Author Topic: Multiple sequential inputs into ADC  (Read 577 times)

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Offline OrangeBrickTopic starter

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Multiple sequential inputs into ADC
« on: January 22, 2022, 10:25:50 pm »
Hi all,

Making a transmitter for R/C project, which will have 2x joysticks.
However in using the Pi Pico, this has only 3 accessable ADC inputs.
Therefore I'd like to measure 2x joysticks (each with 2x potentiometers for X/Y axis) and if possible the battery voltage + another potentiometer.

Summing this up:

ADC1 -> Joy-1_X
              Joy-2_X

ADC2 -> Joy-1_Y
              Joy-2_Y

ADC3 -> Voltage from potential divider
              Extra potentiometer

1) Is it possible to use MOSFETs to modulate the input voltage supplied to the potentiometers on these joysticks, such that you'd measure one (powering it, and not the other), then the other. Measuring each Joystick in sequence, Joy1-X on ADC1 and Joy1-Y on ADC2, then Joy2-X on ADC1 and Joy2-Y on ADC2.

2) It follows if above is true that ADC3 should be able to sense voltage and a extra potentiometer, again in sequence.

Right now I'm looking at BSS138 for transistors, operating at 3.3v (or 0v) gate voltage supplied from Pico GPIO, to power on/off potentiometers or allow current from potential divider circuit to flow. From my basic understanding these should be sufficent even at the relatively low gate voltages (3.3v).

I hope this made some sense, and apologies if not, I'm happy to explain more (or try to) if needed! Many thanks.
 

Offline Kim Christensen

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Re: Multiple sequential inputs into ADC
« Reply #1 on: January 22, 2022, 11:55:46 pm »
Typically you would use an analogue multiplexer like the cd74hc4067, 74HC4051, LTC1391, etc. Depends on the voltage range of the signals you want to switch.
 
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Offline OrangeBrickTopic starter

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Re: Multiple sequential inputs into ADC
« Reply #2 on: January 26, 2022, 05:44:17 pm »
Ah didn't know they existed, they look like exactly what I need! Cheers.
 


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