My simple solution would be a D to A (Digital to Analog chip driven by an Arduino or similar micro-controller. I am still not sure what your VCO is? I see VCO and think Voltage Controlled Oscillator. A Google of Arduino Digital to Analog should bring up hits including code samples. Another possible is a basic signal / function generator capable of a sine wave, one that has a VCO input.

Ron

 

My vco is a 555 chip. For now I'm staying analog. I've ordered a Mitch Electronics vco kit. I hope it comes with instructions as their web doesn't seem to be working. I also ordered their little audio amp kit. my soldering is much improved

 

OK now I know that your VCO is what I thought, voltage in and frequency out including a sine wave. The Mitch Site seems to be down but I found it here from another distributor. So you go from a voltage to a frequency with an output frequency proportional to input voltage. How do you plan to read the frequency out?

Ron

 

With a speaker. Believe it or not here's what I'm doing. I'm using a roller on a violin instead of strings to measure the force a student uses. It's too hard for them to hear intensity with a string. With a VCO intensity is output as lower pitch. Keeping the same intensity throughout a whole bow is very difficult and hard to understand. The physics may speak for itself but some things work better than words. Eventually I'll mount LC's under the feet of the bridge of a violin and perhaps analyse players bowings using a digital readout into an arduini or Pi. The HX711 should make that quite easy. For the present project I'll mount the INA125 and 555 on the violin with an amp, battery and small speaker so there is no trailing wire. Meanwhile, attached is a guy's idea of how to turn a 555's square wave into a sine.

 

An IC, a CD4046 PLL includes a VCO that can be directly controlled by a DC level. And it produces a nice sine wave by design. Made by several suppliers.

 

I've ordered a CD4046 PLL. Thanks, looks very useful. Attached the breadboard with INA125 and 555 circuits as well as the cheap 433Mhz transmitter on my violin (so it's now wireless). Here's a link to an mp3 of it operating https://jumpshare.com/s/hJJbyd42ccqRiAvjktf9 . The first and last part of the sound is a 87Hz hum (actually the weight of the roller on the loadcell). In the middle is some seconds of a slow bow (not very even). What should I do to get rid of the hum? Thanks.