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    two ADCs; two uC; one pot

    Hi,

    I want to drive two ADCs from one pot. The ADCs are in microcontrollers in separate enclosures. But i guess there is an issue tying the rails together. How can that be done?
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    Re: two ADCs; two uC; one pot

    Provided the two 5V regulators are happy to cooperate, I don't see anything wrong with doing that, even if it is an unusual task. All you have to be careful of is the positive reference voltage to the ADC, if both are the same or VDD it should work but beware of problems if you use a lower reference than the voltage coming off the pot.
    It might be a good idea to add resistor (~470 Ohms) at each ADC input just in case the sampling time of one pulls the voltage down at the other but that would only really happen if the pot value was too high.

    Brian.
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    Power supplies in parallel

    what happens on the wiper when two power supplies are put in parallel across a pot.

    The scenario is two guitar effects units each with an expression jack. The jack outputs 5volts and is supposed to go across a potentiometer and the wiper voltage is fed back to the effects unit.

    Assuming one potentiometer controlling two effects units the power supplies would be in parallel.
    I have built a simulation circuit and things seem to work ok, and I guess I can actually build the circuit and see what happens.

    but, what do you think would happen?



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    Re: two ADCs; two uC; one pot

    Hi,

    what happens on the wiper when two power supplies are put in parallel across a pot.
    The wiper will have no problem, it just sees the voltage, but can't know if there is one or multiple sources.

    As already mentioned: You need to ensure that the power supplies can withstand this situation.

    I recommend not to directly connect the two supply outputs. One supply for the pot is sufficient.
    Another option is to use two diodes to supply the pot from two different supplies. Maybe a BAT54C...

    Klaus
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    Re: two ADCs; two uC; one pot

    don't know why this has been moved. Situation is different. The previous circuits were one's I had designed that had nothing more in them than a direct connection to an A/D input and direct connections to the rail.

    I don't know what is inside the effects units exactly. Though I have a schematic for one of them here


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    Re: two ADCs; two uC; one pot

    How can i do this?

    I want a simple expression pedal splitter where one expression pedal can be used to control two effects units.

    However, one effects unit uses 5volts and the other uses 3.3volts. I thought some Schottkey clipping diodes like in the schematic would do the trick, but it seems to be clipping at about 4 volts rather than 3.3v. Why would that be?

    The 27K resistor is needed because this particular 3.3volt effect unit will not modulate with a simple varying supply on the tip of the control jack, but must also have a small load as would be expected if an expression pedal was connected to it. Most effects are not like that, but this one is.

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    Re: two ADCs; two uC; one pot

    However, one effects unit uses 5volts and the other uses 3.3volts.
    How comes that you give new specifications every time (have been talking about 5V only in post #3)?

    As a generally consideration, you surely don't want to clamp 5V output to 3.3V without reasonable current limiting resistor.



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    Re: two ADCs; two uC; one pot

    Quote Originally Posted by FvM View Post
    How comes that you give new specifications every time (have been talking about 5V only in post #3)?

    As a generally consideration, you surely don't want to clamp 5V output to 3.3V without reasonable current limiting resistor.
    why the change? because Klaus the forum administrator, in his infinite wisdom, issued a warning and combined the posts.

    don't want to clamp 5v to 3.3. why not?



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    Re: two ADCs; two uC; one pot

    Don't blame others for nor clearly explaining your circuit.

    Anyhow, your latest schematic is shorting 5V to 3.3V through a diode in C.W. position. This can e.g. lift the 3.3V supply and cause circuit failure.



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    Re: two ADCs; two uC; one pot

    Hi,

    Please review your posts.

    I´ve merged both threads, because you didn´t respond to the first thread but started a new thread with a similar problem.
    Both your posts discuss a problem of tying two supply rails together. Both your threads talk about 5V only.
    --> similar problem.

    Your information about different supply voltage obviously came after I have merged both your threads.
    Merged thread or not... your information in post#6 is new information.

    ****
    Regarding your problem:
    I assume the 5V ADC expects an input voltage of 0...5V from the pot (wiper). If you clamp the pot supply voltage to 3.3V, then obviously the 5V ADC can only see 0..3.3V.
    Thus it´s input signal is limited to 0..66%. I assume this will cause problems.

    There´s a lot of information missing, thus we have to guess a lot.
    I assume the two effect devices do not work at the same time, they work alternating.. if so then an alternating switch could be used to select the effect device.

    Klaus
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    Re: two ADCs; two uC; one pot

    clamping 5volts to 3.3 is ok. Just trying to stop a blow up rather than incorrect functioning.

    Yes both effects will be working at the same time. that's the point of the circuit.

    A user might use two 3.3volt units, two 5 volts units, or a 3.3 and 5 volt in any order.



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    Re: two ADCs; two uC; one pot

    Hi,

    Is there a way to modify the pedal and install a dual/stereo pot or two pots?
    This could solve all electrical problems.

    Klaus
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    Re: two ADCs; two uC; one pot

    This would be a commercial product, a simple expression pedal splitter and so no modifying a pedal is not an option



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