set_analog_pins() in a loop

salihonur · Joined: 21 Mar 2020 Posts: 22

Hi

How can I set analog pins in a for loop with if statements using set_analog_pins() function? Each IOs which are defined in a array (for example look at below) will be set according to IO type.

I mean my IO's are configurable by the technician. He will set IO type parameters according to the hardware design. He will not re-compile and upload the firmware into the MCU. Just he sets by parameters. IOs can be mixed analog inputs. (Except C and D port pins)

I see that the set_analog_pins() requires multiple pins at once to set as analog input.

My pin define (PIC18F46K80):

Ttelmah · Joined: 11 Mar 2010 Posts: 19506

Your technician needs to be very careful doing this. The problems are that
if you have a pin set as 'analog', and feed a digital signal into it, this will
result in significant cross-talk to the analog signals. Then if you have a pin
set as 'digital' and feed an analog signal into it, this can result in
excessive current consumption, and even overheating of the input stage.
It is possible, but many of the pins you show don't support analog
operation.

temtronic · Posted: Wed Dec 02, 2020 5:54 am

As Mr.T points out, while it could be made to work, there's a huge hardware problem.
Normally any analog signal to the PIC has to be 'conditioned'. This could be anything from a 'simple' R-C filter to an opamp with offset and level shifting. Even 'simple' R-C filtering needs to be designed for the actual signal that is being sampled. While getting a PIC ADC to reliably run in 8bit is 'easy', sampling at 10 or 12 bits does require a LOT of design to get components values correct, perfect PCB layout,rockstable Vref,lots of proper bypass caps and perfect wiring.
While having the ability to 'field alter' the function of a pin may look good on paper, there's hundreds of 'details' that must be worked out AND tested.
I'm not saying it can't be done, but perhaps a reconfigurable colour coded cabling system, might be an option ? Using a red cable, means the tech enters '2' as the configuration, grn cable = '5'.
hmm.. whatever config is selected, be sure that data is stored in EEPROM ! ,so when PIC reboots, say from power failure, the correct config is used.

Jay

salihonur · Joined: 21 Mar 2020 Posts: 22

Thanks very much for your warning. Analog input doesn't go to the MCU directly. I designed the power board as modular. So each IO type has own module. And also analog input module has a opamp circuit and filter components.

setup_adc_ports with int32 is good solution. Thanks a lot.
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