Controlling Resistance Digitally - what kinds of components can be used?
Bookmark this page:
 Yahoo!
 Google
 Windows Live
 del.icio.us
 digg
 Netscape
|
|
|||||||||||||
|
Posted by Patrick Keenan on September 18, 2008, 12:03 pm
Please log in for more thread options Hello All, I've recently posted on another topic, and thanks for the varied replies, which gave me the information I needed. I've another question regarding digital control of resistance. I have an application where I'd like to add digitally controlled resistance to pre-existing devices, where I can't modify anything except the resistance control itself. I can't alter the circuit in any other way. For an example, think of a "vintage" wah-wah pedal - in this case, pots do wear out so it's acceptable to replace that part - but that part only. One can't redo the circuit to match the pot, as that could alter the tone... I'm aware that there are digital potentiometers, but I have been finding that in a number of cases these just are not available in the values I might need to match the existing potentiometer, and/or may not be able to handle the current or voltage that might be present (such as in a guitar amplifier). So my question would be, what other kinds of resistive devices could be used to provide a digitally controllable resistance? Any hints on this are greatly appreciated. Thanks! Patrick Keenan | |||||||||||||
|
Posted by Jasen Betts on September 18, 2008, 10:32 pm
Please log in for more thread options a motorised dual gang pot in a servo circuit ? an ORP7 (or similar LDR) illuminated by a LED. (pwm at some ultrasonic rate) an ordinary pot driven by an off-the shelf R.C. servo. conbine two digital pots to give the range you want. Bye. Jasen | |||||||||||||
|
Posted by Bob Masta on September 19, 2008, 9:03 am
Please log in for more thread options
On 19 Sep 2008 02:32:49 GMT, Jasen Betts >> Hello All,
>> I've recently posted on another topic, and thanks for the varied replies, >> which gave me the information I needed. >> >> I've another question regarding digital control of resistance. I have an >> application where I'd like to add digitally controlled resistance to >> pre-existing devices, where I can't modify anything except the resistance >> control itself. I can't alter the circuit in any other way. For an >> example, think of a "vintage" wah-wah pedal - in this case, pots do wear out >> so it's acceptable to replace that part - but that part only. One can't >> redo the circuit to match the pot, as that could alter the tone... >> >> I'm aware that there are digital potentiometers, but I have been finding >> that in a number of cases these just are not available in the values I might >> need to match the existing potentiometer, and/or may not be able to handle >> the current or voltage that might be present (such as in a guitar >> amplifier). >> >> So my question would be, what other kinds of resistive devices could be used >> to provide a digitally controllable resistance? >
>a motorised dual gang pot in a servo circuit ? > >an ORP7 (or similar LDR) illuminated by a LED. (pwm at some ultrasonic rate) > >an ordinary pot driven by an off-the shelf R.C. servo. > >conbine two digital pots to give the range you want. All good ideas. One unusual addition is to use a CMOS switch to apply PWM to a fixed resistor, again at some ultrasonic rate. At low duty cycles there is less current through the resistor, so its value appears to be larger. This works especially well for circuits like wah pedals that are essentially low-pass anyway. For new designs, there is the advantage that you can have as many variable Rs as you want... and _they_all_track_perfectly with a single PWM signal. Works great for phaser/flanger circuits, where each stage adds another sliding notch to the output spectrum. Credit for this idea goes to Don Lancaster's "CMOS Cookbook"... strongly recommended! Bob Masta DAQARTA v4.00 Data AcQuisition And Real-Time Analysis www.daqarta.com Scope, Spectrum, Spectrogram, Sound Level Meter FREE Signal Generator Science with your sound card! | |||||||||||||
|
Posted by Patrick Keenan on September 19, 2008, 7:03 pm
Please log in for more thread options
> On 19 Sep 2008 02:32:49 GMT, Jasen Betts
> >>> Hello All,
>>> I've recently posted on another topic, and thanks for the varied >>> replies, >>> which gave me the information I needed. >>> >>> I've another question regarding digital control of resistance. I have >>> an >>> application where I'd like to add digitally controlled resistance to >>> pre-existing devices, where I can't modify anything except the >>> resistance >>> control itself. I can't alter the circuit in any other way. For an >>> example, think of a "vintage" wah-wah pedal - in this case, pots do wear >>> out >>> so it's acceptable to replace that part - but that part only. One can't >>> redo the circuit to match the pot, as that could alter the tone... >>> >>> I'm aware that there are digital potentiometers, but I have been finding >>> that in a number of cases these just are not available in the values I >>> might >>> need to match the existing potentiometer, and/or may not be able to >>> handle >>> the current or voltage that might be present (such as in a guitar >>> amplifier). >>> >>> So my question would be, what other kinds of resistive devices could be >>> used >>> to provide a digitally controllable resistance? >>
