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Topic: Need a basic component to open/close 12v, controlled by a 3.3v signal (Read 1 time) previous topic - next topic

abreis

Hey everyone, help me find a basic component!

I have a 12v remote (it's a garage opener) with a simple push button. I want to take that button out, and put something that can be controlled by a 3.3v Arduino (power sources are separate).

Something simple: Arduino sends a '0', circuit opens, '1', circuit closes.
I wanted a cheap component, but all I can find are $5+ relays that are way overkill for this.

What would you use?
Note: separate grounds, these are two independent circuits.

retrolefty

Quote
What would you use?
Note: separate grounds, these are two independent circuits.


What I would use is a simple inexpensive 5vdc reed relay. It only requires around 10ma of coil current so can be directly wired to a arduino output pin. If used one should also wire a diode across the coil terminals with the cathode lead wired towards the output pin terminal.

http://www.allelectronics.com/make-a-store/item/RLY-541/5-VDC-SPST-N.O.-DIP-REED-RELAY/1.html

dc42

An opto isolator may also be suitable. You'd need to measure the voltage across the push button when it is open and current flow through it when closed to see if this is a viable solution.
Formal verification of safety-critical software, software development, and electronic design and prototyping. See http://www.eschertech.com. Please do not ask for unpaid help via PM, use the forum.

abreis

Thanks for the tips. I'm running the atmega328 standalone on 3.3v and couldn't find a reed switch triggered by that voltage, so I'm going to try the optocoupler.

One concern with the optoc is the voltage drop it causes. I replaced the pushbutton with progressively higher resistors, and found that the garage opener was okay with drops of up to 1.6v. Picked an optoc with a forward drop of 1.2v.

Cheers

DVDdoug

If you are replacing a switch, a relay is the "safest" unless you completely understand what the switch is doing in the circuit/schematic (i.e pulling a voltage up or down, or part of a matrix, etc.)

Is there any reason you can't connect the grounds?  Usually, you can.   Isolation requires either an optoisolator or relay.  (Transformers can isolate AC, but not DC.)

If you can connect the grounds, a xx2003 chip is less than $1 USD (assuming you don't have to pay shipping).   This chip can boost the signal and/or drive a 5V or 12V relay (up to 7 relays) if supplied with the appropriate voltage.  And, it can be driven by an optoisolator if needed.   Be aware that the 2003 is an inverter...  A high on the input "pulls-down" the output.    (If wired correctly, pulling-down the output can turn-on the relay.)



abreis

I wasn't quite sure of what the button did at first, so I thought it'd be best to keep the Arduino separate from the garage opener remote.

Turns out, all the button does is connect the circuit to ground ( battery -- ). I'm actually curious as to why they place the switch between the radio electronics and ground, instead of between Vdd and the electronics. Doesn't matter since this is DC?

I might try to run everything off the 12v battery, with a voltage regulator for the Arduino. That way I'd get common ground and could use a MOSFET as a switch?

Thanks for the tips!

jwatte

You can tie the ground of the 12V to the ground of the Arduino. Then you can drive a MOSFET (like the BS170, at 29 cents a pop) to open/close the 12V circuit. You'll also want a resistor from pinout to gate, and another resistor from gate to ground (to make sure it turns off under all circumstances). At 5 cents each, you're still looking at a BOM under half a dollar :-)

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