How easy is it to make an LFO on a keyboard?

Bogus Noise · June 28, 2011, 06:58:13 PM

I mentioned the technique above, but basically connect C to one side of the pitch resistor. If it doesn't work, try the other side. If a toy has a pitch resistor, it can usually be easily found by prodding the circuit board with a slightly damp finger, one of the resistors will make the pitch go up or down. It's usually got a capacitor right next to it. To be honest though, I think at this point you probably have all the information you need to get going, and it's time to get your hands dirty with experimenting

It'll start clicking into place once you start playing about with it all!

bentoutofshape · June 28, 2011, 08:37:01 PM

Yes, I think you are right... I need to start fiddling about. Just needed a little dopey info.

...oh, just one more thing.. (columbo style) .. Where are the A and B points meant to go and why is there two A points? last question. I promise

Thanks to you all for all your help!

Bogus Noise · June 28, 2011, 08:45:21 PM

They're the power points and connect to the + and - points on the battery, as labelled on the drawing on the right. The only reason there's two A points is to save drawing another extra long line on the schematic - they both go to the same place!

Don't worry too much about this bit for now, but it's also good to find a way to connect it so that when you turn the toy off, the power to the LFO is cut as well. Sometimes this is as easy as connecting the positive lead just after the power switch, other times (like when the power switch is more software controlled) you need to probe the board with a multimeter to find a spot that gives positive voltage when the power is on, but not when turned off. Other times you may need to just add a dedicated switch to cut the power to the LFO.

bentoutofshape · July 01, 2011, 01:06:29 PM

An excellent amount of help you have given me here. Thanks a lot. Are there any keyboards that are known to be easy to bend and work with or are they pretty much all the same? battery powered ones of course

Circuitbenders · July 01, 2011, 02:30:46 PM

theres cheap toy keyboards for kids, most of which would probably respond pretty well to this kind of thing, and then theres most cheap Yamahas and Casios which would probably need an entirely different technique involving a new oscillator circuit.

tbone · July 01, 2011, 09:39:22 PM

I've never actually tried a 555 lfo with a shape and depth pot. I'll have to give it a try next time I use one.
Would you say they make a worthwhile addition to an LFO added to a keyboard? Worth the cost of the extra pots?

Dylan · July 02, 2011, 05:06:51 AM

I would think they'd be worth the $3 for a couple more parts. Much more warbly tones and cool sireny sounds.