Is it possible to design a brake check circuit that let’s you know when a rear light has failed.

Are there any off the shelf circuits?

I see you can get a brake warning light for when the brake pads are getting low.

A voltage current sensor might do it.

Tau.Neutrino said:

Is it possible to design a brake check circuit that let’s you know when a rear light has failed.

Are there any off the shelf circuits?

A car I owned back in the ’90s had one.

I would assume that all it needs is a small coil of wire wrapped around the brake wire. Brake pedal pressed, sensor circuit powers up, if it sees current, all good. If not, light comes on.
Sensing DC current isn’t as easy as sensing AC, but it can be done.

Tau.Neutrino said:

A voltage current sensor might do it.

A brick on the brake pedal is cheap & effective.

Tamb said:

Tau.Neutrino said:

A voltage current sensor might do it.

A brick on the brake pedal is cheap & effective.

Or back the car up to a reflective ssurface and press the brake pedal. They should both show or not.

What’s wrong with physical inspection? When you get the chance in a carpark somewhere to see your reflection in a window, just have a quick peek in your mirrors and check all your brake lights are working.

Dark Orange said:

Tau.Neutrino said:

Is it possible to design a brake check circuit that let’s you know when a rear light has failed.

Are there any off the shelf circuits?

A car I owned back in the ’90s had one.

I would assume that all it needs is a small coil of wire wrapped around the brake wire. Brake pedal pressed, sensor circuit powers up, if it sees current, all good. If not, light comes on.
Sensing DC current isn’t as easy as sensing AC, but it can be done.

with all the computers that have been in cars for quite a few years i guess it is done by them now. i had to put a resister in the circuit when I fitted my front protection as the original turn indicators were incandescent and the new ones LED. It would have shown a fault otherwise.

This $10 part will do it. Depending on how the car is wired, you may require one for each brake light.

https://www.ebay.com.au/itm/195039362079

JudgeMental said:

Dark Orange said:

Tau.Neutrino said:

Is it possible to design a brake check circuit that let’s you know when a rear light has failed.

Are there any off the shelf circuits?

A car I owned back in the ’90s had one.

I would assume that all it needs is a small coil of wire wrapped around the brake wire. Brake pedal pressed, sensor circuit powers up, if it sees current, all good. If not, light comes on.
Sensing DC current isn’t as easy as sensing AC, but it can be done.

with all the computers that have been in cars for quite a few years i guess it is done by them now. i had to put a resister in the circuit when I fitted my front protection as the original turn indicators were incandescent and the new ones LED. It would have shown a fault otherwise.

Surprisingly, that’s due to the blinkers using a circuit that relies on the current through the blinkers to bake them blink. If there’s not enough current, it doesn’t work. A “computer” wouldn’t care about current draw.

Dark Orange said:

JudgeMental said:

Dark Orange said:

A car I owned back in the ’90s had one.

I would assume that all it needs is a small coil of wire wrapped around the brake wire. Brake pedal pressed, sensor circuit powers up, if it sees current, all good. If not, light comes on.
Sensing DC current isn’t as easy as sensing AC, but it can be done.

with all the computers that have been in cars for quite a few years i guess it is done by them now. i had to put a resister in the circuit when I fitted my front protection as the original turn indicators were incandescent and the new ones LED. It would have shown a fault otherwise.

Surprisingly, that’s due to the blinkers using a circuit that relies on the current through the blinkers to bake them blink. If there’s not enough current, it doesn’t work. A “computer” wouldn’t care about current draw.

but it still shows up as a fault due to the computer reading it that way.

I will have a word with my auto electrician.

Tau.Neutrino said:

I will have a word with my auto electrician.

I would prefer a dc voltage current sensor pad that can just be placed over the pos neg wires.

Something like that.

Tau.Neutrino said:

Tau.Neutrino said:

I will have a word with my auto electrician.

I would prefer a dc voltage current sensor pad that can just be placed over the pos neg wires.

Something like that.

buy a couple of clamp meters.

JudgeMental said:

Tau.Neutrino said:

Tau.Neutrino said:

I will have a word with my auto electrician.

I would prefer a dc voltage current sensor pad that can just be placed over the pos neg wires.

Something like that.

buy a couple of clamp meters.

As it needs an ‘off the shelf’ solution, i’ll stop hunting for that simple circuit plan with a diode, a couple of resistors, an LED, and a transistor that popped into my head.

Tau.Neutrino said:

Tau.Neutrino said:

I will have a word with my auto electrician.

I would prefer a dc voltage current sensor pad that can just be placed over the pos neg wires.

Something like that.

That would be an elegant and simple solution if the brake lights didn’t use the chassis as the negative.

yes park somewhere with closed circuit television and then use the camera views to inspect it

The only way I can think of doing it would be fitting a coil in the wire to the lamp. Near the coil is a reed switch that detects a magnetic field. When the lamp fails all current to the lamp ceases and the magnetic field in the coil ceases. The reed switch detects the lack of magnetic field and allows current in the switch to flow to an input on the car’s brain or to a PCB of your choice somewhere in the cab

wookiemeister said:

The only way I can think of doing it would be fitting a coil in the wire to the lamp. Near the coil is a reed switch that detects a magnetic field. When the lamp fails all current to the lamp ceases and the magnetic field in the coil ceases. The reed switch detects the lack of magnetic field and allows current in the switch to flow to an input on the car’s brain or to a PCB of your choice somewhere in the cab

You could probably use a relay using a normally closedcontact. When current to the lamp ceases the relay closes the NC contact because its now de energised . The relay gets its power from the same circuit that powers the lamp