Interfacing Velleman Kit K8056

I would like to drive the inputs of the Velleman relay board (K8056). The schema of the card is available here:

Do I have to use a DS2405 (and a 2N3904), or can I directly use the digital entry of the Arduino (i would bet on the 1st proposal)

If someone can help me with the wiring, that would be great! :wink:

ps: using this relay card, do you think I can drive small water pump (for a fish tank)?
ps: I will use it on a 220V power source.... ::slight_smile:


  1. Yes, you can use the Arduino's digital outputs to control it; based on the schematic, using terminals OUT1-OUT8 (which connect to NPN driver transistors). I would personally throw a buffer IC in between, but then again I am paranoid.

  2. Also - you can control it via RS-232; so in theory you could set up a MAX232 device on a couple of I/O pins and go that route.

  3. Yes, these relays should be able to control a small pump; their contact current rating of 5A/230VAC is more than plenty, I would think.

  4. Finally, you are spending waaay too much money for something like that; in another thread I noted how you could build a similar relay-controller for well under $50.00 (with 20 outputs - you could probably do 8 for under $25.00). If you went with using opto-isolators driving high current triacs, you could probably do it for under $10.00 (provided you were only driving AC loads, of course).

Spend your money how you like though; I just know that Velleman kits, while nice, are pretty pricey for what you get (and what you could build yourself).

(i would bet on the 1st proposal)

You would lose :sunglasses:

There should be no problem at all with driving those transistors directly from Arduino pins.

If you want to save I/O pins, you could use a shift register or port expander, but you don't need to.

Thanks for the answer. I still have a question. What is a "buffer IC". I am not sure of what it means.

OK, my project is progressing well and I am able to use the shift register to put LEDs ON/OFF to simulate the relay cards I am waiting for.
I finally changed my mind and went for the Futurelec relay boards (4 i/o AC and 4 i/o DC), so 8 i/o total, that I can manage with my shift-register (DC Opto-Isolated Output Board and 4 Channel Opto-Isolated Relay Board) :sunglasses:

What kind of electronic components should I put to act as a buffer IC between my shift-register pins and the screws of my relay boards ? Is a 2n2222A a good choice ( :-?

I still have a question. What is a "buffer IC". I am not sure of what it means.

The simple answer is it is simply an IC that sits between a set of digital inputs and outputs and acts as a current booster and protective layer between those - so if something goes wrong, the buffer gets fried.

In a way (and probably how they are implemented, but I am not sure) they are simply driver transistors packaged in an IC (think of it like a darlington driver IC, but without the secondary transistors).

The classic version is the 7404 hex inverter IC; the only problem with it is that it inverts the signal (basically acting as a NOT gate). There are versions which don't do this as well.

It probably doesn't matter nowadays with microcontrollers being so cheap, but I come from a period where an 8-bit CPU ran $20-50.00 in low quantities and you didn't want to blow them by hanging just any old transistor off your data bus.

Those were the days when you could look at your i/o port wrong and it would blow...


So something like the M74HC367
If yes, can you confirm i can use it for only 6 of my 8 shift register outputs?, so I will have to buy 2 of them?

Yes - that should work OK; and yes, you would have to buy two (might as well buy a tube worth if you can afford it, you'll probably need some more in the future if this isn't going to be your only project).

Also - remember to tie G1 and G2 to ground (so the signals will pass thru to the outputs - read the datasheet) - you could also control G1 and G2 with the Arduino (if you needed that capability for some reason).


Thanks again. Since you are reading in my mind, do you know by which way I could use only 1 arduino pin to control both the shift-out register OE pin and the G1 and G2 pins of the IC buffer at init time. Since OE must be low and the other be HIGH before using them, I do not see any easy solution, do you?


up? nobody?