[amluto]

Now I’m curious: what is the role of the 555 timer in a headlight?

I have a bit of a pet peeve about car lights (usually exterior lights that aren’t the headlights) that are visibly pulsed. They can be distracting. I think they should all be designed to operate either at silly frequencies that are genuinely undetectable by human eyes (30kHz?) or to genuinely operate at DC.

[lightedman]

"what is the role of the 555 timer in a headlight?"

Newer headlights use the 555 timer as a quick comparator to turn off the headlight when the corresponding turn signal is activated, and control the turn signal simultaneously.

[amluto]

Huh, I always imagined that newer cars would have a single CAN link to an ECU [0] in back, and that ECU would control all the lights near it. 555 timers may be cheap and robust, but monster wiring harnesses are not so cheap.

[0] Why do cars have special names for microcontrollers?

[lightedman]

"but monster wiring harnesses are not so cheap."

They aren't needed when the lighting is LED. The wiring harnesses going to more modern headlights are quite thin.

"I always imagined that newer cars would have a single CAN link to an ECU [0] in back, and that ECU would control all the lights near it."

They do but some are moving away because of the total lack of security and ability to compromise the CAN bus through the headlights to steal vehicles - read https://www.autoblog.com/news/vehicle-headlight-can-bus-inje... for what's going on there. They're too cheap to actually spend the money on real hardening so they're moving back to pure hardware control in many cases.

[daghamm]

Is this for a western car maker?

Haven't seen 555 in a commercial product with modern design for a long long time.

[roelschroeven]

> to turn off the headlight when the corresponding turn signal is activated

Wait what? Why is a headlight influenced by a turn signal??

I realize that American brake lights and turn signals are more intertwined than is reasonable, I've seen the Technology Connections Youtube video. Are you telling me something similar is going on with headlights?

[sangnoir]

> Wait what? Why is a headlight influenced by a turn signal

All cars with "Daylight Running Lights" (housed in the headlight assembly) turn them off for that side when the turn signal is active. I assumed this is to make the turn signal more obvious (as the change in brightness is more prominent).

[lightedman]

In many cars, the daytime running lights are also the headlights. Mine are in a 2013 Subaru Outback. However, they remain separate from my turn signals and do not deactivate when my signal activates.

For more modern vehicles, they have to turn off the LED/Laser-phosphor unit entirely because the lights design is too radiant and glaring for the turn signal to be seen. GMC and Ford big-ass trucks made within the last 5 years are an example.

[selcuka]

> Wait what? Why is a headlight influenced by a turn signal??

Some new cars, mainly luxury ones, dim headlights. It is to avoid blinding other drivers who may be looking at your turn signal.