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jnuaury
Joined: Feb 28, 2008 Posts: 161 Location: chicago
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JovianPyx
Joined: Nov 20, 2007 Posts: 1988 Location: West Red Spot, Jupiter
Audio files: 224
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Posted: Sat May 15, 2010 12:19 pm Post subject:
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Is this your design? I looked at the other thread, but I didn't see a reference to this schematic. I think I see what it's trying to do, but the region of control will likely be very narrow due to the gain properties of CMOS gates.
Note that by design, the 4016 and 4066 are _switches_, not variable resistors. They are meant to behave as you described.
For inline resistors that can be controlled by a voltage (or current) see H11F1, H11F2 and H11F3. These are opto isolator devices in which an internal LED illuminates a CMOS transistor, the amount of light (controlled by the current through the LED) controls the resistance. See the datasheets for the resistance range. _________________ FPGA, dsPIC and Fatman Synth Stuff
Time flies like a banana. Fruit flies when you're having fun. BTW, Do these genes make my ass look fat? corruptio optimi pessima
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richardc64
Joined: Jun 01, 2006 Posts: 679 Location: NYC
Audio files: 26
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Posted: Sat May 15, 2010 1:36 pm Post subject:
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JovianPyx wrote: | Is this your design? I looked at the other thread, but I didn't see a reference to this schematic. I think I see what it's trying to do, but the region of control will likely be very narrow due to the gain properties of CMOS gates.
Note that by design, the 4016 and 4066 are _switches_, not variable resistors. They are meant to behave as you described. |
It's on the second page, and is a fragment of synthmonger's 40106 VCO which, by all accounts, works. It's supposed to be a switched resistor, similar to switched capacitor circuits. It would seem to need a real resistor of 1K or so in series with the switch but frankly, I don't see how a variable switching rate translates to a variable resistance. I'd opt for a varying duty-cycle.
Edit:...unless the transistor at the 40106 input messes with the schmitt triggering thresholds, producing a variable width pulse _________________ Revenge is a dish best served with a fork... to the eye |
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JovianPyx
Joined: Nov 20, 2007 Posts: 1988 Location: West Red Spot, Jupiter
Audio files: 224
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Posted: Sat May 15, 2010 1:54 pm Post subject:
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Ah, thanks richardc64. Now it makes more sense. When I looked at it, I thought "chopper" as in a switched capacitor, but he called it a voltage controlled resistor so I thought he was trying to control the analog switch to have steady state variable resistance controlled by a voltage. The H11Fx ICs I mentioned will do that.
Yes, high speed on and off switching can emulate a variable resistor, but only for charge/discharge of a capacitor. And yes, PWM (or duty cycle as you say) usually works best in that case.
If this were applied to resonance of a SVF or other multipole filter, I think filter Q modulation would result - I have no idea how that would sound - but who knows, it might be interesting, especially if you control the chopper's frequency. _________________ FPGA, dsPIC and Fatman Synth Stuff
Time flies like a banana. Fruit flies when you're having fun. BTW, Do these genes make my ass look fat? corruptio optimi pessima
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mistercooper
Joined: Jul 17, 2006 Posts: 62 Location: Seattle
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Posted: Sun May 16, 2010 11:58 am Post subject:
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Try a vactrol or OTA. The 13700 datasheet has examples for floating vc resistors IIRC. |
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synthmonger
Joined: Nov 16, 2006 Posts: 578 Location: flada
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Posted: Mon May 17, 2010 5:25 pm Post subject:
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What are you trying to use the vcovr with? Any switching diode should work fine. I'm 100% the schematic is working fine.
If you build it correctly and use a multimeter across the 'switch' pins you'll get a resistance from 0-500k, which is why I call it a voltage controlled resistor. Oh and use a couple .1uf caps across the power rails and don't forget to ground the unused inverters.
I've used these in place of things that would normally require a variable resistor or an OTA with success, (wasp filter, state variable filters, phase shifters, etc). _________________ Youtube!
modular demos!
Whacky tunes! |
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e1999
Joined: Apr 25, 2019 Posts: 29 Location: naples
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Posted: Mon Sep 07, 2020 5:23 am Post subject:
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Was wondering if anyone has used this with single supply rather than +-12v as shown in the schematic?? |
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