I've recently started circuit bending (the process of taking something that makes sound and changing its components to make a sound the thing wasn't supposed to make). I am familiar with Low Frequency Oscillators and being able to change the voltage...maybe current considering its a wave, not quite sure there...And I am able to do that mechanically by turning a pot so as the resistance changes the pitch of the sound changes.
Is there a way to change the pot out with something like an LFO so that I don't have to turn the pot. The resistance would change automatically. For example it would sweep from 0 ohms to 1Mega ohm and then back again. Or ramp from 0 ohms to 2k ohms. etc
Thanks
Variable resistor idea question for circuit bending
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thejunkyardcatalyst
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Chris Smith
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Leon Theramin and Robert Moog.
http://en.wikipedia.org/wiki/Theremin
http://en.wikipedia.org/wiki/Robert_Moog
http://en.wikipedia.org/wiki/Theremin
http://en.wikipedia.org/wiki/Robert_Moog
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thejunkyardcatalyst
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Bob Moog is my Hero
Those guys are incredible for what they have done. Bob Moog for what he has done and who he is/was. I'm talking more about http://en.wikipedia.org/wiki/Circuit_be ... uitbending
I'm wondering if I can replace a pot with an automated variable resistor. Simply remove the pot and add an oscillator or something of thats sort.thanks
There are digitally controlled Pots but then you would need to drive it with a counter or similar digital word generator. Search on "Digital Pot"
If you want to control it from an analog signal, that requires more work. In this case you might be better off replacing the pot with a transistor. Input your signal to the base, bias for the correct range of collector current for your given base drive, pass the current through a series resistor (emittor to ground and sense the variable voltage at the emitter (wiper of pot was here). Exact wiring depends on circuit design and source voltages, some variations exist.
Alternatively, you can do an A/D conversion then use the digital pot but that results in a more expensive and complicated design.
Some good basics here
http://www.maxim-ic.com/appnotes.cfm/ap ... umber/1956
http://www.maxim-ic.com/appnotes.cfm/ap ... umber/3417
If you want to control it from an analog signal, that requires more work. In this case you might be better off replacing the pot with a transistor. Input your signal to the base, bias for the correct range of collector current for your given base drive, pass the current through a series resistor (emittor to ground and sense the variable voltage at the emitter (wiper of pot was here). Exact wiring depends on circuit design and source voltages, some variations exist.
Alternatively, you can do an A/D conversion then use the digital pot but that results in a more expensive and complicated design.
Some good basics here
http://www.maxim-ic.com/appnotes.cfm/ap ... umber/1956
http://www.maxim-ic.com/appnotes.cfm/ap ... umber/3417
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Chris Smith
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In a way the Theramin does that through body capacitance and the antenna.
Have you considered a Cad cell and reflected light?
A cad cell is a resistor, and the ambient light and your hand near or waving over it will adjust the resistance.
So will fans and light, ambient light from morning to noon, and even heat convection, body heat, and dry vs humid wind in the room,.... with a gain factor to make it more sensitive.
Also different colors of light, modulated light, strength of light etc can all equal a variable resistance value that is unique.
Also the 555 as a capacitance input can vary a resistor value output which can be set random, to body capacitance, or even heat pick up and wind values.
Have you considered a Cad cell and reflected light?
A cad cell is a resistor, and the ambient light and your hand near or waving over it will adjust the resistance.
So will fans and light, ambient light from morning to noon, and even heat convection, body heat, and dry vs humid wind in the room,.... with a gain factor to make it more sensitive.
Also different colors of light, modulated light, strength of light etc can all equal a variable resistance value that is unique.
Also the 555 as a capacitance input can vary a resistor value output which can be set random, to body capacitance, or even heat pick up and wind values.
to respond to your actual question, yes, you can replace the manual pot with a digital one but be aware that the digital pots aren't made to carry a lot of current. You might have to do some analysis of the existing circuit to determin max current. You might have to add a limiting resistor on the wiper. maxim makes a lot of digital pots. they are very easy on samples - just ask and they may send you some freebees...
