12F683 - basic code not working

[aratti]

Check the risistence of your LDR in both condition (dark and light). Since the lowest resistance should be found in light, use this value for your devider network. In this way you should have a value in volts near to zero in dark and near to Vdd/2 in light, more than enough to be sure to trip the system at the right time.

By the way the schematics of your Hbridge is wrong! NPN should be connected on the low side, while PNP should be connected on the high side.

Follow the wise suggestion given above, always use freewheel diodes when using inductors!

Cheers

Al.

[Scampy]

Al,

My fault, I drew the schematic the wrong way round (I was rushing ). I've now placed diodes between the collector and emitters of each transistor as suggested.

Measuring the LDR I get a few hundred ohms when the torch is directly into the face of the LDR and around 2.1m ohms when I place my finger over it. Under the ambient light in the room it was averaging 16K - 18K. I've tried placing the LDR and an 18k resistor in series between +ve and GND and then connecting GPOI.0 to the junction between the two. The LED on the development board was lit quite bright and covering the LDR had no effect. I then used a 200 ohm resistor based on the fact that in light the resistance was a few hundred ohms when tested.

With the 200 ohm resistor in place as a voltage divider with the LDR, under normal room light with a value of adchannel0 >2 in the if then statement the motor runs. If I change that to adchannel0 >3 and re-compile the motor won't run regardless of bright light or darkness.

With the divider made up as the LDR between +5v and GPOI.0, and the 18K between GPIO.0 and GND I get 0.6v on GPIO.0 when the ldr is covered, and around 3.5v with the torch shone directly at the ldr. So I would assume this voltage range of 3v should be enough for the ADC to read ? so why is it that the ADC is acting more like a switch with a value of 1 rather than 255 steps ?

[aratti]

Add the following defines on top of your code:

DEFINE ADC_BITS 8
DEFINE ADC_CLOCK 2
DEFINE ADC_SAMPLEUS 50

Cheers

Al.

[Scampy]

Hi Al,

I've modded the code so I can see what's going on.

ASM
 __CONFIG _INTRC_OSC_NOCLKOUT & _WDT_ON & _PWRTE_ON & _MCLRE_OFF 
endasm

TRISIO = %001111 
ADCON0 = %10000001 
ANSEL = %00110011 
DEFINE ADC_BITS 8
DEFINE ADC_SAMPLEUS 50 
DEFINE ADC_CLOCK 2
CMCON0=7


Tx              var GPIO.5         
ADChannel0 var byte

GPIO = 0 ' clear all output
Pause 50 ' internal oscillator settle time

main:
adcin 0,adchannel0 ' Read AN0
Serout2 Tx,84, ["val: ",#adchannel0,10]
pause 5000

goto main

The divider made up as the LDR between +5v and GPOI.0, and the 18K between GPIO.0 and GND.

Compiled the code and loaded it to the chip. Opening the serial tool in Micro-studio I get a value of 1 when the LRD is in ambient light or covered and 2 with the torch shone directly on it.

Ideas ??

[Scampy]

As a postscript, i wired a 10K pot between +5v and GND with the wiper to GPIO.0 and got the same results - seems the ADC isn't working

[Scampy]

OK I'm going to throw this thing out the window in a moment

I downloaded a sample code from this forum written by Bruce

ASM
 __CONFIG _INTRC_OSC_NOCLKOUT & _WDT_ON & _PWRTE_ON & _MCLRE_OFF 
endasm

DEFINE ADC_BITS 10
DEFINE ADC_CLOCK 3
DEFINE ADC_SAMPLEUS 50
number VAR word

'CMCON = 7 ' Comparators off
ANSEL = %00000001 ' GPIO.0 A/D in, rest digital
ADCON0.7 = 1 ' Right justify for 10-bit
GPIO = %00000000 ' Initialize outputs
TRISIO = %00000001 ' GPIO.0 = input, rest outputs
Tx              var GPIO.5


main:
adcin 0,number ' Read AN0
Serout2 Tx,84, ["val: ",#number,10]
pause 5000
goto main

With the 10K pot wired between the supply with the wiper to GPIO.0 and get readings between 437 and 440 !!!!!!!!!!!!!! - still just three digits between min and max.
I had to rem out the CMCON line - presumably the 12F683 has no comparators, would that be the case.

[Archangel]

Hi Malcolm,
Comparator register for this chip is CMCON0 set CMCON0=7 to turn off as per data sheet 8.3
It compiles. You might have to set the CCP1CON to zero too , not sure about that though.

[HenrikOlsson]

Hi,
I haven't been following this thread but why do you say presumably the 12F683 has no comparators, would that be the case ?

Why not simply open the datasheet and have a look? Sure enough, the 12F683 DOES have a comparator and it's control register is CMCON0 - which you had got correct in your previous snippets of code but not in the latest one. I'm not saying this is the problem though.

Verify that ALL your grounds/commons are connected, as you move the wiper of the pot measure the voltage right at the PIC, between pins 8 (Vss) and 7 (AN0) to verify that it's not a loose connection or floating ground etc.

/Henrik.