shop for parts?

Thanks again, Josh

hey Josh

that looks like a good option.. the 74154 does the same thing but it is $2 and takes four input lines to give you 16 pins.

Getting parts the cheapest way depends on where you're located... YEs those relays are very expensive, but you could try a photocopy repair place, as they always have old scrap machines with them inside... otherwise some place like the electronic goldmine or Jameco should have a decent price. There is also a list of electronics stores in the 'Playground' Wiki.