I'm currently looking into replacing an old domotica board with an Arduino, and would like to design a shield that can be used to switch the already installed impulse relays (in the main fuse box). I was thinking to drive the impulse relays using external current (12V/24V transformator already installed) and NPN transistors. I was wondering if:
- The transistors would suffice to drive these relays (only a short pulse needed to switch)
- I need to add an extra diode to protect the arduino digital outs?
If anyone could just sketch me the components to use between the digital out (after shift register) and the impulse register...
Thanks a lot:-)
I just realized that the coil of the impulse relay is probably driven by AC... I'll need to find out, and use relays instead...
The transistors would suffice to drive these relays
I need to add an extra diode to protect the arduino digital outs?
You need a diode across the relay coil, yes.
just sketch me the components
It's just the same as driving a motor.
Thanks for the reply. I've just checked, and indeed: the impulse relays are driven by 12 V AC (and as far as I remember I can not switch AC using a transistor, can I?). My next alternative would be to use a MOSFET relay to switch the 12V AC using the Arduino 5V to trigger the MOSFET state? Or would you propose another alternative?
My next alternative would be to use a MOSFET relay to switch the 12V AC
No you can't switch AC with a MOSFET (well not single endedley). What you need is a device called a triac. Get one with an optically isolated gate or drive it from an opto isolator as you can't have a common ground with an AC signal. (well not single endedley).