Data Logging Weigh Scale
Implemented here is a data logging digital weigh scale. The original scale was gutted, leaving the four strain gauges, one per leg. The main controller is an AtMega32. An AD623 is used for differential amplification of the strain gauge signal. The LCD is a graphic 128 x 64 module. There is a DS1307 RTC for time keeping, an FTDI232 for USB to serial bridge and via the 74hc244 for level shifting, an SD card slot for data storage. The off board power supply used a MAX710ESE for switch mode boost/linear buck.
The code, upon boot, calibrates the scale and then indicates ready. The user is weighed and then identified by passing the previous weight thru a window function. Finally the current weight is stored and the previous two weeks are displayed in graphical format. After a short delay the scale turns itself off by toggling a flip flop tied to the enable line of the MAX710. Of the available 32k flash, 28k was used mostly due to the large LCD fonts.