MEASURING FORCE ON BALANCE USING AN ELECTRONIC BALANCE FROM THE SERIAL PORT

Question

Hi,
I am trying to measure FORCE using an electronic BALANCE from the serial port. My measurements are strange! The BALANCE sometimes give ZERO reading! Is it because of the sample rate, baud rate etc? I have attached the readings concerned.
Attachments:
databalance.doc ‏144 KB

Answer 1

I think your problem is due to the way you read the weight :
1/ask the balance to send the data
2/oversee the byte number on the serial port until it is constant
3/read the bytes received
4/convert to number
During step 2, you compare the bytes at serial port with the previous value. So far, you have been very lucky to be able to read something : the answer here is always ZERO since the readings occur BEFORE the balance has been able to send anything! means that your loop stops immediately (if you are not convinced, jujst add an indicator to display the loop index. However, since you added a wait (0.8 s), when going to step 3, the balance has had some time to send something. Here, you should not have read again the number of bytes at serial port, but that unwillingly corrects the previous error and you can read most of the received data...
You should modify completely your algorithm. Usually, a balance send the weight as a string with some terminator (RC or LF). Accordingly, the algorithm should be :
1/ask the balance to send the data
2/read the serial port, concatenating the received chars until a terminator char is received or a timeout has occured
3/convert to number
CC
Chilly Charly    (aka CC)
         E-List Master - Kudos glutton - Press the yellow button on the left...