Need help designing a schematic - LED pedal

[davidjnichols]

My 5 year old son has taken an interest in my pedal building.  He doesn't play guitar, but I had a cool idea for a "pedal" to build for him.  But I need your help.

I have a few dozen 3mm LEDs laying around that I want to use.  I want to create a pedal with an on/off switch and a bunch of LEDs, so it basically just lights up when you switch it on.  Also, I just finished building a few EA tremolo pedals that have the flashing LEDs that correspond to the rate of the tremolo.  I'd like to put one knob on the pedal that would change the rate at which the LEDs flashed, just like in the tremolo schematic.  If possible, I would also like the LEDs to pulse more than just flash.  

Here's the EA tremolo schematic and the wiring diagram that explains the flashing LED:
Schem: http://www.generalguitargadgets.com/pdf/ggg_eat_sc_improved.pdf?phpMyAdmin=4a28f86a515b7883e7bc35a68d4e7b6d&phpMyAdmin=78482479fd7e7fc3768044a841b3e85a
Wiring Diagram: http://www.generalguitargadgets.com/pdf/ggg_eat_mods.pdf?phpMyAdmin=78482479fd7e7fc3768044a841b3e85a

When wiring multiple LEDs, can I simply wire a few dozen of them in series?  Also, which parts of this EA Tremolo schematic correspond to the pulse of the effect?  Any idea on how to get them to pulse rather than just flash?

I think this could be a fun project and any help I can get would be greatly appreciated.  Thanks!

David

[davidjnichols]

Anyone?

[R O Tiree]

I recently designed and built a circuit for my daughter that had several LEDs  flashing in sequence - binary counter with the LEDs out of sequence, so it looked fairly random. I could re-hash it if you'd like?

[davidjnichols]

I recently designed and built a circuit for my daughter that had several LEDs  flashing in sequence - binary counter with the LEDs out of sequence, so it looked fairly random. I could re-hash it if you'd like?

That would be amazing!  Thank you. 

[R O Tiree]

The way the circuit worked was to have a master on/off switch and an additional momentary switch to reset the counter and start the oscillator. If that's what you'd like, then I can send you the schem/PCB art as is. If, however, you want just one switch, then I'll have to make a couple of changes. Let me know?

[PRR]

> multiple LEDs, can I simply wire a few dozen of them in series?

Red or Green LEDs need roughly 2V each. Plus some overhead for a current-control resistor, say 30%.

So if "few dozen" is 36 LEDs, you need 36*2V= 72V, plus 30% resistor-drop, is 94V.

94V batteries are expensive.

I would not put a 94V battery in a child's toy. (Actually _I_ might, but you probably shouldn't.)

Assuming 9V batts, three in series is reasonable. More than that, wire 3 and a resistor, another 3 and a resistor, parallel the chains.

There's an on-line calculator. While a sharp 5yo can do the math, the calc helps lead you to more-likely solutions.

EA trem osc is fussy. Lovely smooth waveform is wasted for a blinky-box. Use 555 chip.

> pulse more than just flash.

Not sure what that means. If you want a "smooth" wave rather than hard on/off, there are a million 2-opamp triangle-wave oscillators. Generally need a 3rd opamp to buffer the tri-wave. If more than one or two parallel strings, it needs to be a power buffer; TIP120 is as good as any.

[Gurner]

with 36 LEDs in play I wouldn't even consider a 9V battery   ....assuming 10mA LED current through 18 'strings' of 2 LEDs in series ...that's 180mA which a 9V battery isn't going too take kindly too.

[deadastronaut]

cheesey little led 'fade on, fade off circuit..if it helps..