Voice Modulated 40106 Oscillato

Inventor

Hi all, I've come up with a way to modulate a 40106 oscillator (FM) using only two additional parts: a resistor and a capacitor. See the circuit below.

On the left is a microphone amplifier circuit. It's just two opamps in series, AC coupled, amplifying the weak signal of the mic, which is one of those little mic elements you can get for a breadboard or circuit board. That's all standard stuff, or my version of it, but what is really interesting is the 40106 modulation.

See the right part of the diagram. All you have to do is lift the ground lead of the capacitor and put a shunt 10k resistor and a seris 0.1uF input capacitor and drive it with a low impedance source - tada! Frequency Modulation!

I'm going to describe the circuit during this week's Les Hall Show, so tune in for a real treat (not to mention the way cool circuit that the osc is driving).

Les

Voice Modulated 40106 Oscillator.jpg

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the schematic

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Inventor · Posted: Mon Aug 22, 2011 10:25 am Post subject:

At the request of PHOBoS in chat, here is a more readable schematic. Enjoy!

Les

VMOSC.jpg

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the schematic

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Cynosure · Posted: Tue Aug 23, 2011 5:47 pm Post subject:

Great stuff. I can see this being very useful.

Any suggestions for modifying an external sound source using a mic? Kind of like a vocoder, but but just using the level to control a filter?

Inventor · Posted: Tue Aug 23, 2011 10:49 pm Post subject:

Well you can use it as a clock to other circuitry and then your other circuitry will also be voice modulated, that would be the main use. I found that doing so works if you keep the frequency unmodified, but as you divide down the frequency the voice signal fades. This makes sense as binary dividers have the feature of removing duty cycle variations.

Also it opens up the possibility of using a switched capacitor filter, something which I have not seen discussed here. Perhaps we should look into those circuits.

Les

kaputtpanzer · Posted: Sat Sep 03, 2011 3:12 am Post subject:

works great Very Happy

Thank you for sharing the schematic