The DataHolster project was completed in 1992. It was awarded 3rd place in Circuit Cellar's Fourth Annual Design Contest. A feature article about the project appeared in Issue #39 (October 1993).
DataHolster Project Abstract
The purpose of this project is to utilize the "ultrasonic output" capabilities of the Fluke 80 series multimeters. These hand held multimeters have the capability to broadcast information about what is on their displays. This little-known feature (I have spoken with some Fluke engineers who are not aware of it) is enabled when the meter's HOLD button is depressed for about two seconds while turning the power on.
It should be noted that Fluke does not support this function as an end-user application. The ultrasonic output feature is used for final testing the unit at the factory. Hence, deciphering the data format was a major portion of this project.
The Fluke 80 series transmits display information via a small speaker (actually a piezo-electric device) to the outside world. This information is modulated using on-off keying (OOK) on about 16KHz. For development purposes, a 3/32" headphone jack was installed in parallel with this speaker to hardwire the signal to the decoding circuit. A microphone type detector was incorporated into the design to satisfy users who do not want to modify their meters.
After figuring-out the Fluke's data format, a small 68HC705K1 microcontroller based circuit was constructed to convert the data from Fluke's format into ASCII and transmit the ASCII values at 9600BPS in RS-232 format. RS-232 was chosen because it is a standard format which most personal computers can read.
The applications for this project are numerous. The Fluke 87 is an extremely versatile handheld multimeter capable of making true RMS measurements. This project can be used as an automated data logger for environmental measurements such as temperature (with a thermal probe), humidity, motor RPM modulation, long-term power line monitoring, etc. Also, this project can be used as an "automated" lab notebook in that the user can instantly record anything measured by the meter.