I just thought of an idea for a circuit where you can have potentiometers = ADCs x Outputs w/a single chip, and still get a reading for each individual pot! So you hook up the wipers of all the pots to one of the three ADCs (for example, w/ 8 outputs, hook up 8 pots to each ADC). Then, you connect one end of every Pot to ground, and then hook up the other end of 3 pots to each output (in a grid, each row's wipers would be connected to one ADC, and each column's ends would be connected to a single output). Then, you switch HIGH on the output for the column you want to read, and get an ADC reading for each pot! You could quickly go through with two nested For loops and store it in a matrix.
Have Tons of Pots!
- Thread starter fizzit
- Start date
AndyGadget
Senior Member
Sorry - It wouldn't work!
You would get all the 'lower' resistances in parallel to ground affecting the reading of the pot you've enabled. One pot at minimum (slider to ground) would ground the whole array.
You would get all the 'lower' resistances in parallel to ground affecting the reading of the pot you've enabled. One pot at minimum (slider to ground) would ground the whole array.
SilentScreamer
Senior Member
Would using tri-state logic and making them all inputs while not reading work?
Andrew Cowan
Senior Member
Depends on the pot resistance.
PIC input impedance is roughly 20K.
A
PIC input impedance is roughly 20K.
A
Diode or them?
We had a board in a theater I worked in that was a programming sequence board (open curtains, dim lights, start projector, etc.) Time was the rows, selected by the clock, function was the columns, selected by a diode. As Best I recall. That was about 30+ years ago.
We had a board in a theater I worked in that was a programming sequence board (open curtains, dim lights, start projector, etc.) Time was the rows, selected by the clock, function was the columns, selected by a diode. As Best I recall. That was about 30+ years ago.
inglewoodpete
Senior Member
Fizzit, Don't give up, the idea is still a good concept Check out the Doc's post. You just need the 4051/2/3 to isolate the pot or bank of pots with a high impedance, that's all.
Can you draw your idea?
I've done a similar thing with multiple LDRs into a single ADC using tri-stating, but I think, assuming my mental image is correct, that you will get an interaction.
But I may have got the picture wrong.
This is why a drawing can save dozens of words .... and save confusion/ambiguity too.
You may find the only accurate solution is one of those analogue multiplex switch things... or get a bigger PICAXE
Yes, you could start adding semis to switch the low side, but then you have the contribuiton made by the semi-junction.
FETs would be better. But the unwanted effect ('resistance', vdrop, tempco etc.) of any switch (including a PIC I/O port) will depend on the values of your pots.
I've done a similar thing with multiple LDRs into a single ADC using tri-stating, but I think, assuming my mental image is correct, that you will get an interaction.
But I may have got the picture wrong.
This is why a drawing can save dozens of words .... and save confusion/ambiguity too.
You may find the only accurate solution is one of those analogue multiplex switch things... or get a bigger PICAXE
Yes, you could start adding semis to switch the low side, but then you have the contribuiton made by the semi-junction.
FETs would be better. But the unwanted effect ('resistance', vdrop, tempco etc.) of any switch (including a PIC I/O port) will depend on the values of your pots.
Last edited: