LED Dominos Using a 555 Timer -- The Learning Circuit 63

LED Dominos Using a 555 Timer

The Learning Circuit | element14 presents | Project Videos

In the last lesson, we learned what happens inside a 555 timer to make it work. In today’s episode, Karen uses 555 timers to make LED “dominos”. Each unit has an LED connected to the output of a 555 timer and an LDR attached to the trigger. When the LDR senses light, the 555 is triggered turning the light on for a brief period of time. When multiple units are placed in a row, each one triggers the next. The duration that each light is on is determined by an “RC circuit” made of a resistor and capacitor. Changing their values can change the duration that the light is on.

The idea for this project came from a video made by Randy Elwin back in 2011. Karen uses his idea to make a similar device to show off using a 555 timer in a monostable circuit. (Learn more about monostable circuits in the NEXT lesson about 555 timers.) Shining a light on the LDR triggers Pin 2 and the 555 is “set” on. The RC circuit connected to pins 6 & 7 eventually cause the voltage at Pin 6 to go High enough to reset the 555, turning the LED off.

Bill of Material:

Product Name	Manufacturer	Quantity	Buy KitBuy Kit
Electrolytic Capacitor, Miniature, 100 µF, 50 V, HE Series, ± 20%, Radial Leaded, 8 mm	nichicon	1	Buy NowBuy Now
Ceramic Disc Capacitor, 0.01 µF, 100 V, ± 20%, 5 mm	Vishay	1	Buy NowBuy Now
LM555CN - Timer, Oscillator & Pulse Generator IC, TTL Compatible, Astable, Monostable, 4.5 V to 16 V, DIP-8	On Semiconductor	1	Buy NowBuy Now
Through Hole Resistor, 220 ohm, 400 mW, ± 1%	Vishay	1	Buy NowBuy Now
Through Hole Resistor, 10 kohm, 250 mW, ± 1%	TE Connectivity	2	Buy NowBuy Now
Photo Resistor	Adafruit	1	Buy NowBuy Now
Prototype Board, 25 x 15 grid, 1.6 mm, 72 mm, 47 mm	Multicomp	1	Buy NowBuy Now
LED, Cool White, Through Hole, T-1 3/4 (5mm), 20 mA, 3.2 V	Cree	1	Buy NowBuy Now
9V battery snap, flexible	Multicomp	1	Buy NowBuy Now
Battery, 9 V, PP3, Alkaline, 565 mAh	Pro Elec	1	Buy NowBuy Now
Hook-up Wire Spool Set - 22AWG Solid Core - 10 x 25ft	Adafruit	1	Buy NowBuy Now

Top Comments

Parents

beacon_dave over 5 years ago

Another great Learning Circuit episode.

The original design looks like it uses the TI TLC555CP CMOS version of the 555 timer which looks like it works down to a supply voltage of 2v, which should work off the 3v button cell shown.

To keep e14mindi happy ( https://www.element14.com/community/message/285783/l/get-a-gold-star-by-citing-your-sources#285783 ) I think the Randy Elwin video referred to is perhaps this one:

'Le Dominoux'
https://www.youtube.com/watch?v=PQOjkuJtBfM
which appears to have been an entry for the 2011 555 timer contest.

It is worth a watch anyway to see some of the scaled up versions in action.
Did someone mention Xmas lights ?
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beacon_dave over 5 years ago

Another great Learning Circuit episode.

The original design looks like it uses the TI TLC555CP CMOS version of the 555 timer which looks like it works down to a supply voltage of 2v, which should work off the 3v button cell shown.

To keep e14mindi happy ( https://www.element14.com/community/message/285783/l/get-a-gold-star-by-citing-your-sources#285783 ) I think the Randy Elwin video referred to is perhaps this one:

'Le Dominoux'
https://www.youtube.com/watch?v=PQOjkuJtBfM
which appears to have been an entry for the 2011 555 timer contest.

It is worth a watch anyway to see some of the scaled up versions in action.
Did someone mention Xmas lights ?
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makerkaren over 5 years ago in reply to beacon_dave

I think you're right about him using a CMOS 555. I didn't have any around and didn't have time to wait for some to get shipped to me, so I worked with what I had. Great observation!
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