Build Instructions for Voltage Shifter Circuit

Sunday, October 13, 2013

Last post covered the design considerations for the Voltage Shifter required for the Mixed Scale DRO Controller. As promised, in this post I will provide detailed build instructions for this circuit. The board is designed to work with up to four scales and has three power rails. One provide 3.3V power supply to the comparators and [potentially] iGaging scales; the other two can be set to any voltage between 1V and about 18V. Although the firmware doesn’t [yet] support glass scales or tachometer input, this board is ready for them.

3"x4" 1200 hole stripboard
with a track cutting tool

Voltage Shifter Circuit for Mixed Scale DRO Controller

Saturday, October 12, 2013
In the last post I introduced the new version of DRO controller that is able to read a mix of common digital scales. You might recall that “Mixed Scale” controller uses the same MSP430 Launchpad development kit as the “Basic” version, but requires a bit of extra hardware. Unlike the the iGaging scales, which work quite comfortably with the 3.3 Volt power supply, most other inexpensive capacitive scales use 1.5V (nominal) power supply. This means that their outputs can’t be reliably read by the MSP430 microcontroller. Similarly, glass scales and quadrature encoders use 5V power supply. MSP430’s inputs can tolerate up to 3.6V, so connecting the glass scales directly to the Launchpad will permanently damage the inputs.

Mixed Scale DRO Controller Project Update

MSP430 Value Line Launchpad DRO controller connected to a level shifter board
Mixed Scale DRO Controller with MSP430 Launchap

So far the DRO controllers I’ve designed have been able to read only the IGaging (Shahe) Remote DRO scales. Lately I’ve been getting an increasing number of requests for a firmware that could read the standard “chinese” linear scales.A few months ago I started working on a new version that would do just that. Although the project is still a bit rough around the edges, I’m pretty sure that the hardware will stay unchanged and any future updates will be done via firmware. Rather than holding off until the whole shebang is done, I decided to post the stable version of the firmware. In the next few posts I will provide details for the project, design considerations, build instructions and firmware implementation.