Matrix user forums

Ben,

I've been working from Eric's DS1820 program as the basis for understanding why I have been unable to get my replication of his experience to work properly.

I created a stripped down version of Eric's program that reads one DS1820. In the program I included LCD diagnostic statements to report return values from the DS functions available in V4.2 of Flowcode

One of the problems encountered is that the V4.2 Flowcode specifys that the variable return values from some of the functions are BYTE's. This looks incorrect as the LCD call diagnostic reports a character of 3 horizontal hashes ( one on top of another) - changing this return variable to an integer reports a 0. This is further supported by Eric's program specifying them as integers instead of bytes as V4.2 of Flowcode indicates they should be.

I would greatly appreciate your help in looking at my simple program that still wont function.

Im very focused on getting this to work and any help would be grealy appreciated.

I have attached the file

Thanks !!

Hello George,

I tried your program and it actualy works. It needs of course to be refined but the basic principles are correct.
Now I am even more convinced that you have a hardware problem somewhere.
Look at the attached diagram with simulation. I had to make some changes to make it run on my hardware ( lcd to portD, sensors to portA0, pic18F452 )
I also tested it on my hardware and there it gave the same results.
2 of the 5 DS18 sensors are connected to PORTA0. Your program reads out device 1, which is the boiler sensor ( devicecount starts at 0 )
The temperature of that sensor is set at 47.0 Β°C.
Here I made some correction to your program. If you multiply the value by 10 and devide it afterwards by 16, then you get the temp value directly in Β°C with a resolution of 0.1 Β°C. You just need to convert this value to string and add a decimal comma.
I also removed the getpadbyte instruction. It is not necessary if you only want to read the temperature on a DS18B20.
In my original program this was needed to allow mixed sensors DS18S20 and DS18B20.

So, I think you are on the right track.
Just figure out what is wrong with your hardware.

Best regards,

Eric

Eric,

Thanks for taking the time to put your reply together !!!

I wired up exacty as in your schematic - checked and double checked

I get all 0's when I run it - including a 0 for get temperature - i added a loop around the code to see if I could get any number other than 0 to show up for temperature - no success

I tried both a 0 and a 1 for device number with same result

Interesting that with no DS18B20 connected the results are the same - it's as if port A0 doesnt see the DS

I tried 5 separate DS18B20's to rule out a defective component and also 2 PIC18F452's - same result

Occasionally I would get random numbers on the LCD to the right of the print string diagnostic calls ?? - thought I may have an intermittent connection - checked all and all ok -

Interesting that some of the functions ( like get count) would occasionally hang up and stop program execution and I needed to hard reset to get the code to run to completion -

Other than adding a loop I made no changes to the code we are looking at.

I tried a 4.7K pullup and a 5.6K pullup on the DQ line of the DS and no impact

All supply voltages to PIC and DS are ok at 5.06V - all hardware checks out

Could it be a flowcode setting for the 18F452? Im using a PICKit2 from MicroChip.

This one is a tough one - LM34's with LInear outputs to A/D sure are easier to implement

I would really like to get the DS going -

Please dont feel obligated to spend any more time on this but would certainly appreciate any other thoughts you may have

Best Regards,
George

George,

What crystal frequency do you use?
It can be a timing problem.
I use 8 Mhz.
Also: try adding delays of 100 ms after each command


Eric