Is there a way to hook up the light sensor to the headlights?

[SSMV6]

I got a 2005 EX-V6 sedan and they come with a light sensor in the middle of the dash that's linked to the HVAC system... I was wondering if anyone know if it is possible to rewire the car so that the light sensor can control the headlights, too? I understand that it needs to be done with a couple relays and diodes, and I'm pretty good with electronics, but I don't know where to start. Does the light sensor output a variable voltage depending on the amount of light that it receives or is it like an on off switch (high/low voltage)? Thanks.

[princess]

Here are the directions for testing it..... apparently it's like a regular photo cell......


Remove the sunlight sensor, and reconnect the connector.

Turn the ignition switch ON (II). Measure the voltage between the terminals with the (+) probe on the No. 1 terminal and the (-) probe on the No. 2 terminal with the 2P connector connected. The voltage readings will not change under the light of a flashlight or a fluorescent lamp. Voltage should be:

3.6-3.7 V or more with the sensor out of direct sunlight.

3.3-3.5 V or less with the sensor in direct sunlight.

[princess]

here's the terminal

[SSMV6]

Thank you princess! Any idea where the wire for the light sensor goes to under the dash? I haven't taken my dash apart yet, so I don't know if I can access it near the radio/HVAC controls or if I would have to run a wire to the sensor near the windshield. Thank you. :thumbsup:

[princess]

This might help

[SSMV6]

Those diagrams help a lot. It looks like the output from the light sensor goes straight to the HVAC system. Now if only I know how to wire a relay to detect a change in voltage (versus on/off) then I'd be all set! :thmsup:

[EXLNavi]

Those diagrams help a lot. It looks like the output from the light sensor goes straight to the HVAC system. Now if only I know how to wire a relay to detect a change in voltage (versus on/off) then I'd be all set! :thmsup:


There are a couple of ways to do that.

Cheap, but prone to falsing - use a transistor. Depending on the cell you may have to use a pair of them so that when one is biased it will turn off the other (by shorting base and collector leads). Make sure you have a resistor of high enough value going to the base from the photocell (a few kilo ohms should do going to the base so that the HVAC is not effected.) You will also need to use a damper diode across the relay so that the kick back voltage doesn't fry the transistor. If you want later I can put together a diagram.

Sophisticated - use a PIC microcontroller. This one is a great idea since it's a microprocessor, and you can eliminate falses (such as driving under trees etc) and you can customize it a LOT. It's not that hard but you have to program it in assembly (not very hard, it only SOUNDS hard). I prefer this route.

[SSMV6]

Haha! :lmao: Assembly code! I haven't touched that stuff since I was in college. Never saw any use for it. :banana:

Hmm. False positives was another thing I had to worry about. I didn't want to have the headlights flash every time I pass a shadow! The transistor approach sounds like it's simpler, but the headlights will probably burn out from the constant "flashing".

This is beginning to sound more complicated to mod than I thought! I was hoping that I could build it out of the spare relays I got lying around, but that's probably not going to happen. At first, I thought the light sensor acts like an on-off switch. If it did, then it would've been much easier to do. All I would've needed was one relay and a ground point for the headlight wire. Now, it's beginning to sound like it's going to take up so much of my time to get it working that I wouldn't mind flipping the headlight switch on and off whenever I need it. :scratch:

[EXLNavi]

Most light sensors I've seen are resistors that change resistance with the light, and they are usually made of cadmium sulfide. Others are selenium or even silicon solar cells, which output a varying voltage with the light.

The transistor could be doable if you use a capacitor to delay the turning on and turning off of the lights, but it is crude at best.

The PIC is definitely the way to go, but yeah it's not as simple a mod as it sounds. But the circuit isn't that complicated either.

And yeah, most people don't even touch assembly unless they're doing really low level embedded stuff or writing compilers.