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Circuitbenders Forum => Circuitbending discussion => BENDING TIPS => Topic started by: dirtycircuits on February 14, 2009, 02:32:35 AM

Title: Using LED's ?
Post by: dirtycircuits on February 14, 2009, 02:32:35 AM
I want to add some LED's to my projects -

Now I'm looking on the maplin website for 9 volt LEDs, and they all seem to be around 2 - 5 volts. What is the correct procedure for wiring up LEDs? Do I need to use a voltage regulator, or do people usually just use large resistors?

If so, do I need a separate resistor for each LED, or is it possible to just put one resistor on the Ground for all the LEDs?

I've trashed a few expensive LEDs by un-educated experiments, so it's time to ask for help and advice!

Also, say for example I have a drum machine... I've found an internal connection which will make an LED flash every beat - Now I need a circuit which will use this 'pulse' to drive a string of LEDs in a similar way to how expensive x-mas tree lights work, ie so that the string of LED's will 'flow' like running water. You know, like the lights you see in shopping malls at x-mas time.... I have a kids voice machine toy which has a hypnotic ring of flashing LED's where the light spins around the circle. The louder the volume the faster the light spins. Unfortunately the chip is in a black blob, so I can't see what it is, but if I could find something similar then that would be great...

Now is there a nice cheap cmos IC that I can use to do the job?

I thought it'd be really cool to do this with my HR-16. I've found a stable flashing LED point on one of the IC's, and I've got the whole week free to experiment...

Many thanks.............:-))
Title: Re: Using LED's ?
Post by: Gordonjcp on February 14, 2009, 07:20:29 PM
You need to use a series resistor with the LEDs.  Typically an LED wants about 20mA and has about 2v across it.  For 5v a 220 ohm resistor is about right.  You can use a transistor to switch higher currents - if you're driving it from existing circuits I recommend you do this.  You can also use a logic gate as a driver, something like a hex inverter.

For a chasing light you could use a 4017 decade counter, driving a string of LEDs.  To get a good "chase" effect, use about three or four outputs and several LEDs driven from each one - study videos of signs with chasey lights ;-)
Title: Re: Using LED's ?
Post by: dirtycircuits on February 15, 2009, 09:05:28 PM
Thanks for the reply,

So I feed my 'pulse' into the 4017's 'clock' input and it advances 1/10th. That's perfect, exactly what I was looking for!

Title: Re: Using LED's ?
Post by: goldenbaby on March 29, 2009, 06:13:55 AM
On my first project, the Talkin Whiz Kid, I put a green LED in series just before the speaker, and it flashes nicely, to indicate there is a signal going to the speaker, or the 1/4" output which switches.

Is this going to work on every speaker?  What if the voltage is too high just before the speaker, will placing a resistor in to tone it down going ruin the output coming out of the speaker?  Quieter?  Lower pitch?

Title: Re: Using LED's ?
Post by: Gordonjcp on March 30, 2009, 06:34:42 PM
That's going to do some pretty odd things to the sound ;-)

If you want an LED that flashes in time with the sound from the speaker, I recommend that you build a little driver circuit - basically a transistor, a resistor, a couple of capacitors and a diode - to isolate it all from the audio output.