Reading and fixing Chinese scales

[irving2008]

Had a bit of time spare today so knocked up this bread board...



and a few tens of lines of C code later...



Many thanks to 'bogstandard' who rummaged in his box'o bits and found me a couple of cables for the scales which saved me some hassle in connecting.

This is running off a remote 1.5V supply generated using a 555 and a -ve charge pump (nit in pic), generating -6v for the RS232 into the VFD display and -1.45v for the scales and the -ve side of the comparators (uing 311 but will replace with a single quad unit) using two diodes as the reference. The PIC is a 16F877 but again will find something smaller for the final box as really dont need a 40pin device - 14 input pins (6 for the scales and 8 for a keypad), 1 UART so probably a 20pin device will do the job.

Bill/Robin, I know you guys have both done something along these lines already, how did you force the scales into fast read mode (currently I do this by hand) and, more importantly, how did you know when they got there and weren't in some 'hold' mode?