Products > Test Equipment
Agilent 34401A Front Panel Hacking
mower:
Hello Everyone,
I was trying to fix some stubborn buttons on my 34401A multimeter. In my frustration, I shorted something :-BROKE I shouldn't have and now the front panel is dead. Taking inspiration from user qu1ck, I am considering a project to replace the front panel with my own custom design. https://www.eevblog.com/forum/repair/hp-34401a-dmm-with-leaking-segments/msg3953096
If I'm able to get a prototype working, I was thinking I could add even more features such as sd card data logging and wireless connectivity.
I have another working 34401A at my disposal to sniff out the serial communications to the front panel.
From my current understanding, the logic levels of the serial communications are 0V and 5V, and floating with respect to earth. Is it safe to connect my knockoff Salee logic analyzer to the main board? Since my laptop would be refrenced to earth, the gnd on the meter would become earth refrenced.
Another question I have is, which power rail would provide the most power to my system, and is it acceptable to use a switch mode power supply for increased efficiency? I see that there is +- 18V, as well as the filament AC rail straight from the transformer, originally for the VFD filaments. Do you think this could provide enough current?
I still have a lot to research on my own but I wanted to start a thread to collect criticism and feedback since I know there are many 34401A experts on this forum.
Thank you for your time,
mower
iMo:
There are the two isolated inguard and outguard parts on the mainboard (they communicate via optocouplers). Those are floating, and the front panel is floating too, afaik, and the panel's signal voltage levels are shifted (there are 2 variants of the voltage shift). Therefore you have to be careful with your logic analyzer and notebook (both have to be floating too). I doubt you would find more info on that project than in the above link (and the sources for it on the github).
The filament is powered off a floating AC 6V as you may see in the Service Manual (you have to study too). That could be used for powering your new front panel unit when wired properly (after making a DC voltage out of it you would require for your design).
Kleinstein:
In the 34401 the isolation is between the input section and the GPIB interface part. The dispaly part is connected to the input part.
As long as the DMM is only used with an isolated test voltage it should be OK to connect a logic analyzer, provided the correct local grond is used. Of cause one should not measure mains or other higher voltages while the logic analyzer is connected. A grounded test voltage would also be a problem.
coromonadalix:
hum i think a member issued an pcb substitute on some thread not long ago ...
Do some searches
Miti:
Outguard should not be floating, why would it? It contains the IOs and can be connected to a computer. Inguard should be floating.
Navigation
[0] Message Index
[#] Next page
Go to full version