I agree that for analog control, it might be easier to use a transistor (or op amp?) to vary the voltage. note that you might not be able to get full range with transistors - maybe with fets but I think a rail-to-rail opamp could be made to work better.
On the whole, I think the digital pot has the most potential, especially if you can use some sort of digital control.
I agree that for analog control, it might be easier to use a transistor (or op amp?) to vary the voltage. note that you might not be able to get full range with transistors - maybe with fets but I think a rail-to-rail opamp could be made to work better.
On the whole, I think the digital pot has the most potential, especially if you can use some sort of digital control.
Cad cell??? I think you mean CdS or Cadmium Sulphide. A good option.
http://www.selcoproducts.com/cfm/photoc ... ls_Cat.pdf
http://www.selcoproducts.com/cfm/photoc ... ls_Cat.pdf
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Chris Smith
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Oh cad cell, now you're talking he he.
I have an old one from way back that i used for measuring fan
RPM's on an old fan i used to use that i liked a lot and didnt want
to throw out even though it was old and needed constant attention
to the bearings (oiling twice a year).
I used a resistor and battery with the cad cell shining a laser
'through' the fan blades so when it rotated it would break the beam
getting to the cad cell. The change in voltage level was then
picked up by a frequency counter so all i had to do was divide
by 3 (three fan blades) to get the RPM.
When the rpm's dropped below a certain level i would oil the fan
again...it was a pain though because the motor had to be taken
apart.
Finally got tired of doing that and threw the dang though out he he.
The CdS cell (cad cell for short) really came in handy though and
i'd do it again if i had to measure RPM again.
BTW side topic, laser pointers make really good light sources for
motion detection like this as long as nobodys eyes can get in the
light path.
I have an old one from way back that i used for measuring fan
RPM's on an old fan i used to use that i liked a lot and didnt want
to throw out even though it was old and needed constant attention
to the bearings (oiling twice a year).
I used a resistor and battery with the cad cell shining a laser
'through' the fan blades so when it rotated it would break the beam
getting to the cad cell. The change in voltage level was then
picked up by a frequency counter so all i had to do was divide
by 3 (three fan blades) to get the RPM.
When the rpm's dropped below a certain level i would oil the fan
again...it was a pain though because the motor had to be taken
apart.
Finally got tired of doing that and threw the dang though out he he.
The CdS cell (cad cell for short) really came in handy though and
i'd do it again if i had to measure RPM again.
BTW side topic, laser pointers make really good light sources for
motion detection like this as long as nobodys eyes can get in the
light path.
LEDs vs Bulbs, LEDs are winning.
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Chris Smith
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- Location: Bieber Ca.
I use the 780 nm and 920 nm [or even the 1100 nm] lasers for that so its less damaging to the eye should you stare into them.
Being in the IR range, it doesn’t affect the color part of your eyes as much as the visual spectrum lasers do, and a lot of the beams energy is absorbed in the water in your eye, diffusing the energy out over a larger part of the eye.
Being in the IR range, it doesn’t affect the color part of your eyes as much as the visual spectrum lasers do, and a lot of the beams energy is absorbed in the water in your eye, diffusing the energy out over a larger part of the eye.
Hi Chris,
That's not a bad idea, but i wasnt about to go out and buy another
laser just to measure the fan speed when i already had a red one
sitting around doing nothing. Im sure you could understand that.
At one time i was considering installing an ir LED/detector on the
fan itself and have it connected to my freq counter to have a readout
24/7 (dont use the freq counter that much anyway so at least it would
be doing something) but then i decided just to chuck the fan and buy
a new one ... cost about $10 brand new he he. Still would have been
fun i think.
What i'd also like to do maybe is build a LED/detector pair mounted
to a "C" shaped arm and have it plug into the freq counter. I could
then just pick it up and position the "C" around the fan side exterior so
that the LED light path would shine 'through' the fan blades. This would
make measurements on any fan quick.
I find that once they get old they dont like to turn on one day after they
have been off all night, because the bearings are dry. The speed
seems to indicate the state of the bearings pretty well, so measuring
the speed would tell if any fan needed attention.
