Today I have managed to get the GDE021A1 ePaper display (EPD) working! I used my minimal EPD-Driver board, which implements a flat-flex cable connector and a booster circuit for the display. The booster generates high voltages needed for display operation (around +-25V). The display is driven by STM32F101 Cortex-M3 CPU, mounted on a universal PCB. The picture below depicts my workbench setup (click to see a full-size image):
In my PIP-Watch project I will use a Li-On battery to provide power. Li-On batteries are easy to use in hobby projects: they are light, small, with high capacity, and they come in variety of sizes. Most (not all) Li-On batteries have nominal voltage 3.7V, hence you can directly power your standard 3.3V digital logic directly, using only a simple low-drop linear regulator (e.g. LD59015).
For my first experiments I chose Nokia BL-4C Li-On battery. It’s nominal voltage is 3.7V, charging (maximal) voltage is 4.2V, the capacity is 860mAh.
Software repository location:
The issue this software solves:
Although the Voltcraft multimeter and the UNI-T USB cable are hardware compatible (the USB cable adapter fits into the multimeter connector perfectly), the software requirements are different. Original Voltcraft USB cable, which costs tripple the UNI-T cable by the way, mimics RS232 adapter when plugged in USB host PC. The UNI-T cable uses different chip internally and behaves like a HID device. On the other hand, UNI-T multimeters use different communication protocol over the serial line than the VC870 does.
This software package is composed of two independent parts:
1. USB cable interface in the utd04-cable directory,
2. multimeter protocol decoder in the vc870-decode directory.
The USB cable interface is adapted from other work, see copyrights in the directory. Compile according to instructions in the utd04-cable/readme.2.txt file.
The multimeter protocol decoder is a perl script. Use in a pipe together with the cable interface:
./utd04-cable/utd04-cable -b9600 | ./vc870-decode/vc870-decode.pl
The above commands need to be run under root (su) because of USB access permissions required in the cable interface program.
Note that I have not tested the protocol decoder extensively, there may be bugs (particularly in range decoding).