# Blinking two LEDs in a pattern with passive components?

#### 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).

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

#### BobTPH

Joined Jun 5, 2013
5,227
A microcontroller plus a couple of capacitors and resistors.

#### 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.

#### Dodgydave

Joined Jun 22, 2012
10,361
That will be a Blob Chip and a RGB led like those in garden lights, and some impact sensor like a spring.

#### 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.

#### BobTPH

Joined Jun 5, 2013
5,227
Passive components cannot blink LEDs at all, let alone in a sequence like that.

Bob

#### 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.

#### Audioguru again

Joined Oct 21, 2019
4,792
That will be a Blob Chip and a RGB led like those in garden lights, and some impact sensor like a spring.
Kid's shoes also have them.

#### 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. Last edited: #### 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.