HP3478A considered to be a good multimeter, but lacks some basic functions expected from current models (e.g. relative, auto hold, average).
What I'm thinking to do is to hook up microcontroller to GPIB bus internally so it will provide additional functions.
I already have some idea what the "user interface" would look like. Display and SRQ button are available via GPIB. "Local" button is also available indirectly.
That should be enough to implement basic menu system.
...
Update (January 30, 2018): working prototype is ready
The hardware is very basic. To reproduce it you'll need the following stuff:
github project:
https://github.com/KIrill-ka/hp3478extFunctions already implemented:
- USB interface - allows to execute generic GPIB commands
- relative mode
- xohm mode - measure resistances above 30M
- continuity tester
- min max
- diode tester*
- auto hold
- temperature**
What else can be done:
* Not sure if I want one. It's just a 2w in 3K range. However, beeping may be added.
** Limited to one particular RTD sensor.Update (September 3, 2018):
The thing now leaves inside my HP3478A powered from it's internal supply. The only hardware modification I had to do to the HP3478A was a cut-out for USB TypeB socket.
This process of integration to the HP3478A is not documented yet (TODO), but now there's a guide for basic implementation and a command reference.
The links are on the project homepage:
https://kirill-ka.github.io/hp3478ext/Thanks to
bitseeker for carefully reviewing the documentation.
hp3478ext allows to send generic GPIB commands to a device, so it can be used as a cheap GPIB-USB adapter. For instance, I'm using it with my HP8561E. I wrote a Tcl library implementing some GPIB functions, which I'm going to release very soon.