Relay Trigger Type Is Short

Question

I purchased a 12v Timer Relay that has no instructions but after messing around with it I have it somewhat programmed. My issue now is using the trigger inputs, the relay information states that the trigger type is "Short". What does this mean? I am trying to trigger the relay from a TEMT6000 light sensor https://www.sparkfun.com/products/8688, when the light goes off I want the relay to trigger. Right now the only way I can get the relay to trigger is to short the SIG and GND wires at the sensor.

I have figured out most of the timer and how it works. With the light on the voltage out of the sensor is 4.85 and with it off (as best as I can darken the room) 2.15v. However at 2.15v it doesn't trigger the relay, how do I pull the trigger lower?

Answer 1

It could mean:

• "Short-circuit", as in connected to ground as you have found by experimentation. This is not normal terminology though.
• "Short-duration", as in "a brief connection of the trigger to GND will start the timer. Normally a hundredth of a second would be adequate for this so I don't know why they're looking for 1 - 3 s.

You'll have to do more experimentation. I suggest:

• Set up a 10 s delay.
• See what happens with a 0.5 s trigger (to GND).
• See what happens with a 3 s trigger.
• See what happens with a 5 s trigger.
• See what happens if you hold the trigger on indefinitely.

You should be able to figure out from these tests:

• Whether the trigger duration matters.
• Whether the load switches immediately on trigger.
• Does the load switch off when trigger is removed.
• Does the load stay on if the trigger is held or does it switch off until the trigger turns off and on again.

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Voltage does change with the sensor, I have 4.85v with the light on and 2.15v with light off but that doesn't trigger.

The problem is that your sensor is giving an analog output. Your trigger requires a digital signal, on / off.

^{simulate this circuit – Schematic created using CircuitLab}

Figure 1. Potentiometer trigger test. Figure 2. Diode voltage dropper.

It seems as though your sensor output voltage swing is not adequate to trigger. You need to do some experiments:

• If you have a potentiometer you could test to see how low the voltage has to go before the trigger works. Hook it up as shown in Figure 1 and monitor the voltage on the input.
• Then, if you have a few diodes, you could try the circuit in Figure 2. Each diode will subtract 0.6 to 0.7 V from the sensor signal and, hopefully, drop it below the threshold voltage for the trigger. Again use your multimeter to check what's going on.