I have added a mototized stereo pot to my B1 buffer, allowing me to adjust the volume using an IR remote. It is working brilliantly.
I would now like to monitor the output resistance of the pot in order to (a) add a volume level display, since the B1 will be tucked away in a cabinet, (b) stop the motor if it reaches the end of the pot’s travel. Currently, if the user keeps holding the vol up/dn button, the motor keeps trying to turn the pot and I’m worried about damaging the motor. Finally (c), I like the idea of having a preset volume level, e.g. for night listening. I would like to instruct the motor to move the pot until it reaches the preset volume level. I know its silly but I’d find it a really useful feature!!
Can anyone advise how I might monitor the output resistance of the pot without degrading the audio signal? I would like to feed the monitor signal to a microcontroller e.g. Arduino. I’m worried that even a tiny voltage inserted into the audio signal will be detrimental.
If there isn’t anway to do this then I guess I could try to find a 3 or 4 channel motorized pot and monitor the resistance using a spare channel. Unfortunatly I’m on a tight budget and won’t be able to replace this with such a nice pot.
Thanks!
I would now like to monitor the output resistance of the pot in order to (a) add a volume level display, since the B1 will be tucked away in a cabinet, (b) stop the motor if it reaches the end of the pot’s travel. Currently, if the user keeps holding the vol up/dn button, the motor keeps trying to turn the pot and I’m worried about damaging the motor. Finally (c), I like the idea of having a preset volume level, e.g. for night listening. I would like to instruct the motor to move the pot until it reaches the preset volume level. I know its silly but I’d find it a really useful feature!!
Can anyone advise how I might monitor the output resistance of the pot without degrading the audio signal? I would like to feed the monitor signal to a microcontroller e.g. Arduino. I’m worried that even a tiny voltage inserted into the audio signal will be detrimental.
If there isn’t anway to do this then I guess I could try to find a 3 or 4 channel motorized pot and monitor the resistance using a spare channel. Unfortunatly I’m on a tight budget and won’t be able to replace this with such a nice pot.
Thanks!
Thanks for your reply. I don't have a schematic as the volume board was scavenged from an old sony preamp. I'm not sure of the model.
It is quite simple though. The motor is driven by a ba6208.
The pot is completely isolated from the motor.
Thats all there is to it, but I'll try to sketch it up for clarity.
It is quite simple though. The motor is driven by a ba6208.
The pot is completely isolated from the motor.
Thats all there is to it, but I'll try to sketch it up for clarity.
I have made a schematic of the motor board. The 2x10k potentiometer replaces P100 and P200 in the B1 circuit.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
Gbuilder.
Your vol pot wiring is missing some connections.
The input is two channel. Therefore you need 4 wires to connect the 2 channels of input signal.
The output is two channel, therefore you need 4 wires to connect the 2 channels to the next stage.
Do not take any signal wires to some remote ground, which will lead to more pickup of interference.
Your vol pot wiring is missing some connections.
The input is two channel. Therefore you need 4 wires to connect the 2 channels of input signal.
The output is two channel, therefore you need 4 wires to connect the 2 channels to the next stage.
Do not take any signal wires to some remote ground, which will lead to more pickup of interference.
These motorized pots are usually built with some slip so that the motor driver is not damaged. (BTW, heatsinking on these is not always adequate and may appreciate being beefed up.)
Figuring out the position of the pot is not impossible but not easy. I would generate an ultrasonic signal, run that into the pot via a tuned series LC, extract it on the other side at narrow bandwidth (or at least lots of highpass to keep the audio signal off) while keeping it out of the amp using a parallel LC in series and series LC to ground, then run it into a sufficiently fast precision rectifier followed by a logarithmic amp. This would have to be calibrated for amplitude and slope, once when setting up the amp and then maybe once in a while, depending on how drifty your LCs are (hint: no ceramics other than NP0). One could use a DC measurement as a reference then.
Figuring out the position of the pot is not impossible but not easy. I would generate an ultrasonic signal, run that into the pot via a tuned series LC, extract it on the other side at narrow bandwidth (or at least lots of highpass to keep the audio signal off) while keeping it out of the amp using a parallel LC in series and series LC to ground, then run it into a sufficiently fast precision rectifier followed by a logarithmic amp. This would have to be calibrated for amplitude and slope, once when setting up the amp and then maybe once in a while, depending on how drifty your LCs are (hint: no ceramics other than NP0). One could use a DC measurement as a reference then.
Thank-you, a mechanical approach is quite appealing since I can completely avoid messing with the audio signal. You are right that the motor is geared. I think it will have the torque, although it will be a bit fiddly to construct the pulley mechanism. I'll try to take a picture later.
That leads me to wonder if there is such a thing as a shaftless or hollow-shaft potentiometer, which I could fit over the shaft of my volume pot. That would certainly be mechanically easier. From a quick search, they don't seem common, although there are a lot of rotary encoders which work this way. Another option is a sliding pot (like amixing desk fader), driven by a gear on the volume pot shaft.
Thank-you very much for the imaginative suggestions!
That leads me to wonder if there is such a thing as a shaftless or hollow-shaft potentiometer, which I could fit over the shaft of my volume pot. That would certainly be mechanically easier. From a quick search, they don't seem common, although there are a lot of rotary encoders which work this way. Another option is a sliding pot (like amixing desk fader), driven by a gear on the volume pot shaft.
Thank-you very much for the imaginative suggestions!
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May be you can use motorized 4-deck ALPS RK27 potentiometer. The pot will fit any standard controller board but will stick a bit forward. Use one of the first two decks for position monitoring. For convenience you can even change one deck to linear taper (from the other dual/single ALPS RK27 pot) and use it to monitor the angle...
Another idea is to measure the level of the signal going into the pot and the level of the signal coming out of the pot and determine the attenuation directly and accurately. The THAT RMS detectors (inside of their Analog Engines - 4301, 4305, 4316) can do this easily, and provide a dB/V output making the math very easy - the gain in dB is just the difference in the two RMS detector outputs.
The one bug with this is that the accuracy could be really poor when the input to the pot is low, but some clever logic (perhaps to only sample the setting when the signal is sufficiently large) might be able to make up for that.
The one bug with this is that the accuracy could be really poor when the input to the pot is low, but some clever logic (perhaps to only sample the setting when the signal is sufficiently large) might be able to make up for that.
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