DS18B20 thermostat

[Ioannis]

Could you please make a test for me?

Inside the test code part, put a Serout command to monitor the two values MTemp and setpoint

[code]
MTtemp >>4
if MTtemp <= setpoint then
high heater
else
low heater
endif
Serout TX, T9600,[dec MTemp, dec setpoint] 'Please put at the preffered place on your LCD
[code]

Ioannis

[falingtrea]

Are you comparing the temp sensor output data to the value "78" or "780"? If I understand the data format of the temp sensor read code, the data is (temperature * 10) so that you have a resolution of 0.1 deg. Which means 78.0 degrees is 780 decimal returned by the temp sensor read code.

Also in your compare code you are right shifting the temp sensor reading by 4 which is like dividing by 16. This changes the decimal value 780 to 48 which is not what I think you wanted to do. You need to actually divide the temp sensor data by 10 decimal, and then compare. Or multiply the test value by 10 and then compare.

I think what is confusing you is the DEC function. The DEC take a value and returns the specified decimal digit. Kind of like this: [value / (10 ^ n) ] // 10.

[snuff28]

You are absolutely right falingtrea, I just figured that out. Several things I was doing wrong and will explain later, but right now I am taking my wife out to dinner.
Thanks!

[snuff28]

Ok, many many things I did wrong here. First was that I was trying to shift it >>4 to get the number in the lowbyte then trying to compare. Now the code is:

 MTtemp = (MTtemp + 3200)
 IF MTtemp/100 <=  HeaterSetTemp THEN 
HIGH MainHeater
ELSE
LOW MainHeater
ENDIF

I figured since I was trying to compare a word (data from DS18B20) to a byte (HeaterSetTemp) that I should shift the data >>4 and put it in the lowbyte then compare, but since I'm not working with a negative tempature reading I guess it doesn't really matter since all the leading bites are all zeros. The values displayed on the LCD was let’s say: MTtemp=6610 which is 66.10*F. I divided by10 to get rid of the .10 then compaired to 78 (HeaterSetTemp). Works perfect! The other problem was... it seems that I forgot to set the HeaterSetTemp variable to point to anything, so the HeaterSetTemp that was displayed was 146. I don't know where that came from since after looking at the code the HeaterSetTemp var was not pointed to anything, I would think it should have showed "0". For testing I did:

HeaterSetTemp = 78

I thank you to both Ioannis and falingtrea for forcing me to display the data to see what I was dealing with. I should have done that in the first place and I knew that, but I guess I was looking for and easy fix, as a manager for a team of technicians I am huge on proper diagnosing and preach it all the time... but I failed to follow my own words this time.

[Ioannis]

No problem. Glad you did solve it.

Ioannis