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djsb
Joined: 29 Jan 2011
Posts: 49
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| ADC Channel selection/switching on PIC16F1847 |
 Posted: Thu Mar 13, 2025 10:29 am |
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I can't seem to change the channel on my PIC16F1847 using this code snippet
| Code: |
setup_oscillator(OSC_8MHZ); //Set clock speed
setup_vref(VREF_OFF); // 1v024,2v048,4v096 available. Using 2V as max output of MCP9700A is 1.75 Volts. Experiment to observe effects of changing the reference voltage. Try LSB_TWO_V first.
setup_adc(ADC_CLOCK_INTERNAL);
//setup_adc_ports(sAN2,VSS_VDD);
//set_adc_channel(ALL_ANALOG);
setup_adc_ports(sAN0,VSS_VDD); // Configure AN0 pin as analog
set_adc_channel(sAN0);
delay_us(10);
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I'm also using I2C channel 1 on port B, but this works OK. I've managed to get a 10 bit resolution ADC reading displayed on the I2C LCD screen but can't change the ADC channel to anything BUT AN0.
It won't use anything apart from AN0 no matter what I change the code to.
What is the CORRECT way of setting up a specific ADC channel on this chip. And how would ADC channel switching be done properly?
The hex file is being updated when compiled, and I'm using PCM V5.110 on Windows 10. Is there some kind of pin configuration procedure I'm missing? Thanks. |
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Ttelmah
Joined: 11 Mar 2010
Posts: 19765
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| Posted: Thu Mar 13, 2025 11:13 am |
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Stepping through your code:
| Code: |
///setup_oscillator(OSC_8MHZ); //Set clock speed
//Get rid of this. Just use INTERNAL=8MHz in the #use_delay setup
setup_vref(VREF_OFF); // 1v024,2v048,4v096 available. Using 2V as max output of MCP9700A is 1.75 Volts. Experiment to observe effects of changing the reference voltage. Try LSB_TWO_V first.
setup_adc(ADC_CLOCK_DIV_8);
//Generally do not use the internal oscillator for best accuracy.
//Your chip is a late enough one that it does not warn about this in
//the data sheet, but iit is still better to use a clock that is synchronised
//to the master oscillator. This will also give faster conversion.
setup_adc_ports(sAN0 | sAN1,VSS_VDD); //Configure AN0 and AN1 as analog
set_adc_channel(0); //Do not use the s defines here, just the channel
//number
delay_us(5); //only 5uSec needed on this chip.
val0=read_adc(); //this will now be AN0
set_adc_channel(1); //Select channel 1
delay_us(5);
val1=read_adc(); //this will now be AN1
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Key problem is that all analog channels you need to use need to be
connecter to the multiplexer, This is done by 'or'ing them into the port
setup. Then you only use a channel number, to say which channel to
read, not the sANx define. You need VREF_ADC_2v048 in the Vref setup,
and VSS_FVR in the adc setup to use 2.048v. Note that this is the
minimum internal Vref that the ADC can use. It requires 1.8v minimum
to give it';s specified accuracy. The internal reference is only about +/-7%
accurate. For 10bit you really need a much better Vref than this. |
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djsb
Joined: 29 Jan 2011
Posts: 49
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| Posted: Sat Mar 15, 2025 10:47 am |
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Thanks  |
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