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.

There is still at least one niche for it: very simple circuits which requires >5v. Using 555 lets you skip the regulator and drivers.

But even there, it's high Iq limits its applicability.

I think it's more that the 555 is basically the heart of hysteretic controller in a box, but it doesn't have the other stuff you need.

https://en.wikipedia.org/wiki/Bang–bang_control

There's still plenty of analog control out there, it's just all hidden away as parts can integrate the sensor, controller and actuator, all in one magic IC. And it can definitely be lower power and cheaper, in volume. The main weakness is the NRE is higher than the typical MCU project so it's not really seen in low volume or hobby level stuff.

I'd guess that a 555 is also tougher than a microcontroller. I'm putting together an HV supply and thought about using a microcontroller but opted for a 555-based oscillator. Either one won't survive HV but I think the 555 will handle stray charges better.

"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.

Can you recommend books/courses that cover this new approach you’re talking about?

Yep, came to this realization awhile ago, about the superiority of digital in many cases, when I had an amplifier project with a dizzying number of requirements and a very large dynamic range and (log) linearity needed. Ended up using a few ranges of ADC’s, doing the required mathematical transform on a MCU, then outputting the required voltage with a DAC. The previous gen was some fairly complex circuit designed by a smart analog guy and still wasn’t nearly as performant

There's still room for synchro and servo theory I learned in the Navy but I really like the digital world a lot, so flexible.

Modern mucus are surprisingly fault tolerant. Just saying. It’s not like the bad old days where if you sneezed at a cmos chip it would probably be fried. I’m not sure how that stacks up to a 555 though.

Even in jellybean analog, almost everything you can do with a 555 timer you can do with a quad comparator. And more. Over a bigger voltage range, too. It’s usually a design smell to see a 555 used for anything in a professional design, even from before the tiny mcu era.

It makes a nifty missing pulse detector, though.

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.

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?

Is this for a western car maker?

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

"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.

Its kind of interesting: the 555 is such _horrible_ timer. It can't do a 50% duty cycle without extra BOM parts, even more parts to make a real PWM out of it, and it has terrible temperature and voltage stability. But somehow it persists.

My mucus is about as fault tolerant as it ever has been. Sometimes it gets really thick if the weather is dry or I'm sick, but otherwise I haven't noticed any difference. I find that drinking water helps.

> 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?

lol. Eventually, spellcheck will eliminate my need to type altogether.

> 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.

Bob Pease has a pretty scathing opinion: https://www.electronicdesign.com/technologies/analog/article...

“Hi, Jeff H., I have almost never used a 555. Maybe never? I use op-amps, LM324's, LM311's, LF356's. I use 74HC04's and 74C14's but not 555's. I've used ECL fast logic, and discrete transistors. But the 555 just does not do anything precise, or even semi-precise, that I need done. So that's one thing I can "share" - my favorite circuit to use a 555, is: a blank piece of paper. Never touch the things. Go ahead and print that. / rap”

> 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).

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.