I am using this SSR connected to an Arduino.

I am running a very simple code similar to this one: (like the Blink example)

   digitalWrite(1, HIGH);
   digitalWrite(1, LOW);

When I start with the Arduino pin LOW the SSR is off. But after setting the Arduino pin to high my problem is: the SSR stays always on. Even if I set the Arduino pin to LOW the SSR won't stop letting the current pass through. What do I have to do set the SSR to off again? (Or do you even think the SSR is broken?)

Schematic http://solutionit.ch/schematic.png

  • 1
    \$\begingroup\$ Can you show us the schematic of how you wired up the SSR? \$\endgroup\$ – stevenvh Aug 18 '12 at 16:57
  • \$\begingroup\$ i can't do any better at the moment (see image link in post). does this immage suffice? :) \$\endgroup\$ – ndrizza Aug 18 '12 at 17:27
  • \$\begingroup\$ What are the resistor values? \$\endgroup\$ – stevenvh Aug 18 '12 at 17:30
  • \$\begingroup\$ left: 100 ohm, right: 270 ohm \$\endgroup\$ – ndrizza Aug 18 '12 at 17:35
  • \$\begingroup\$ The 270 \$\Omega\$ gives you 14 mA, which is a good value. The 100 \$\Omega\$ gives the LED 30 mA, which might have been too low to keep the triac on, but on your SSR it apparently still works at 30 mA. \$\endgroup\$ – stevenvh Aug 18 '12 at 17:39

The SSR has a triac as switching element. A triac needs a pulse on its gate to go on, but after it goes on it will stay on until the load's current drops below a hold current. This makes that a triac isn't suited for switching DC, only AC, because there the current will drop below the hold current twice per mains cycle.

So don't use it to switch the LED, that's DC. Besides, you don't need a relay at all (not even a mechanical one) to switch a LED on and off. For that we usually would use a transistor.

  • \$\begingroup\$ thanks! yes i'm switching a lower DC current for test purposes before going to high current. thanks so i'll try the higher current (AC) directly. i'm a bit afraid tough.:) \$\endgroup\$ – ndrizza Aug 18 '12 at 17:34
  • \$\begingroup\$ @ndrizza - Your relay drive current is good, so if you don't overload it (that's at current higher than 8 A) you should be OK. Success! \$\endgroup\$ – stevenvh Aug 18 '12 at 17:41

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