Potentiometers

[Ronald]

I'm kind of newie in PIC. Do you guys think if it's possible to use some Pic as a digital Potentiometer. I would like to control the value of a Resistor of a range from 20k to 150k. Can I do that with PIc?
Thank You.

[PCM programmer]

My advice is to buy one. They're cheap.

Go to Digikey and type in the search box: Digital Pot
http://www.digikey.com/
Then when you get the next page, select the tickbox for Items in Stock
and click Search Again.

It lists 749 of them.

[rnielsen]

A PIC can take an analog signal and turn it into a digital value so it can process it but I would recommend not trying to create an analog value with a PIC. Like PCM stated, it would be better to use a digital POT to generate your analog signal. There are many available that interface in various ways to the PIC, ie. I2C, SPI, Parallel.... They come in many different values with different resolutions.

Ronald

[ROnald]

Thanks, I found the digital potenciometer MPC41010.
I did a code to use it. But it didn't work. I can compile , but when I tested it at Proteus nothing happend. I debugged and It's Like never left the second line , it didn't "enter"at the main program.
Could guys Help me please to find where It's wrong. I can't find. I connected pin bo to SI( MPC41010) , pin b1 to SCk and pin b2 to CS.
Thanks for the heelp.
Here's the code:

#include <16f877.h>
#Use delay(clock=4000000)
#fuses NOWDT , XT , PUT ,NOPROTECT , NOBROWNOUT , NOLVP , NOCPD ,NOWRT, NODEBUG

#define spi_clk pin_b1
#define spi_dta pin_b0
#define spi_cs pin_b2

void spi_write_bit (boolean bit);
void spi_write_byte(byte data);

void main (void)
{
int data;
set_tris_b(0);
delay_ms(10);
while(1)
{
data=10;
spi_write_byte(data);
delay_ms(15000);

}


}

void spi_write_bit (boolean bit)
{
output_bit(spi_dta,bit);
output_high(spi_clk);
delay_us(1);
output_low(spi_clk);
}
void spi_write_byte(byte dado)

{
int conta=8;
while (conta)
{
spi_write_bit((shift_left(&dado,1,0)));
conta--;
}

output_float(spi_dta);

}

[PCM programmer]

[Ronald]

Have someone ever use MCP41010 with PIC16f877? I use the code from c:\program files\picc\drivers\mcp41010.c , and this simple main fuction:

void main (void)
{
int data;

delay_ms(10);


data=100;
set_pot(data);
while(1);


}

And I test a simple voltage divisor , I conected pin PAO to a Power , Pin PWO to a resistor that it's connected to ground , and PBO to ground. And I checked the voltage between the PWO and the resistor . It's Stay all the same even when I change the data value. Please Help Me.
Thank you so much for your Help

[PCM programmer]

In your original code you have these settings:

[Ronald]

I used:
#define CS PIN_B4
#define SCLK PIN_B2
#define SI PIN_B1

And connected right to the Pot, but nothing happended. Have someone ever simulate that?

[Ronald]

I found what's wrong . I should have put shutdown_pot (); before using the digital pot.

[Ronald]

Have someone ever simulate or use the Dig Pot MCP41010? I'm using the ccs library for using it , the functions void set_pot (int data) and void shutdown_pot (). When I want to set the Pot just one time it works , like:

int data;
shutdown_pot ();
delay_ms(10);

data=220;
set_pot(data);

but , if I try to set the value 2 times like


int data;
shutdown_pot ();
delay_ms(10);

data=220;
set_pot(data);
delay_ms(5000);
shutdown_pot ();
delay_ms(10);

data=220;
set_pot(data);

It only set the first time , it doesn't change the value . I don't know if it's a Proteus problem , that the only component that can change with time it's the simple Pot or if it's something with the code. Have someone ever used that?

[Ronald]

Please , somebody help me!

[PCM programmer]

This is not a Proteus board. Get some real hardware and we can
probably do something.

[Ronald]

What you mean by real hardware ?Sorry I'm start learning about one month ago.

[PCM programmer]

In an earlier post you said this:

[rberek]

I tested the MCP41010 model in Proteus and confirmed the behaviour you described.

I contacted Labcenter and they also confirmed that it was a bug in the model and have fixed it. If you check out the "Bug Reports" section of their forum you will see the new files have been posted. I tested the new model and it works.

Note that if you aren't a registered user, you will not see this section of the forum. Just like CCS code, I can't pass that code to you, so you will have to obtain it from the company yourself.

A good catch on your part.

Rod