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.

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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?

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    \$\begingroup\$ Welcome to SE. Please at least give us a photo and a part number. Also add a link to the light sensor so that all of us don't have to look it up. Put the information into your question rather than in comments. \$\endgroup\$ – Transistor Feb 7 '16 at 14:24
  • \$\begingroup\$ Sensor sparkfun.com/products/8688 \$\endgroup\$ – BS1963 Feb 7 '16 at 17:33
  • \$\begingroup\$ Thanks. Put the information in your question rather than in comments. This way others will see it as they try to answer the question. \$\endgroup\$ – Transistor Feb 7 '16 at 17:36
  • \$\begingroup\$ If you know how to trigger the unit, what is your question? \$\endgroup\$ – WhatRoughBeast Feb 7 '16 at 22:46

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.

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.
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  • \$\begingroup\$ It was what you call a short-duration, I briefly touched the SIG wire of the sensor to the GND of the sensor. So I set the relay timer to have a 10 second delay, at power the timer shows 4 zeros, a short-duration touch and a 10 second delay and the relay powers the load. I didn't notice a difference in the trigger duration once touched it triggered. The load does not immediately come on, again a 10 second delay. The load does not switch off if the trigger is removed. The load stays on if the trigger is held in place but the timer will only pause the count down 10-12 seconds then it starts. \$\endgroup\$ – BS1963 Feb 7 '16 at 22:21
  • \$\begingroup\$ Once running I can at any time in the count down either load on or off I can "short-duration" and the load doesn't change but the timer will pause the count down but again only for 10-12 seconds then it will resume. Nothing seems to trigger it again off or on. \$\endgroup\$ – BS1963 Feb 7 '16 at 22:29
  • \$\begingroup\$ 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. \$\endgroup\$ – BS1963 Feb 7 '16 at 22:32
  • \$\begingroup\$ I think you're getting the hang of the operation of the timer by the sound of things. Regarding the sensor, you'll need to feed the sensor output into a threshold comparitor and set the threshold voltage midway between your two readings. Feed the output of the comparitor into your trigger input. \$\endgroup\$ – Transistor Feb 8 '16 at 0:08
  • \$\begingroup\$ Well I have to go find out what a threshold comparitor is and get one ordered! Thank you for the help! \$\endgroup\$ – BS1963 Feb 8 '16 at 0:21

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