How to test auto darkening rear view mirror

azureblue · Post by **azureblue** » 19 Jan 2018, 09:44

I have a used replacement rear view mirror, ready to go into my car. Is there a way to test it? I guess it would be putting DC voltage through the pins but does anyone know what voltage that would be?

Thanks

Post by **oragex** » 19 Jan 2018, 11:56

Maybe place a flash light just in front of it ? Or even a cigarette lighter

azureblue · Post by **azureblue** » 19 Jan 2018, 15:07

The mirror is removed from the donor car PC board. There are two pins on the back of the mirror itself, not the assembly or the PC board, that I want to test from. Before I solder it to the original PC board..... sorry I should have been clearer

Post by **RickHaleParker** » 19 Jan 2018, 15:49

The mirror is not in the wiring diagrams. Nobody can give you a safe answer. Your best course of action would be to measure the voltages on the PC board to get your answer.

Post by **abscate** » 19 Jan 2018, 16:06

Isn't it just a photocell which biases crossed polarizers? That doesn't need external voltage.

A strong flashlight should do the trick.

Post by **RickHaleParker** » 19 Jan 2018, 16:27

That doesn't need external voltage.

The LCD needs energy. The dimming is a unmasked LCD blocking light from reaching the mirror.

Post by **abscate** » 19 Jan 2018, 16:53

The Photocell provides the Potential - like a real old camera light meter using CdS - no batteries, the light generates the voltage needed to dim the LCD. Thats what mine looks like, but I don't have any more info than the visual

Post by **RickHaleParker** » 20 Jan 2018, 05:31

The mirror does have Photocells however, a Photocell is not a Photovoltaic cell.

Photocells are light sensitive resistors.
Photovoltaic cells aka Solar cells convert electromagnetic radiation into electrical energy.

Post by **abscate** » 20 Jan 2018, 14:35

I think I messed up the history of detectors. The standalone meters were Selenium, the CdS cells were the first battery operated ones.

I doubt they are using Selenium but some sort of PV would do this.