Designing a Reliable LED Flasher Circuit for Motorcycles

[jane will]

I’m working on a custom LED flasher circuit for a motorcycle and want to make sure it’s reliable and performs well. Instead of using a traditional 555 timer, I’m considering a microcontroller for more precise timing. 

What’s the best way to ensure the circuit can handle the voltage spikes and fluctuations commonly found in motorcycle electrical systems? Would adding things like a current limiter or overvoltage protection make a big difference? Also, any advice on testing it under real-world conditions would be really helpful!

[Zero999]

Why do you need precise timing?

Indicators must flash at between 60 and 120 times per minute.

https://www.gov.uk/guidance/mot-inspection-manual-for-private-passenger-and-light-commercial-vehicles/4-lamps-reflectors-and-electrical-equipment#section-4-4-4

That's a very wide margin for error.  A traditional astable with a calculated frequency of about 1.5Hz is more than good enough. The 20% tolerance of a cheap electrolytic capacitor is more than adequate.

[Analog Kid]

Instead of a 555, how 'bout a simple astable multivibrator to generate the square wave?



Much simpler; 2 transistors instead of 24. And as stated above, plenty accurate enough with cheap electrolytics.

[I wanted a rude username]

As Zero999 points out, the timing precision isn't all that important. But you may want a microcontroller for features, e.g. flash for two seconds then keep the light on until the brake lever is released again. The microcontroller-based solution may also be more robust against failure modes like the "noisy signal" you get when a well-worn switch is operated just at the point between off and on (but this depends on your code and on the safety measures you use such as a watchdog timer).

Automotive electrics is notoriously hostile, full of noise and voltage spikes. Definitely add reverse bias protection, make sure the regulator powering the microcontroller is rated to survive at least +30 V (and ideally more), and add noise filtering. Also make sure it's fused in some way.

On a bike it also pays to have a good enclosure with some water resistance. For my own mods I got away with some pretty ghetto solutions, like just wrapping the electronics in a plastic bag and adhesive tape and cramming it into a rear fairing, but you can't sell that ... it has to be robust and to look robust, to look like it's worth the money. Make sure there is a way to mount it (at least mount points and zip ties).

[Zero999]

Instead of a 555, how 'bout a simple astable multivibrator to generate the square wave?

(Attachment Link)

Much simpler; 2 transistors instead of 24. And as stated above, plenty accurate enough with cheap electrolytics.

In reality, you'll probably need more than just two transistors. I posted a similar circuit in the other thread. The extra transistors on the output sharpen up the output waveform and provide buffering for the load. At 12V, the transistor bases need diodes in series with them to protect against the reverse voltages when the capacitor discharges.


https://www.eevblog.com/forum/projects/motorcycle-flasher-circuit-validation/msg5786383/#msg5786383

[I wanted a rude username]

Oh, for some reason I assumed you meant a brake light flasher.

The LED indicator flasher is a solved problem (CF12ANL-01 for £8) but if it's a pet/school project then obviously go for it. You can learn as much or as little on it as you want, but just take it a bite at a time, get something simple working first ... all the other advice in my comment still applies in the general case.

[Kasper]

If this is for a brake light, consider adding an accelerometer to trigger it when slowing down.  Some bikes slow down pretty quickly without touching the brakes.