12F683 - basic code not working

[Scampy]

Following suggestions I've ordered a module from e-bay based on an L298N controller, which should work as under testing the 540 motor was drawing 0.7A and these things are rated at 2A.

I'm now working on the light detection side of the circuit. Basically the idea is to automatically open a door at dawn (wife now keeps chickens !). So when the light level reaches or exceeds a threshold, the motor runs, opening the door until the door hits a micro switch which then changes a pin status which then turns off the motor.

I've purchased a 16k-33K LDR from Maplin ( http://www.maplin.co.uk/p/16k-33k-oh...resistor-n57ay ) and connected that from the 5v line to GPIO.0 and covering the LDR makes the associated LED on my development board go out, and increase in brightness due to ambient light or when a bright torch is shon on the LDR. So the resistance is varying based on the light level, so far so good. Now the issue I'm having is that having set the ACD to 8 bits this should give me a 0 - 254 range of values... but in testing to get the motor to run at various values, these are not what I would expect.

Here's the test code:

ASM
 __CONFIG _INTRC_OSC_NOCLKOUT & _WDT_ON & _PWRTE_ON & _MCLRE_OFF 
endasm

' Hardware configuration
' ======================



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

Motor1 var GPIO.4
Motor2 var GPIO.5
ADChannel0 var word

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

main:
low Motor1
low Motor2
adcin 0,adchannel0 ' Read AN0

If adchannel0 >2 then
  high Motor1
  Low Motor2
  pause 5000
low Motor1
low Motor2
endif

goto main

If I put in <1 for the argument, the motor runs even with the LDR covered. If I put in >1 the motor won't run unless I shine the torch directly on the LDR. I'm sitting here in ambient light with the sun shining in the window so the motor should be running.

Any ideas as to what I'm doing wrong ?

[Demon]

Do you use a word for 8 bit as well?

Motor2 is never going on by the way.

Robert

[Scampy]

OK corrected that (original example code must of been for higher resolution...) but still no joy in setting the thresholds

Motor two is always off in this example as its the other terminal to the H bridge

[aratti]

You should post the schematic of your project in order to get proper help. Very likely your problem is in the hardware arrangement.

Cheers

Al.

[Scampy]

Al,

The PIC is on an EasyPIC5 development board, but basically this is the schematic. I've also tried replacing the LDR with a 10k pot and whilst the LED on the dev board dims in brightness the threshold values still have the same effect. Placing the LDR between +5 and GPIO.0 gives a better range of brightness in the LED (not shown in the schematic) from off when the LDR is covered, to bright when an LED torch is placed directly over the LDR.

I don't program much, so often feel like a newbie when I dust off the development board, and ADC is something I've only once played with. As far as I can understand, the voltage on GPIO.0 should be converted into a byte value between 0 and 254, so I could set the threshold at which point GPIO.4 is made high ?

[Demon]

Shouldn't there be protective diodes "somewhere" whenever a motor is used?

I don't really get how that motor is wired. I would expect a pulse method, but the code is constant on for 5 seconds.

Admittedly confused.

Robert

[Scampy]

Robert,

I grabbed the h-bridge circuit from a web site, which using pnp / npn transistors works ok for the test motor (see above). I will be using an H-bridge chip for the larger motor.

Yes for testing I have the motor running for 5 sec once the threshold has been breached