Blinking two LEDs in a pattern with passive components?

Thread Starter

bmbouter

Joined May 29, 2021
21
My son has this little toy that has two LEDs in it, one greenish-yellow and one Red. It blinks in this sequence that is one led on, off, on, off, on, off and then blinks the other in the same pattern and repeats. I took a slow-motion video of it here (1/8 speed).

https://youtube.com/shorts/sheK8LqldDE?feature=share

What sorts of schematic that runs on a coin battery (with minimal components) could do this?
 

Thread Starter

bmbouter

Joined May 29, 2021
21
How could they use a microcontroller in something so inexpensive? What sort of a microcontroller would that be? I imagined from a cost perspective, a passive component design would be cheaper, no?
 

Alec_t

Joined Sep 17, 2013
12,890
How could they use a microcontroller in something so inexpensive?
Because the simplest microcontrollers are also inexpensive to produce.
An example is to be found in a 'colour-changing LED', as used in some cheapo garden lights. Examine the 'LED' under high magnification and you will see inside it actually three LEDs (R,G,B) and also a tiny (about 1mm square) microcontroller which sequences the LEDs.
 

crutschow

Joined Mar 14, 2008
30,100
How could they use a microcontroller in something so inexpensive? What sort of a microcontroller would that be? I imagined from a cost perspective, a passive component design would be cheaper, no?
These days a small mircrocontroller is likely no more expensive to manufacture than a typical passive component.
 

dl324

Joined Mar 30, 2015
14,683
How could they use a microcontroller in something so inexpensive?
With a sufficiently small die and sufficient volume, the price can be low enough to be profitable. I have some LEDs with multiple colored LEDs and a microcontroller that blinks them in a fixed pattern; all housed in the same 5mm package. I have some LEDs with an IC that makes them blink mounted in the same 5mm package. In quantity 100, they cost me less than a nickel each.
What sort of a microcontroller would that be?
An inexpensive one.
I imagined from a cost perspective, a passive component design would be cheaper, no?
Passive components can't blink LEDs in set patterns. You require some logic to do that. A microcontroller is a convenient way to do that in terms of component count, cost, and area.
 

ThePanMan

Joined Mar 13, 2020
430
Using a 2N2222 transistor (which is not a passive component) a capacitor and an LED with a power source and you have JUST a blinking LED. If you want some sort of pattern you can't get there with just resistors, diodes and capacitors.
 

djsfantasi

Joined Apr 11, 2010
8,390
How could they use a microcontroller in something so inexpensive? What sort of a microcontroller would that be? I imagined from a cost perspective, a passive component design would be cheaper, no?
An ATTINY85 costs about $3 US. You’d need a programmer which is about $20 but you can use it for other ATTINY projects. A good deal if you already can code.

The toy manufacturer would pay much less for a microcontroller and would amortize the programming.

You can program it with a FREE Arduino IDE. But you’d need to learn coding and the use of the IDE and the programmer.

You could make it with a 74193 counter chip, a 74154 (or equivalent) decoder chip and 12 diodes, a couple of transistors and a few resistors, but… the logic chips alone would be more than $3. However, you wouldn’t need the programmer.

How much did you think it was going to cost?
 

Wendy

Joined Mar 24, 2008
22,931
I would be glad to help design something, that is not very complex. Binky LEDs are kind of my thing. How much electronics background do you have?
 

k1ng 1337

Joined Sep 11, 2020
584
You could do it with three 555 timers. One for each LED and one as a flip flop.

An ATtiny85 would be less space and can be programmed with an Arduino Uno. Then you can do as many colours and patterns as you like.

I recently made a lamp with one and even included the EEPROM memory for extra features. With a removable socket, I can reprogram the chip anytime. Lots of fun.
 
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Ya’akov

Joined Jan 27, 2019
5,998
An ATTINY85 costs about $3 US. You’d need a programmer which is about $20 but you can use it for other ATTINY projects. A good deal if you already can code.

The toy manufacturer would pay much less for a microcontroller and would amortize the programming.

You can program it with a FREE Arduino IDE. But you’d need to learn coding and the use of the IDE and the programmer.

You could make it with a 74193 counter chip, a 74154 (or equivalent) decoder chip and 12 diodes, a couple of transistors and a few resistors, but… the logic chips alone would be more than $3. However, you wouldn’t need the programmer.

How much did you think it was going to cost?
Hey, @djsfantasi don’t neglect the ATTiny13a which is more than enough for this project. Mouser has them in stock (in an SOP-8 package) at $0.75/ea, and this programmer is, also this adapter for the SOP package.The adapter bumps up the one-time programmer cost to ~24 bucks but it will also do DIP packages and be generally helpful, as you point out, in the future.
 
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