555 Timer Circuits

In some respects, it's a testament to how much the world of electronics has changed over the past ~25 years. It used to be that 555 was this Swiss-army-knife IC that you had to learn about. Multiple people published entire books about it!

Today, it's essentially obsolete. You're quite unlikely to find it in any competently-done commercial designs. Every analog trick you can do with it can be done more cheaply, more reliably, with better power efficiency, and with fewer external components using a modern MCU.

It's not that analog is dead, but it's solving different problems now. Including how to keep ultra-high-speed digital signals usable within the footprint of a PCB - which wasn't that much of a consideration in the golden days of the 555.

"You're quite unlikely to find it in any competently-done commercial designs."

You'll find them in tons of commercial designs - your modern headlights (which I manufacture) and off-road lights use them in droves. Short-timed lighting like automatic UVC sterilization lighting and such also still relies heavily upon a 555 timer just to act as the on/off switch for the power driver pushing the LEDs.

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.

"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.

> 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?

> 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).