I am attepmting to activate a 12v relays coil with 2.74v. The 2.74v comes from an light sensor, so my goal is in daylight the relay is on and at night it is off. Is there anyway to boost the power from 2.74 to enought to turn on the relay? Or anyway to change the activation level of the relay?
thanks,
Josh
Find a relay with a 2/3 volt coil Google Omron or wait for Oldspark or Dualsport to see this and give you a circuit!
-------------
Amateurs assume, don't test and have problems; pros test first. I am not a free install service.
Read the installation manual, do a search here or online for your vehicle wiring before posting.
I'm assuming the light sensors output is based on how much light is present? If so, you'll need a comparator circuit to allow the light to only turn on when the voltage is above your desired set point.
Check out this thread for a diagram on something that may work:
https://www.the12volt.com/installbay/forum_posts.asp?tid=105885&KW
Replace R1 with a 22ohm 1/4 watt resistor and replace D1 with your relay coil (and a diode across it).
-------------
Kevin Pierson
It is an ambient light sensor in the dash of my vehicle. In the sun light the return side of the sensor reads at 2.74v and in the dark the sensor reads .9v on the return side. I added a circuit to the vehicles wiring that I would like to regulated with a relay and the sensor, by getting the relay to close when the sensor is more positive and open when it is less positive. I'll look at that diagram and see if it'll work for my application. Thank you!
POST EDIT: Reply below was before your last.
Disregard it. You will have to use a comparator type circuit as suggested, else something that does not load the existing circit.
/end PE.
There are various circuit for "light sensors" that use the LDR as a voltage divider to switch on a transistor (often to ground the relay).
Other sensors types have similar circuits.
It's usually a transistor and a few resistors and probably a capacitor to avoid short changes. No need for chips etc.
Sorry Kevin I should have mentioned your name as well.
-------------
Amateurs assume, don't test and have problems; pros test first. I am not a free install service.
Read the installation manual, do a search here or online for your vehicle wiring before posting.
2.9V is approaching the turn on voltage requirements of a MOSFET, so that would be something to try, if it's not too critical as far as the light level that turns it on and off. Because it operates on voltage and doesn't load your sensor circuit, it might do what you need.
Three pins on the transistor; Gate, Source, and Drain. The sensor output would just be connected to the gate of the transistor, the source pin connected to ground, and the drain pin used to ground switch your relay. When the voltage across the Gate and Source goes above the threshold, it basically connects the Drain to the Source pin. If you wire your relay to switch on when the driver is grounded, it should click on the relay when the sensor voltage gets high enough.
You might experiment with it to see if the switching characteristics are acceptable as it goes from dark to light.
Ideally the comparator would be the best as far as being able to tweak it to the exact turn on and off, with the ability to put it together with hysteresis, so it won't switch on and off rapidly when the level is right at the switching threshold. For instance, if the light levels go from 0 to 100, it'll turn on and stay on when the light goes higher than 75, and won't turn back off unless the level drops below 25. Without hysteresis, if your threshold is set at 50, once the light level gets near there, the relay might start buzzing just from noise as the level goes above and below 50.
I'd try the crude MOSFET switch first just to see if it'll do, and go with the comparator circuit if it doesn't.
Datasheet for a basic BS170 MOSFET: https://www.fairchildsemi.com/ds/BS%2FBS170.pdf