Just a quickie - when I build this circuit - am I still limited to 10k Pots, or can i use larger value pots as the inputs will be buffered through this module?
Only reason I ask is that there are a few 100K pots in my box.
The pots in my board are 2.2K, if you wanted to add pots at the input to the opamp, you would need to alter the input impedance, or replace the attenuator entirely by the pot.
Just a quickie - when I build this circuit - am I still limited to 10k Pots, or can i use larger value pots as the inputs will be buffered through this module?
Only reason I ask is that there are a few 100K pots in my box.
hi,
I dont want to cut across the info that Nigel's posting, but could you give details of the voltage range you expect from the source and what is the source of the voltage you want to convert.
hi,
I dont want to cut across the info that Nigel's posting, but could you give details of the voltage range you expect from the source and what is the source of the voltage you want to convert.
sry im confused, i dont understand what your asking.
I dont mind what voltage i have to use, whatever is easiest.
I use the internal 5V reference at the moment, but i have been told that using an external reference would improve accuracy.
The way I have it working just now is that pin 'A' of all my pots are connected to +5v, pin 'B' of all the pots are connected to gnd, and each wiper is connected to a different ADC on the pic
sry im confused, i dont understand what your asking.
I dont mind what voltage i have to use, whatever is easiest.
I use the internal 5V reference at the moment, but i have been told that using an external reference would improve accuracy.
The way I have it working just now is that pin 'A' of all my pots are connected to +5v, pin 'B' of all the pots are connected to gnd, and each wiper is connected to a different ADC on the pic
hi,
As the 100K pots are all connected across +5V and 0V, with the pot wiper as output, all you need for each input is a non inverting buffer OPA, between the wiper and the PIC's adc input.
This will accept the high 100K impedance and transform it down close to zero.
For cost I would just buy some 10K pots, no buffers required.
sry im confused, i dont understand what your asking.
I dont mind what voltage i have to use, whatever is easiest.
I use the internal 5V reference at the moment, but i have been told that using an external reference would improve accuracy.
The way I have it working just now is that pin 'A' of all my pots are connected to +5v, pin 'B' of all the pots are connected to gnd, and each wiper is connected to a different ADC on the pic
Makes no difference for that use - you're comparing like with like, if the 5V changes slightly, the reference changes as well - so no point in an external reference.
But what's the point of just hanging 14 pots on the 5V line?.
Makes no difference for that use - you're comparing like with like, if the 5V changes slightly, the reference changes as well - so no point in an external reference.
But what's the point of just hanging 14 pots on the 5V line?.
the pots are connected to various levers, gears, plus few of them are linear pots measuring travel.
I need to log all the information, but from what you have stated above, what I have just now will work fine, I was told the external reference would be more stable, therefore the measurements would be more accurate, guess that i never explained my problem very well.
Thanks to everyone who has helped me, I have to admit that im very digital - i really struggle with analog stuff.
Eric, even if I do buy 10K pots, its still very handy knowing how to connect larger value pots to the pic.
You could do this without needing any analogue inputs on the PIC at all, check my Joystick tutorial, which works in the same way as a PC Joystick port, using a digital input to measure the position of a pot.