Oscillator question.

[theavondon]

How hard would it be to make an oscillator that sweeps the pitch of the tone with an LFO. I had a musical idea, and it would need this.

[morange]

Not too hard. One way would be to find an oscillator whose frequency is determined by a potentiometer, and replace the potentiometer with an LDR. Then you control the resistance of the LDR with an led whose brightness is modulated by the LFO, like this LFO/LED combo, for example:


http://www.diystompboxes.com/smfforum/i ... c=74294.60

[theavondon]

Sweet tits. That doesn't sound tooooooo hard. But, I am inept.

[eatyourguitar]

its better to just ripoff the a little piece of the triwave picogenerator. it uses FET's instead of a LED/LDR. it runs on +9v. good to go.

[multi_s]

You could also use the popular IC such as CD4046 which is a PLL. All PLL s havea VCO section. So with i think about 3 (timing capacitor and resistor) parts you can make what you want using the 4046 even though your not making a PLL. It is already setup to be swept by a voltage so its a pretty good option. Chip probably costs less then 1 dollar.

[eatyourguitar]

if you do decide to use a LED/LDR, you can do it with no caps or resistors. just a 4049, LED/LDR, a pot for LFO frequency. you need an output cap but you dont need a timing cap. google 40106 oscillator. its the same thing as a 4049. the 4049 has 4 inverting buffers, the 40106 has 6.

I think you might be able to do it on a TL072 or TL074 also. I have seen triangle LFO's made from an opamp. you can make a oscillator from an inverting opamp just like you do it with inverting buffers in the 40106. you would still need that LED/LDR though.

[multi_s]

ya you dont need a resistor, just an LDR and a pot.

hrmm.

[theavondon]

ya you dont need a resistor, just an LDR and a pot.

hrmm.

light...dependent...ermmm

[eatyourguitar]

Semantics

[morange]

Light Dependent Semantics

[multi_s]

Light Dependent Semantics

winning.

[eatyourguitar]

Light Dependent Semantics

winning.