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Topic: Solid State Relay + Arduino Help! (Read 3368 times) previous topic - next topic


The goal: Turn 60W light bulb on/off with the arduino using a 2N2222a transistor and solid state relay (D2425, 3-23V input, 25A, ~240V).

The setup: My circuit is done similar to this (as posted by someone else), with the exception of the digital pin connected to a transistor to the arduino: http://img687.imageshack.us/img687/2164/arduinossr.jpg

The problem: The light just stays on and does not turn off. While the signal pin does fluctuate between 4.6 to 4.9 repeatedly as it should on the relay, how do I get the signal to drop to 0 and back to 4.9, so as to turn on/off? What pieces of the circuit are missing?

I've read that a transistor wouldn't be necessary to turn on/off a solid state relay since the ssr reads like an LED to the arduino, but this didn't quite work for me, hence the transistor in the circuit.


May 04, 2010, 12:59 am Last Edit: May 04, 2010, 01:00 am by pwillard Reason: 1
Are you sure you need to use a transistor?

Most SSR need very little current so you can drive right from a pin.

Can you show us the SSR being used?


do you have the right kind of transistor? can you post a diagram of your current circuit.


May 04, 2010, 11:43 pm Last Edit: May 04, 2010, 11:44 pm by linux_user Reason: 1
Got it to work without the transistor. There was a simple error in the arduino code.

The D2425 Crydom solid state relay works when directly placed into the arduino's digital pin. This appears to be the cleanest solution for the project (without having to use a mechanical relay and  accompanying external transistor circuit with protection diode).

Thanks for jumping in to help out.


How fast are you switching this on and off? The SSR won't draw more than about 20mA so you really don't need the transistor.


So far the relay has been tested to turn on/off the light every 3 seconds.  Ultimately, the relay (in addition to 2 others)  will be used to control 3 lights, where each light is to be switched on one at a time as a certain threshold is met. The entire project is a combination of arduino, processing, mysql database, and php to remotely control certain features of the software.

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