Looking for a design schematic to light 4-6 LEDs in parallel. I want to install it in a plastic heart, located inside a skeleton’s chest, part of a Halloween display. I’d like it to do a (beat-beat, short time off then (beat-beat). Repeat. If possible a way to adjust the speed.
operate at 9vdc
Thanks

 

Assuming you want all of the LEDs to blink on and off together, I'd use a CD4017 with a 555 timer as the clock. Or/skip the outputs to get the on-off-on-off timing you want and vary the frequency on the timer for your needs. You'll need to have the counter outputs drive a transistor to drive the LEDs.

 

Depending on the particular LEDs you intend to use, a series-parallel array will likely be more efficient (giving a longer battery life) than an all-parallel array.

 

Depending on the particular LEDs you intend to use, a series-parallel array will likely be more efficient (giving a longer battery life) than an all-parallel array.

Thank you

 

Schematic showing CD4017 with 2 LEDs. If you want 4 LEDs, add another MOSFET and pair of LEDs. For 6, use two strings of 3 and adjust the current limiting resistor accordingly.

 

You still need an oscillator to drive the 4017. And a pulldown on the gate.

 

I can't believe I'm saying this but I think the results would be better with a microprocessor to provide a more realistic throbbing. I've used one to throb an LED with a simple sine wave and it worked great. Hard on and off just doesn't look ... lifelike.

 

Schematic showing CD4017 with 2 LEDs. If you want 4 LEDs, add another MOSFET and pair of LEDs. For 6, use two strings of 3 and adjust the current limiting resistor accordingly.
View attachment 331318

So the diode are general switching and the 4017 requires a clock pulse. Will an adjustment to the speed of the clock pulse say from a 555 design easily change heart beat?

 

You still need an oscillator to drive the 4017. And a pulldown on the gate.

Example?

 

Hard on and off just doesn't look ... lifelike.

Normal Sinus Rhythm:

If one can duplicate this you have a real winner.

 

So the diode are general switching and the 4017 requires a clock pulse. Will an adjustment to the speed of the clock pulse say from a 555 design easily change heart beat?

Yes. The diodes can be 1N4148 or similar. I deleted the part number so I could put them closer together and forgot to add a note. You still have to add the 555 timer I mentioned in my first post. Also add a 10k pull-down resistor on the gate and decoupling caps.

You'll have to fiddle with the clock frequency because you only have 10 outputs to implement the desired pattern.

 

Yes. The diodes can be 1N4148 or similar. I deleted the part number so I could put them closer together and forgot to add a note. You still have to add the 555 timer I mentioned in my first post. Also add a pull-down resistor on the gate and decoupling caps.

You'll have to fiddle with the clock frequency because you only have 10 outputs to implement the desired pattern.

Not sure what you mean about the gate. Could you show an example ?
Thanks

 

Wouldn't the circuit in post #5 need an open output between D1 and D2 also D3 and D4 to produce (beat-beat, short time off then (beat-beat)?

If there aren't enough outputs to do the job, there is a way to change the timing of a 555 using the outputs of the 4017 to bring the timing circuit of a 555 to the positive rail.

 

Not sure what you mean about the gate. Could you show an example ?

This gives a frequency of about 10Hz, so the pattern would be on 0.2s, off 0.2s, on 0.2s, off 0.4s 0.3s.

I've never had problems with NE555 driving CMOS. If you do, you can add a pull up resistor on the output of the timer or use a CMOS version.

 

@dl324
Ok, I see what you are doing with that circuit...ignore what I said.

 

Normal Sinus Rhythm:
View attachment 331327
If one can duplicate this you have a real winner.

Well now that you point that out, maybe it wouldn't be that hard to simulate that. Counter hits one, LED full on. Two, full off. Three, LED on at 25%. Intervals four thru nine, LED off. Repeat. You could even use an RC tank to soften the on/off transitions.

 

View attachment 331331
This gives a frequency of about 10Hz, so the pattern would be on 0.2s, off 0.2s, on 0.2s, off 0.4s 0.3s.

I've never had problems with NE555 driving CMOS. If you do, you can add a pull up resistor on the output of the timer or use a CMOS version.

Looks good I’ll breadboard it. I’d like more time after second beat befor the two beat sequence repeats.
beat xxx beat xxxxxxxx beat xxx beat.
I’ll try this first. Doesn’t the 4017 need power at pin 16 and ground at pin 8?

 

I’d like more time after second beat befor the two beat sequence repeats.
beat xxx beat xxxxxxxx beat xxx beat.

You can play around with the number of counts that the LEDs are on and the frequency. Personally, I think I'd like the heartbeat to be slower.

Doesn’t the 4017 need power at pin 16 and ground at pin 8?

Yes. My schematic editor doesn't show explicit power connections for most parts - and I like it that way. I don't like the clutter power connections or decoupling caps. Anyone who knows anything will know that you need to connect power and supply appropriate supply decoupling.

 

Here's one way using CD4017B.
Generates about 50-100 beats per minute.
LEDs 20mA@2v each.
Uses 9v supply.

 

Normal Sinus Rhythm:
View attachment 331327
If one can duplicate this you have a real winner.

Close enough?



Edit: Revised NAND astable frequency, Moved CD4017B counter output connections, Changed C4.