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Nora
Joined: 23 Mar 2008
Posts: 50
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| ADC Port E with 18F452 |
 Posted: Mon Dec 01, 2008 5:51 am |
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Hello-
I have a temperature sensor connected to an op-Amp (Gain of 10) then connected to a PIC 18F452 Pin 9, AN6, also defined as RE1 and WR.
I am using the PICDEM 2 PLUS, ROHS version. According to the schematic, nothing else seems to be connected to this pin.
http://ww1.microchip.com/downloads/en/DeviceDoc/PICDEM%202%20Plus%20RoHS.pdf
When I measure the voltage at Pin 9, it will not go higher than 0.9V, no matter what the mV signal is at the temperature sensor. For example, with a mV reading of 0.202, I would expect a V reading at the ADC pin of ~2.02V.
I believe my hardware is correct, as when I change the AC pin to any Port A Analog pin, the reading works as expected. To make my system work, I am now using AN4.
I have an LED on AN7. Could this have been loading down my AN6?
Here's a code snip:
| Code: |
//*****************************************************************
#include <18F452.H>
#device adc=10
#fuses HS,NOWDT,NOPROTECT, PUT, BROWNOUT, NOLVP
#use delay(clock=20000000)
//*****************************************************************
long int ch6_result, temp_cel;
long int temp;
void main()
{
setup_adc_ports(ALL_ANALOG); // All analog and +ref is VDD, -ref is VSS
set_adc_channel(4); // channel 6 active
delay_us(25); // recommendation is to delay
setup_adc(ADC_CLOCK_DIV_32); // from PIC data sheet
setpoint = 93;
while(1)
{
ch6_result=read_adc(); // read ADC
output_high(PIN_E2); // blue LED on
delay_ms(300);
output_low(PIN_E2); // blue LED off
delay_ms(300);
}
} |
Thanks in advance!
N_N |
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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| Posted: Mon Dec 01, 2008 2:13 pm |
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I don't have the Rohs version of that board. I have the previous version.
I modified your program by adding a #use rs232() statement and a
printf(), to show the results of reading the ADC. I changed the ADC
channel to 6, so it would actually test your problem. I added a declaration
for 'setpoint' which was missing. I used PCH vs. 4.083 for this test.
On the board, I jumpered pin A0 to pin E1. This puts the 5K trimpot
on the AN6 pin. I also jumpered pin E2 to pin B0, to provide an LED
on that pin.
Then it worked. As I turned the trimpot through its range, I got this:
| Quote: | 0
0
53
91
230
376
443
590
684
792
1023
1023
1023 |
Here is the modified program:
| Code: | #include <18F452.H>
#device adc=10
#fuses HS,NOWDT,NOPROTECT, PUT, BROWNOUT, NOLVP
#use delay(clock=20000000)
#use rs232(baud=9600, xmit=PIN_C6, rcv=PIN_C7, ERRORS)
//*****************************************************************
long int ch6_result, temp_cel;
long int temp;
int setpoint;
void main()
{
setup_adc_ports(ALL_ANALOG);
set_adc_channel(6);
delay_us(25);
setup_adc(ADC_CLOCK_DIV_32);
setpoint = 93;
while(1)
{
ch6_result=read_adc();
printf("%lu\n\r", ch6_result);
output_high(PIN_E2);
delay_ms(300);
output_low(PIN_E2);
delay_ms(300);
}
} |
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Guest
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| Posted: Mon Dec 01, 2008 2:23 pm |
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Interesting!
Thanks for taking the time to check it out.
I'll look at this again later tonight.
~N_N |
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Nora
Joined: 23 Mar 2008
Posts: 50
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| Posted: Tue Dec 02, 2008 8:04 pm |
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I put the pin back on AN6 with my same result as before.
I tried your code and it worked fine.
OK- must be my code. I hadn't posted my entire code here....
I finally got it working, by commenting out
//set_tris_e(0b01000000); // set all PORTE output, input, rest output
No matter how I set the tris, outs and ins order, I got flaky voltage readings.
Thanks for the help! 
N_N |
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