Car Blinker Lamp Detection

As the title would suggest I'm looking to be pointed in the right direction for figuring out how to detect if a car/truck blinker is lit or not by checking for the current and using it as an input on a digital pin. I've tried looking around quite a bit on youtube, google, and these forums for the past few hours but can't seem to find anything useful.

What I'm looking for.

lamp lit > send HIGH to digital input pin.
lamp off > send LOW to digital input pin.

I'm willing to figure out the circuit myself but I cannot seem to find even a similar circuit to understand this seemingly basic concept.

Micro Controller: Arduino Nano

An LDR (Light Dependent Resistor) will indicate whether light is shining upon it.

The more light, the lower the resistance, which is normally measured by Arduino using a voltage divider connected to an analog input.

jremington:
An LDR (Light Dependent Resistor) will indicate whether light is shining upon it.

The more light, the lower the resistance, which is normally measured by Arduino using a voltage divider connected to an analog input.

I looked into the detection of light but I want to be able to tap directly into the wires for the lamp (either negative or positive) and figure out if the lamp is lit or not.

How much current is flowing through the wire when the lamp is on?

Cars did this using a differential relay.

Many years ago I did this with a bare Reed relay with several turns of wire around the glass envelope . That wire was put in series with the lights .
The lamp current operates the Reed , which you can use as a digital input .
Note that by design your indicators will flash at a different rate if a bulb fails anyway

I think your best bet is to monitor the circuit current. This will check all the bulbs on it. In the US if a bulb fails it blinks typically tx its normal speed. This blink rate change is by federal law so a failed lamp can be detected from the driver seat. You need to know how much current each lamp filament draws and if they are different you can also determine which filament failed. You also need to understand automotive electronics for load dump, reverse battery, etc. This is also the ASIL classification QM & A-D with which is ISO 26262 ASILs and safety at the component level.

And .......Note too that bulb failure is rare , will your circuit be less reliable than the bulb ? Ie is the circuit more likely to give a false result than detect a failure of a bulb ? ( your circuit may have to work for a few years before a bulb breaks )

Yes
Always thought this was a good idea for all the lamps (legally required) and surprised that manufacturers don't do it as part of the management unit.
Going back years, if a lamp, flasher, failed, the rate of flashing changed and was a good indicator, or not.
For real confidence, you need to know if the lamp is showing, not just a change in current etc.
It's a legal requirement and MOT (UK) failure if the intensity isn't right as well.
As a quick check, pre driving, is to use the hazard lamp switch that activates all the lamps.
I've toyed with the idea of light to voltage sensors, but there is always the wiring problem, and testers might not like any modification.
LED lighting should be a lot more reliable, but you can still be had up for any lighting defect, rightly so, by the traffic police.
I wonder if a cheap wireless method might work with a display to test all or individually.
My latest vehicle seems to check everything, from seat belt to bonnet (hood), but not the lights.
Sounds like a useful project

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