That's not a bad idea, but i wasnt about to go out and buy another
laser just to measure the fan speed when i already had a red one
sitting around doing nothing. Im sure you could understand that.
At one time i was considering installing an ir LED/detector on the
fan itself and have it connected to my freq counter to have a readout
24/7 (dont use the freq counter that much anyway so at least it would
be doing something) but then i decided just to chuck the fan and buy
a new one ... cost about $10 brand new he he. Still would have been
fun i think.
What i'd also like to do maybe is build a LED/detector pair mounted
to a "C" shaped arm and have it plug into the freq counter. I could
then just pick it up and position the "C" around the fan side exterior so
that the LED light path would shine 'through' the fan blades. This would
make measurements on any fan quick.
I find that once they get old they dont like to turn on one day after they
have been off all night, because the bearings are dry. The speed
seems to indicate the state of the bearings pretty well, so measuring
the speed would tell if any fan needed attention.
LEDs vs Bulbs, LEDs are winning.
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Chris Smith
- Posts: 4325
- Joined: Tue Dec 04, 2001 1:01 am
- Location: Bieber Ca.
Al
The way I solve my fans and their bearings drying up is to get a hypo and needle used for ink replacement and fill it with light oil and kerosine for a thinner. 50/50 Also disolve some lithium grease in kero.
Then I take the fan out side, open it up, and using the needle I flush a few dozen drops right at the shaft base and bearing and let it soak into the bronze bearings. I also like to run it full bore while lubing it.
This usually cures the problem til the next year comes around and the bearings dry out once more.
If the fan is my favorite I disassemble it and use lithium grease on the bearings, and this makes it last for two years or more. If you really want to get fancy and the bearings come out, you boil them in oil or lithium grease. Cures them for a dozen years, or life, which ever comes first.
As to a better or safer laser, old CD ROMS have a slightly higher frequency laser.
They run 780 nm. Almost IR.
Also today’s white Leds should do the trick.
You still can’t stare it in the eye but a flash across the eye is less traumatic than the 630/640 hand lasers pointers.
The way I solve my fans and their bearings drying up is to get a hypo and needle used for ink replacement and fill it with light oil and kerosine for a thinner. 50/50 Also disolve some lithium grease in kero.
Then I take the fan out side, open it up, and using the needle I flush a few dozen drops right at the shaft base and bearing and let it soak into the bronze bearings. I also like to run it full bore while lubing it.
This usually cures the problem til the next year comes around and the bearings dry out once more.
If the fan is my favorite I disassemble it and use lithium grease on the bearings, and this makes it last for two years or more. If you really want to get fancy and the bearings come out, you boil them in oil or lithium grease. Cures them for a dozen years, or life, which ever comes first.
As to a better or safer laser, old CD ROMS have a slightly higher frequency laser.
They run 780 nm. Almost IR.
Also today’s white Leds should do the trick.
You still can’t stare it in the eye but a flash across the eye is less traumatic than the 630/640 hand lasers pointers.
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SETEC_Astronomy
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- Contact:
Not to change the topic but I am in need of a tach and I was wondering if Mral and Chris could suggest a good way to get a clean signal. I have plenty of phototransistors and CDs cells, which would be better? Don't phototrans have a quicker response time? I bought several cheap red lasers and so those aren't a problem. I need a circuit that would give me a clean enough signal to trigger a CMOS or TTL chip clock just once with no jitter or bouncing. How easy is that to do? I have two versions in mind. One would be just a microcontroller with a lot of code to properly read the switch and the other idea is to feed the signal into a binary counter and read the output maybe once a millisecond and then divide it by the number of fan blades and then times it by 60000 (Is that right? 1000 milliseconds to one second and 60 seconds to a min so with that math I should get RPM's right?). I know 1 mili refresh rate might be faster than I need but I can adjust that to whatever is practical. Would one version be able to cover the very fast to the very slow or should I plan on making maybe two of these one for 10,000RPM and up devices and one for lower speeds?
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