I need a virtual hand to control a potentiometer based on the voltage

[solderman]

HI all
Sorry for bringing up this topic again, but I need some assistance to get where I want to.
I need a virtual hand to control a potentiometer based on the voltage given to the  virtual hand. Or in other words I need a Voltage controlled resistor. I have read trough everything in this thread the and  sub articles. http://www.diystompboxes.com/smfforum/index.php?topic=71832.0
I
The thing I'm trying to do is to let a 4017 sequencer control 8 separate adjustable voltages trough to a common point that will control the resistance as it was a liner 1M pot.  This "virtual" pot will then control the frequency of the simple XR2206CP signal generator chip.
This will give me a self playing organ with 8 separate notes in one tempo.
I have already tried the LED/LDR combo but it had no precission and the notes were all over the place. I'v also tried the JFET voltage controlled resistor but I haven't got that one to work. Probably cause I lack the skills to understand how to from the posts mentioned earlier.

Q- Any one that has an idée how I shall go about to achieve this virtual hand controlling a pot??

I will the I will feed the tones from the "organ" in to this "conductive pick " swell circuit (that has become a favorite of mine) to duck the signal from the organ and mix it with the dry signal from the guitar. That way the tones from the "organ" only will sound when the pick touches the strings. http://www.diystompboxes.com/smfforum/index.php?topic=76457.msg636611#msg63661

[slacker]

There's some info about making these voltage controlled over at the electro-music forums
http://www.electro-music.com/forum/viewtopic.php?t=10824&postorder=asc&highlight=xr2206cp

[R.G.]

Why not use eight real pots, and then use the 4017 to switch to different pots by switching either one JFET or one section of a CD4066 to each pot? It neatly sidesteps the issue of a virtual pot.

[valdiorn]

Two methods:
If you don't need a large range of resistance, a JFET can do the trick (use gate voltage to set the resistance from drain to source). Remember that this can cause distortion in the input signal if it gets too large.

You can use vactrols. I'm actually doing this myself for an amp project I'm building these days. Basically get a light dependent resistor (LDR), and a diode, glue them together and put heat-shrink over it. When you add more current through the diode, there is more light, and the resistance of the LDR decreases. I've made 4 so far and they all work great (you need some trimpots and shit to adjust for variances, this is not ideal for mass production)

[slacker]

Following on from what R.G. suggested you can use a CD4051 to sequence real pots, you just need a counter chip to drive it and a clock for the counter. Or use a CD4060 which is a counter with it's own clock.

[solderman]

Why not use eight real pots, and then use the 4017 to switch to different pots by switching either one JFET or one section of a CD4066 to each pot? It neatly sidesteps the issue of a virtual pot.

Thaks
Did not think about it that way. Of caus that will be the easyest way to let the 4017 trigger a switch to switch in a one at the time from a set of real pot's. Then I will have full controll.
Ill use the same setup as in your Juggler Ver 4.

[MikeH]

Why not use eight real pots, and then use the 4017 to switch to different pots by switching either one JFET or one section of a CD4066 to each pot? It neatly sidesteps the issue of a virtual pot.

A la zvex ringtone?

[R.G.]

Why not use eight real pots, and then use the 4017 to switch to different pots by switching either one JFET or one section of a CD4066 to each pot? It neatly sidesteps the issue of a virtual pot.

A la zvex ringtone?

Sure if that's what's in that. I never looked.

[solderman]

Why not use eight real pots, and then use the 4017 to switch to different pots by switching either one JFET or one section of a CD4066 to each pot? It neatly sidesteps the issue of a virtual pot.

A la zvex ringtone?

Yes but more like a vocorder type of sound. I got the ide'e while working with the Seek wha witch is a smiler type of setup with a 4017.

[solderman]

Hi

Would this work??

With my very limited knowledge of how to design thing I have drawn this.
The frequency of the XR2206 is controlled by altering the voltage drop on pin 7 to ground. The 1M pot fixes this and the higher the resistance goes the lower the frequency gets.

The 4017 will then trigger one transitor at the time to open between emitter and collector and by this connect the corresponding pot to ground and by this let the XR2206 generating the frequency corresponding to the resistance of that pot. Or is it the other way around that the trigger will close that connection between emitter and collector? In that case this will not work as I expect it.

What shall I do then? Use a FET and in that case how shall I orient D.G.S.

Thank's

[~arph]

You've drawn PNP's, but the text states a 2n5088 which is a NPN. Plus I believe you actually need NPN's here, but with the emitter to ground. Or use as RG stated JFET's or a 4066.

[solderman]

You've drawn PNP's, but the text states a 2n5088 which is a NPN. Plus I believe you actually need NPN's here, but with the emitter to ground. Or use as RG stated JFET's or a 4066.

OK schematic goof from me the arrow was meant to show an NPN. Not PNP.
How shall I orient the FET:s

EDIT:
Just bread boarded this setup wit 2N5088 and it works. I have uppdatet the schem with correct NPN:s and 100K instead of 220K.

[frequencycentral]

It's usual in sequencers to have the collector of each tranny go to lug 3 of the pot, lug 1 to ground, lug 2 via a 100K resistor to a summing amp, thence to the device to be controlled.

[solderman]

It's usual in sequencers to have the collector of each tranny go to lug 3 of the pot, lug 1 to ground, lug 2 via a 100K resistor to a summing amp, thence to the device to be controlled.

Hi. I guess so. The frequency of the XR2006 is controlled by a resistance to GDN. The higher the resistance the lower the pitch gets. That means that the I wanted it to work like the more CW the pot is the lower the resistance should be to produce the pitch I want.

[sean k]

I've never used them but a couple of transistor arrays might save some space. Several transistors in one package. I would have resistors either side of the pots and lower the pots value so its easier to tune to a note, say--- 36k, 25k trimmer, 36k---30k, 25k trimmer, 43k,etc, so each pot can be just used to fine tune a particular note then use a bunch of breadboard wires and a sixteen pin IC holder as a switching block; that way all you have to do is switch the wires instead of retuning the pots everytime you wanna change the sequence.

I'm just about to dig out a drum machine that switches between switch blocks to change sequencing patterns.

[dschwartz]

just an observation.. the clock for the 4017 can be way more simple than the oscilator you put...any square wave osc will do (for example using 2 and gates, or 2 inverters)