>>a motorised dual gang pot in a servo circuit ? >> >>an ORP7 (or similar LDR) illuminated by a LED. (pwm at some ultrasonic >>rate) >> >>an ordinary pot driven by an off-the shelf R.C. servo. >> >>conbine two digital pots to give the range you want. >
> All good ideas. One unusual addition is to use a > CMOS switch to apply PWM to a fixed resistor, > again at some ultrasonic rate. At low duty cycles > there is less current through the resistor, so its > value appears to be larger. This works especially > well for circuits like wah pedals that are > essentially low-pass anyway. > > For new designs, there is the advantage that you > can have as many variable Rs as you want... and > _they_all_track_perfectly with a single PWM > signal. Works great for phaser/flanger circuits, > where each stage adds another sliding notch to the > output spectrum. > > Credit for this idea goes to Don Lancaster's "CMOS > Cookbook"... strongly recommended! Thanks! As it happens, I have an old copy of the CMOS Cookbook downstairs, which some years ago I read until it started to fall apart. Yes, it's an excellent book. -pk >
> Bob Masta > > DAQARTA v4.00 > Data AcQuisition And Real-Time Analysis > www.daqarta.com > Scope, Spectrum, Spectrogram, Sound Level Meter > FREE Signal Generator > Science with your sound card! | |||||||||||||
|
Posted by John Fields on September 19, 2008, 8:29 am
Please log in for more thread options
wrote: >Hello All,
> I've recently posted on another topic, and thanks for the varied replies, >which gave me the information I needed. > >I've another question regarding digital control of resistance. I have an >application where I'd like to add digitally controlled resistance to >pre-existing devices, where I can't modify anything except the resistance >control itself. I can't alter the circuit in any other way. For an >example, think of a "vintage" wah-wah pedal - in this case, pots do wear out >so it's acceptable to replace that part - but that part only. One can't >redo the circuit to match the pot, as that could alter the tone... > >I'm aware that there are digital potentiometers, but I have been finding >that in a number of cases these just are not available in the values I might >need to match the existing potentiometer, and/or may not be able to handle >the current or voltage that might be present (such as in a guitar >amplifier). > >So my question would be, what other kinds of resistive devices could be used >to provide a digitally controllable resistance? > >Any hints on this are greatly appreciated. --- View in Courier: A7>-----------+
|
IN>------+--[ASW]---------+--->OUT
| | |
GND>---+-|----+ |
| | |
A6>----|-+----+ |
| | | |
| +--[ASW]---[R]---+ | | | | +-|----+ | | | | A5>----|-+----+ |
| | | |
| +--[ASW]--[2R]---+ | | | | +-|----+ | | | | A4>----|-+----+ |
| | | |
| +--[ASW]--[4R]---+ | | | | +-|----+ | | | | A3>----|-+----+ |
| | | |
| +--[ASW]--[8R]---+ | | | | +-|----+ | | | | A2>----|-+----+ |
| | | |
| +--[ASW]--[16R]--+ | | | | +-|----+ | | | | A1>----|-+----+ |
| | | |
| +--[ASW]--[32R]--+ | | | | +-|----+ | | | | A0>----|-+----+ |
| | | |
| +--[ASW]--[64R]--+ | | +------+ Where 'ASW' is an analog switch, or a solid state relay, or even a mechanical relay if you need the low contact resistance. JF | |||||||||||||
| Similar Threads | Posted |
| Controlling Resistance Digitally - what kinds of components can be used? | September 18, 2008, 12:03 pm |
| kinds of new breadboard online stores, the price is the half of your country | November 30, 2006, 12:23 am |
| Unofficial Phone, ,the most cheap mobile phones from china ,30 kinds today | November 30, 2008, 5:28 am |
| the theoretical formula for calculating the Equicalent Resistance of the Complex Resistance Network | October 19, 2008, 10:24 am |
| SMD components for a hobbyist | November 10, 2004, 2:09 am |
| Re: Help finding components | February 13, 2006, 6:12 pm |
| Oxidised components | February 17, 2006, 9:34 pm |
| Where to find these components? | April 2, 2006, 12:05 pm |
| Working with SMT components | August 7, 2006, 10:55 pm |
| Electronic components in the UK | December 27, 2007, 2:29 pm |
| PIN MESFET components | January 3, 2008, 5:23 am |
| digikey components | May 10, 2008, 9:47 pm |
| Components naming | November 9, 2008, 6:30 am |
| Controlling 12V from 5V | June 29, 2005, 3:35 pm |
| controlling | April 10, 2007, 6:25 am |
> I've recently posted on another topic, and thanks for the varied replies,
> which gave me the information I needed.
>
> I've another question regarding digital control of resistance. I have an
> application where I'd like to add digitally controlled resistance to
> pre-existing devices, where I can't modify anything except the resistance
> control itself. I can't alter the circuit in any other way. For an
> example, think of a "vintage" wah-wah pedal - in this case, pots do wear out
> so it's acceptable to replace that part - but that part only. One can't
> redo the circuit to match the pot, as that could alter the tone...
>
> I'm aware that there are digital potentiometers, but I have been finding
> that in a number of cases these just are not available in the values I might
> need to match the existing potentiometer, and/or may not be able to handle
> the current or voltage that might be present (such as in a guitar
> amplifier).
>
> So my question would be, what other kinds of resistive devices could be used
> to provide a digitally controllable resistance?