Pic12f683 Cmcon0 = 7

[StoneColdFuzzy]

Dave - What is your definition of 'erratic'?

width = mon*1

Oh... Can you tell me what is the point of the *1 part of this line?

Basically your program states that if mon is >2 then your HPWM will be at around 12.5% otherwise it will be solid ON. There's not much else that happens... or at least it would do if you remembered a GOTO MAIN after the last IF statement!!! Because as it is, your code is slamming straight into the OneP section.

You could rewrite your code as...

Main:
    ADCIN 3, mon ' Read channel AN3 to Mon
    width = mon
    if width > 2 then 
	hpwm 1,32,2000
	else
	hpwm 1,255,2000
	endif
    pause 1000
    goto main

I'm also assuming you've set TRISIO and such properly.

Melanie,

Thank you for replying.

Initially, I couldn't get the code to compile without width=mon*1. I've sice removed the *1 and it compiles OK now. No idea why.

Erratic = while it's executing hpwm 1,255,2000 when "width is less than 2" with either version of code, it cycles randomly back and forth to 1,32,2000. While "width is greater than 2" the output is stable.

I'm going to try a while wend in there.

~ Dave

Here's what I'm using since your reply:

INTCON = %10001000 'internal oscillator
OSCCON = %01110000 ' 8mHz
CMCON0 = 7 'Comparators off
GPIO = %00000000 'outputs low
TRISIO = %00010000 'GP4 as input
ANSEL = %00111000 'AN3 analog

'Define ADCIN parameters
Define ADC_BITS 10 ' Set number of bits in result
Define ADC_CLOCK 3 ' Set clock source (3=rc)
Define ADC_SAMPLEUS 50 ' Set sampling time in uS

' Variables
Mon var Word
Width var byte
Pause 100

Main:
    ADCIN 3, mon ' Read channel AN3 to Mon
    width = mon
    if width > 2 then 
	hpwm 1,32,2000
	else
	hpwm 1,255,2000
	endif
    pause 1000
    goto main
 end

[Melanie]

OK, the penny's dropped...

mon = 16 bits, whilst width = 8 bits... you can't put a quart into a pint pot...

try...

width = mon/4

In case you're wondering why /4 instead of /8... that's because your ADC reading is 10 bits. So why not read 8-bit ADC to start with?

[StoneColdFuzzy]

OK, the penny's dropped...

mon = 16 bits, whilst width = 8 bits... you can't put a quart into a pint pot...

try...

width = mon/4

In case you're wondering why /4 instead of /8... that's because your ADC reading is 10 bits. So why not read 8-bit ADC to start with?

Because I'm such a noob that I have no idea how to do that. Now I'm really confused.

So with this change, when the IC reads less than 2 volts on "mon" it should execute hpwm 1,255,2000; more than 2 volts and it should execute 1,32,2000?

~ Dave

[Melanie]

Looks like we have a lot to learn here...

No, it WON'T be two volts....

The ADC returns a number between zero and 1023 (because you are in 10-bit mode), where zero equals 0v on the ADC, and 1023 equals full-scale 5v on the ADC. Each click on the ADC scale represents 1/1023 ie a FRACTIONAL part of 5v.

So if 5v = 1023, then 2v will be two fifths of 1023 (namely 409).

So, if you want the trip point to be 2v and with a 10-bit ADC, your code should be...

Main:
    ADCIN 3, mon ' Read channel AN3 to Mon
    if mon > 409 then 
	hpwm 1,32,2000
	else
	hpwm 1,255,2000
	endif
    pause 1000
    goto main

[StoneColdFuzzy]

Looks like we have a lot to learn here...

No, it WON'T be two volts....

The ADC returns a number between zero and 1023 (because you are in 10-bit mode), where zero equals 0v on the ADC, and 1023 equals full-scale 5v on the ADC. Each click on the ADC scale represents 1/1023 ie a FRACTIONAL part of 5v.

So if 5v = 1023, then 2v will be two fifths of 1023 (namely 409).

So, if you want the trip point to be 2v and with a 10-bit ADC, your code should be...

Main:
    ADCIN 3, mon ' Read channel AN3 to Mon
    if mon > 409 then 
	hpwm 1,32,2000
	else
	hpwm 1,255,2000
	endif
    pause 1000
    goto main

Wow, it's no wonder I was frustrated enough to chew the lips off of a carp!

OK, where is it that I look up the ins and outs of 8 bit, 10 bit and such? I'd love to find a PBP book for Dummies or something like it.

Thanks again Melanie!

~ Dave

[StoneColdFuzzy]

OK, the penny's dropped...

mon = 16 bits, whilst width = 8 bits... you can't put a quart into a pint pot...

try...

width = mon/4

In case you're wondering why /4 instead of /8... that's because your ADC reading is 10 bits. So why not read 8-bit ADC to start with?

So, if I would have used Define ADC_BITS 8, I would have been OK?

~ Dave

[Melanie]

Well, in that case with 8 bit ADC, variable mon should be a BYTE rather than a WORD.

Your ADC range for 0-5v is an ADC reading of 0-255 where 255=5v.

So 2 volts will be 2/5ths of 255 namely 102...

So the IF statement then becomes IF mon > 102 THEN...

The decision to use 8-bit or 10-bit ADC is simply a matter of precision, and you chose whether you need steps of 1/255 or 1/1024 for the ADC span that you are using.

[StoneColdFuzzy]

Melanie,

1/255 is fine.

Where can I go to learn the basics of using AD conversions? It's obvious that I have no clue.

Thanks again for the help.

~ Dave

[Melanie]

Posts #20 and #23 of this thread... and you're almost there... it's real simple... add to that the ADCIN section of your PBP Manual and the ADC Section of your chosen PICs Datasheet.

Lesson 1.

Get a PIC with ADC Input capability and enough pins to drive an LCD Display. Hook it up so you can send messages to your LCD. Put a POT (10K or 5K) across your 5v supply with the wiper to the PIC ADC pin. Write a small program to display what the ADC value is when reading 8-bit. Wind the POT up and down a few times to see digits change...

Lesson 2.

Repeat above with 10-bit ADC input.

You're an expert!

[StoneColdFuzzy]

Melanie,

OK, I contacted my supplier rep and he's sampling me some LCD screens and driver ICs. He gasped and said "Wow, you're finally going digital!"

I also went a step further and ordered the book, Programming PIC Microcontrollers with PICBASIC. Something that I should have done a long time ago.

Thanks again!

~ Dave