over-sensitive solid state relay

Forum 2005-2010 (read only) Hardware Interfacing
1

I have a solid state relay hooked up to the ardunio via a 1K resistor to a 2n2222 transistor. I'm having problems with it being over sensitive. It will even turn on with when my finger touches the wire connecting to the base of the transistor. Can I run it directly from the ardunio without the transistor? I've had it with a pulldown as well and it doesn't help much.

thanks

2

How do you have it hooked up? Which relay is it (datasheet)?

If you can turn it on by touching the base terminal it suggests a wiring error (or loose wire...)

--
The Quick Shield: breakout all 28 pins to quick-connect terminals

3

Did you forget to use pinMode() to set the pin as an output?

Since an SSR doesn't take much current, turning on the 10K pullup on an input pin would probably provide enough base current to turn on the SSR.

Turnong off the pullup would leave the base of the 2N2222 floating, giving you the "touch switch" effect.

4

Most solid state relays don't require any extra components between the digital pin and the SSR itself. The low voltage end is an IR LED usually with its own current limiting resistor. Most of them have a wide operating voltage and 5V is usually towards the lower end of the range and they draw only a few milliamps at that voltage. Taking the transistor out of the equation would remove the finger switch effect.

Before the days of DMMs I'd test transistors with a analogue meter on resistance setting and using my finger on the base to make the circuit.

5

I've driven them from an ARM (3.3V output) without any problems. It depends on the relay, of course.

6

I've had it with a pulldown as well and it doesn't help much.

What value of pull down and where did you put it?

Can I run it directly from the ardunio without the transistor?

Yes although check the data sheet to see if you need a series resistor 90% of SSRs don't.

7

thanks,

I'll double check the datasheet which I'm sure I can find online.

The pinmode is set to OUTPUT and there is a pulldown resistor I had dropped down to 4.7K from 10K which I believe should get rid of any floating voltage.

I'll try it without the transistor. It only requires 3-24vdc to switch and likely not too much current.(?)

8

not too much current.(?)

No, it is always 5 to 30mA... When they say "3 to 30 volts" or such then there is a current limiting device (resistor or more complex things) already in it..