8000a dou

Data Output Units for Vintage Fluke Meters

This is a collection of firmware and PCBs mean to be used in vintage Fluke meters such as the 8000A, 1900A, etc. They provide the measurements of the meter on a USB serial port and might also provide other features such as the possibility to power the meter via that USB port.

The firmware targets the MSP430G2xx series of microcontrollers despite them being neither vintage nor 5 V devices. They were chosen due to their good availability, ease-of-use, good compiler support, wide range of package options (including DIP), and affordability. (Most modern 5V parts just have internal regulators anyway, due to modern lithography, so we' just be saving us the level shifting, but some devices require more than a level shifter anyway.)

Code is written in C, decode logic and platform-specific stuff is separated as much as possible. So porting this to a different controller should be straight-forward. The build is run by make as a jumbo build.

1900A — Multi-Counter

• PCB is already designed
• C++ code exists, also ported here, but not yet tested

See https://github.com/dariuskl/fluke_1900a_usb_dou

8000A — Digital Multimeter

Firmware — first working version available with tag 8000a-fw-1 Hardware — PCB not yet designed, working on perfboard prototype

The 8000A is a very early multimeter with limited data output capabilities. It offers only signals for the digits, none for the decimal point or range and mode information.

The serial output is default configured to 19200 baud 7N1 and transmits the readings as outlined below.

<overload><polarity><MSD><2SD><3SD><LSD>\r\n

Modifications Required for Battery Pack (Option -01)

The battery pack PCB does not have routing for all signals required by the DOU onto the finger connector. The two-layered board just could not accommodate both the traces required for the batteries and the DOU. This can be fixed with a few jumper wires, though.

TODO: insert a schema showing what points to connect here

Finger Connector Pinout

The finger conector is a card edge connector at the back of the main PCB. It is double-sides, i.e. there might be different signals on the top and bottom side of the board. Most handily, the Fluke engineers put some pracitcal vias with a 2.54 mm pitch through ten of those connections, plus one extra via to the side, but perfectly in grid. This is where a 11-position pin receptable will find its place.

The signal nT is actually not part of the finger connector, but it does have a strategically placed via. As it is next to pin 1 of the finger connector, I assigned it the pin number zero.

Not all signals have suitable logic levels to interface to a 5 V µC (let alone the 3.3 V MSP430), so comparators are used to condition the signals according to the thresholds that I determined for each signal.

(Note that the given high and low voltage levels are ballpark figures.)

Protocol