Looking for a (Simple) LED Flasher Circuit

[Tchail]

Hello Braintrust!

Does anyone know of a (simple) circuit for blinking two (or more) LEDs on and off at the same time?

I know I could do this with an Arduino, but in this case I’m hoping to avoid the expense.

Any help would be appreciated!

-Tc

[EVApodman]

Try this.

https://www.youtube.com/watch?v=689c0jEjzok

[Zubie]

If exact timing is not an issue and all you are looking for is a blink, all you need are transistors, resistors, and capacitors (...and the LED of course). I recall seeing these kind of circuits using small wheat bulbs or other low voltage incandescent back in 70s science project exhibits, so the tech is not that sophisticated. The basic operation is akin to water backing up behind a dam (the capacitor) until the pressure becomes too great to be held back by the dam gate (the transistor) and discharges across the resistor all at once. The pressure drops and builds up again behind the gate and the process repeats. Because the output is representative of a repeating wave form, it can also be referred to as an oscillator circuit.

The timing can be calculated if one does the math; rate of buildup, breakdown charts for the transistor, etc., but you can find various articles online where such circuits are described and their performance posted.

A couple I found quickly
https://www.homemade-circuits.com/how-t ... istor-led/
https://blog.jongallant.com/2015/01/sim ... nking-led/
https://hackaday.com/2016/10/17/a-vinta ... d-blinker/

Another variation I've seen is 2 transistor circuits and this page describes one accessible as a student project (project 4:Model Mini-Flasher and project 5:Double lamp Blinker Circuit)
https://www.homemade-circuits.com/easy- ... -students/

I read that because of the physics of LEDs, you can't really make a circuit with just a capacitor acting as both the gate and the dam. The only simpler scheme would be to make use of a mechanical thermal distortion switch where the heat of the current distorts a wire to break the connection, but as the wire cools down the connection happens again repeating the cycle...i.e. an old christmas light blinker bulb.

[Rocketeer]

When I needed a circuit to flash 6 LEDs one second ON, one second OFF, I contacted Evan Designs and they built one for me. Cost me about $20.

[brt]

https://tenacontrols.com/product/new-mu ... rol-board/

$14.00 plus shipping.

[Tchail]

Adafruit makes an Arduino Trinket:

https://www.adafruit.com/product/3500

$8.95 + shipping.

[Tchail]

Okay - I just had a thought:

If I used a circuit for flashing a single LED, then I can use a transistor to blink as many LEDs in parallel as I need.

I just need to find a flasher circuit that runs at 4.5v.

(Most of the circuits I’ve seen have been 9-12v.)

[Zubie]

Okay - I just had a thought:

If I used a circuit for flashing a single LED, then I can use a transistor to blink as many LEDs in parallel as I need.

I just need to find a flasher circuit that runs at 4.5v.

(Most of the circuits I’ve seen have been 9-12v.)

I've seen some refs that state you can run a 555 timer as low as 4.5, although the norm for lower seems to be 5-6 (the latter because it's 4 standard battery Volts)
I recall that in college in my circuits course we ran thing like OpAmps, counters, timer chips, and number displays off a breadboard using 5V most of the time.

You should be able to build an R-C-Mosfet oscillator circuit that low but you will have to do the math yourself to find the right time constant for the R-C elements and then find a workable Mosfet threshold voltage for that particular set up. Given the relative prices, I'd go for the 555 timer as this is independent of another micro-controller and still fairly cheap overall. Any power supply you have envisioned for 4.5 (3AA[A]?) is probably fine substituted with a 9v battery case set up. Drain by LED's is surprisingly low so you should go quite a ways with that. If not, 9V transformers are all over the place and you probably have some just laying about doing nothing (I know I do).

[brt]

I read somewhere, a few years back, that the voltage drop across the 555 timer is 1.7 volts. So you realyy need 5 volts to run the average 3mm LED. Several colors require 3.3 volts, although some colors, less.

[brt]

Hello Braintrust!

Does anyone know of a (simple) circuit for blinking two (or more) LEDs on and off at the same time?

I know I could do this with an Arduino, but in this case I’m hoping to avoid the expense.

Any help would be appreciated!

-Tc

How about you buy a flashing LED and run a few regular LEDs in series? The other LEDs inseries will flash with the first one as the master.

[Zubie]

I read somewhere, a few years back, that the voltage drop across the 555 timer is 1.7 volts. So you realyy need 5 volts to run the average 3mm LED. Several colors require 3.3 volts, although some colors, less.

ic chips should be wired in such a way as they don't put a load on the circuit they control, only on the power supply itself. In the case of the 555 timer, the driving voltage (Vcc) is on pin 8, drawn through to the ground (pin 1...the red pins in the pic). This means you should always get the full V drop across the circuit with the LEDs and resistors.

It's not that you are getting something for nothing, the driving voltage will make up the difference of power lost to the control part of the circuit. It's pretty much the way all ic's work.

The lower limit to 5v is more a question of the design specs. I suspect that below 5v, particularly for the really cheap ones, the internal components will no longer work reliably (there's quite a bit of stuff inside the thing).