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Ok cool! Thank you both of you for the info. That's basically what I needed and I don't know how I overlooked the necessity of the LEDS for the using clock and data to set the mode and zero.
I do have another question though... Where did you source the -1.5v for ground? The scale's ground?
Sorry if this is obvious, I'm still learning and I gotta start somewhere
If you squint at my picture long enoughyou should be able to make out a 5v regulator with a resistor + Red LED giving about 1v5 above the regulator's 0v, this is taken to the common ground so giving -1v5 (regulator 0v and PIC Vss) & +3v5 (reg +5v and PIC Vdd) from a floating PSU input.
No, the scales ground (battery +ve) is the same as the PC's ground i.e. Earth potential, the -1v5 is the scale's power supply input (battery -ve).Where did you source the -1.5v for ground? The scale's ground?
Oh my... I appologize. I was too busy looking at the code and I didn't scroll down far enough to see the picture you attached.Originally Posted by BillTodd
If you squint at my picture long enough
No, the scales ground (battery +ve) is the same as the PC's ground i.e. Earth potential, the -1v5 is the scale's power supply input (battery -ve).I was referencing the diagram on your site.
Almost time to go home so I can work on something fun.
Well after some extensive messing around it seems that I need to learn assembly... I've been programming these little chips for awhile now using MikroC and it's worked quite well until now. Unfortunately, it looks as though the code just doesn't run fast enough to pick up those 90khz signals unless it's done in assembly. Simply reading the value of COUT is taking serval intructions (when you look at the assembly version), which just isn't necessary.
No biggy
Be back soon!
PIC assembler is easy only 35(?) instructions (it's the carry that always throws me - is it set or reset after subtraction???? - catches me out every time!)Well after some extensive messing around it seems that I need to learn assembly
I don't think HLLs like 'C' are ideal for programming these little controller chips. PICs in particular benefit greatly from careful optimisation even in when writing in assembler.
Is it possible to embed and call assembler routines in your version of C?
I can place assembly directly into the C code and have done that with some minor things... However, I'm not certain how to use them together in a looping or conditional situation.
If you want to just concentrate on the convert and display device, and are happy using async serial instead of I2C, I could let you have a copy of my obect code and a run down of the interface protocol? (may even have the board design somewhere)
Actually that would be really nice... I've been spending some time the last few days getting a grasp on programming the PIC's in assembly. It's really quite interesting. I probably won't use your code directly and as more of a guideline. Not because I think I could do it better, but because I still want to learn assembly for these chips.
If you have a larger picture of the scale schematic you posted that would help quite a bit.
Thanks again for all of your help.
Like most things, you have to get your knowledge up to a 'critical mass' Once you can get the thing to compile you're pretty much thereI've been spending some time the last few days getting a grasp on programming the PIC's in assembly.
It might just confuse youwon't use your code directly and as more of a guideline.
The source should open with MPLab 8 or later.
Keep us informed of your progress
Alright so I've made some pretty decent progress!
After going through the typical blinking LED, input, etc. stuff I finally decided to take a crack at reading this signal. To my surprise, my first try worked!
I decided my first step should be simply determining if the PIC was reading the signal correctly. This was done by turning a pin on when it sensed the clock was high and turning it off once the clock went back low. This turned out to be surprisingly simple and FAST... Here is the little bit that does that portion:
I then connected one channel of my oscilloscope to GP5 on the PIC and one channel to the scales output (which was also going into the pic).Code:RL1 btfss CMCON,COUT ;wait for clock high GOTO RL1 XORWF GPIO,5 ;toggle GP5 RL2 btfsc CMCON,COUT ;wait for clock low GOTO RL2 XORWF GPIO,5 ;toggle GP5 GOTO RL1
Check out the result in the attached image.
I would like to add that I could NOT get this to work correctly using MikroC... Nothing against it, but the speed difference is quite obvious.
One little change to that code... GPIO,5 should actually be GPIO,1
Code:RL1 btfss CMCON,COUT ;wait for clock high GOTO RL1 XORWF GPIO,1 ;toggle GP5 RL2 btfsc CMCON,COUT ;wait for clock low GOTO RL2 XORWF GPIO,1 ;toggle GP5 GOTO RL1
You're a fast learner
Be aware there pitfalls if you talk to the GPIO using those infamous read-modify-write instructions sometimes you get away with it sometimes you don't (there's full explanation on the microchip site).
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