Using VREF pins for pots that don't reach ADC=0 or 255

[Acetronics2]

@ first, I do not see the " magic " decoupling caps that have to be located just close to the µP ...

[richard]

I still don't understand how 15mV at VREF- is not able/sufficient to deal with 1.5mV at the pot...?

15mV pales into insignificance with respect to 0.234 volts of noise

[Demon]

I will add 2 other caps now.

EDIT: 0.1uF, 0.01uF and 0.001uF right at the pin, no difference, ADC stops at 12.

[Demon]

Oh god..... (smacks-face)

I cleaned up the WPU, I think I had one on ADC.

WPUA = %11111010                        ' Pin A2 = Vref-
                                        ' Pin A0 = ADC (B5K)
WPUB = %11111111
WPUC = %00111111                        ' Pin C7 = RX
                                        ' Pin C6 = TX
ANSELA = %00000101                      ' Pin A2 = Vref-
                                        ' Pin A0 = ADC (B5K)
ANSELB = %00000000
ANSELC = %00000000

I just tried again with the batteries and it went down to ADC=0.

Arrrgggghhhhh.......

[Demon]

I've removed all caps, and this pot works perfect. The TPS56637 circuit is that clean when it comes to noise.

WPU was fighting with the ADCin pin, trying to pull it up.

Now the slider pots might still be a problem; I'll test those later. But right now I'm putting back the 2nd pot with switch.




I'll probably put several of those caps back on, I'll see (like at ADCin pin).

Unfreakingreal... :bangheadinwall:


EDIT: Oh yeah, definitely had to put the caps back on. The 2nd ADCin started affecting the 1st.

I put all the caps back in, everything is stable.

[richard]

I cleaned up the WPU, I think I had one on ADC.

more proof that blindly setting pin registers is bad practice and serves no purpose .
the safe setting is to leave them as default unless you need them to be different

if you use mcc its perfectly clear how each pin is set and self documenting

[Demon]

I'm still using MCS+.

Can we use MCC standalone? Or do we have to "create a project" and do the entire process within MPLAB?

I have both the MeLabs USB programmer and PK4. I suppose I could set up an older PC with MCS+ and Melabs pgmer, and use PK4 with MPLAB on this more powerful PC.

[Ioannis]

Yes you can install a stand alone application. No need to have the complete IDE.

https://ww1.microchip.com/downloads/....1-windows.exe

Ioannis

[richard]

Or do we have to "create a project" and do the entire process within MPLAB?

mcc stand alone is ok it works for all the chips i typically use. i don't know if they keep it UpToDate.
the latest mcc with mplabx6 is wildly different and i don't like the look of it so i don't use it


creating a project takes 2 or 3 minutes tops , its excellent for setting any and all modules including the osc not just the pins
you are only interested in the mcc generated files , they translate into pbp fairly easily with a bit of practice. the project has no other role other than documentation.

it matters not between mcc standalone and mplabx5.xx the effort and time are virtually identical

[Ioannis]

There is a much simpler tool under GCB (Great Cow Basic project) called PPS Tool. It is used for setting the PPS registers with ease.

This free compiler has great potential and good support (forum and YouTube videos).

In general it is easier to setup a PIC with GCB than PBP. Have not used it much to have a detailed opinion.

Ioannis