Caliper to PC interface, Part II: Data Format ?????? Help ?

Hi people.

I've successfully *connected* my imported caliper directly to a PC. I did not use a microcontroller in between. The interface is NOT RS232. I will detail this whole project in a future posting for those that are interested. Right now I would like to focus on deciphering the data that I get from the caliper.

While I have the *ELECTRICAL* connection and PC software working fine, I cannot decipher the data !!!!

Below are some sample measurements and the corresponding data streams.

a) I took multiple readings for each caliper position because the data seems to change with multiple readings. I've got two opinions on this: 1) the connecting cable is introducing noise into the caliper, which upsets the readings a bit or 2) the internal data in the caliper is changing a bit and my readings are reflecting that. Note: the LCD readout is not changing. I am pretty sure that the bitstream presented is what the caliper is outputting.

b) The data format doesn't appear to be ASCII or Binary Coded Decimal, like some other calipers. It could be Gray Code, but it isn't a standard Gray code.

c) I think I've got the most significant bit in the right direction. ( ! ) If you look at the data going from small (0.002") to large (2"), the data that changes is moving from left to right.

d) The "49d" is the output from my software. 49 = number of bits collected and d = done.

e) The bit count might not be accurate. The data has three long sections of "1s", one at the beginning of the data, one in the middle of the data and one at the end. My software is not breaking those "breaks" out: they are represented as one bit, I think. The actual data in this stream is probably 46 to 49 bits.

f) My best guess is that there are two values in every transmission. The first set seems to the be "LCD Reading" value. The second set I guess to be the absolute position of the head on the scale.

BTW: This caliper outputs these bitstreams about every 300 mSec. The streams themselves are about 0.8 ms in length. I am capturing the streams with the parallel port on a PC.

Thanks in advance for your help.

Someguy

BTW: I have the copy of Circuit Cellar Ink that describes the PC to Caliper interface.

0.0025 to 0.003:

0000000000000000000111001010000000001110111101001 49d

1000000000000000000111000010000000001110111101010 49d

1000000000000000000111010010000000001110111101000 49d

1000000000000000000111010010000000001110111101000 49d

1000000000000000000111000010000000001110111101010 49d

0.002

1000000000000000000101100001111111011101111100000 49d

1000000000000000000101100001111111011101111100000 49d

1000000000000000000101100001111111011101111100000 49d

0000000000000000000101111001111111011101111011101 49d

0000000000000000000101111001111111011101111011101 49d

1000000000000000000101100001111111011101111100000 49d

0.02:

0000000000000000110100111001111111011101001100101 49d

0000000000000000110100111001111111011101001100101 49d

0000000000000000110100111001111111011101001100101 49d

0000000000000000110101001001111111011101001100011 49d

0000000000000000110100111001111111011101001100101 49d

0.02 somewhere else

0000000000000000110100000010000000001110010000001 49d

1000000000000000110100001010000000001110010000000 49d

0000000000000000110100010010000000001110001111111 49d

1000000000000000110100011010000000001110001111110 49d

0.2005:

0000000000001000000001111001111111010101111111101

1000000000001000000001100001111111010110000000000

1000000000001000000001100001111111010110000000000

0000000000001000000001111001111111010101111111101

0000000000001000000001111001111111010101111111101 49d

2.001:

1000000001010000000011000001111110001101111110100 49d

1000000001010000000010110001111110001101111110110 49d

0000000001010000000010111001111110001101111110101 49d

1000000001010000000011000001111110001101111110100 49d

1000000001010000000010110001111110001101111110110 49d



-2.000:

0111111110110000000000001001111111111101000001100 49d

0111111110101111111111101001111111111101000010000 49d

0111111110101111111111101001111111111101000010000 49d

0111111110101111111111101001111111111101000010000 49d

0111111110101111111111101001111111111101000010000 49d

1111111110101111111111100001111111111101000010001 49d




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