Two-Terminal LED Flasher

That's blinking marvellous.

Very nice. The highest current would be 0.3 ma and the LED wouldn't give any light at that level. Thanks, Rixter.

Ignoring the oscillator: with the 2N4401 turned fully on I make that about 14mA through the LED. How did you get to 0.3mA?

https://uk.rs-online.com/web/p/visible-leds/0585387/

I remember back when we were designing flasher cans for cars (direction indicators) and had to develop one that would work regardless of which terminal was connected to positive.

I was wishing then that we had the option to use solid state drivers, but were restricted to using relays so drivers could hear the sound of the unit, even with telltale lamps in the instrument panel.

I think the original ones had a heater resistor and a bimetallic strip. That should work with either polarity.

https://auto.howstuffworks.com/turn-signal2.htm

With a solid state unit, you can just feed it through a full-wave bridge rectifier.

Gosh, you have to design with the Blind Driver also, what with those anti discrimination laws in the US!

But really, I would always try to get a loud flasher cause in daylight your self canceling turn signal often did not, and it was nice to have it drive you crazy insted of the flasher driving all the other drivers mad.

Some cars used to have the 2 pin flashers and if any one element was burnt out they would do weird things like onlly blinkining when you hit the brakes. And they would back feed and make a circuit.

I was wishing then that we had the option to use solid state drivers, but were restricted to using relays so drivers could hear the sound of the unit...

I would think you could add a piezo device to get some sound, maybe drive it through a capacitor to get a click when the current stops and starts...

Both Ford and GM refused to allow piezo since to them it wasn't "failsafe", in that the flasher could be working with a failed piezo. SAE standards were also fairly specific at the time.

We used a series resistive component as the current sensor. Note that the standards also required >50% flash rate change if on of the lamps failed as a "teltale" to the driver.

Originally we manufactured our own relays.

We ended up developing a relay from SE Asia that cost less than 30% of the European components and less than 20% of the US components to stay competitive. We used those relays in assemblies for wiper controllers, power windows and so on. Meant around 1.5M pcs per year through our door

We exited flasher production in late '90's for the other manufacturing opportunities with better margin. Once we knew/controlled current direction, we were able to utilise different contact materials to minimise wear and material migration.

Thanks, that's good information. I can understand the safety aspect. As a beginning driver many years ago, I once pulled out in front of a car with the right turn flasher on. It turned out they were not turning, and fortunately, the only result was that I learned a lesson - don't assume the driver knows the thing is on.

I had a similar experience with a bus. Result: one badly bruised head (mine), a written-off Ford Escort (also mine) and a slightly dented bus (property of Reading Transport).

Where 2-terminal LED flasher is used?

This is for the turn signals on a car.

LEDs with a built in flash feature are available very cheaply.Only requires two wires.

Around $.09 each.

https://www.ebay.com/itm/100pcs-5mm-Red-Diffused-Flashing-Blinking-Leds-Light-12v-Resistor-Kit-USA-/322411980002

True, but that probably wouldn't work for turn signals. There are multiple LEDs in the indicator lamp usually, and both front and back indicator lamps need to be synchronized, and for 4-way flashers all need to be synchronized.