Electronics > Repair

HP 34401a DMM with leaking segments

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Zucca:
qu1ck, impressive. Somebody should give you a Keithley 2xxx when you are done with the 34401a.  ::)

Congrats.


--- Quote from: qu1ck on July 08, 2018, 05:40:00 am ---TLDR is I'll have to do a custom board.

--- End quote ---

Probably you will sell a truck of them. Please consider a group order.
Is it possible to squeeze in it a RS232-USB or Serial Bluetooth/WIFI Ethernet (for remote logging) adapter in it? I am thinking how to use the extra space in the front wisely. Also a bigger diplay with the opportunity to placing some fixed label on the side could be neat, with multiple 34401a on the bench knowing what is measuing what with display labels is nice to have. Don't know how to upgrade the labels, probably all my ideas are too complicated to realize.

Maybe creating a dedicated thread in the test&equipment is also a nice call, so other people could tip in.

bitseeker:

--- Quote from: qu1ck on July 08, 2018, 05:40:00 am ---With custom board I will be able to stick the USB out through a small cutout in the front window panel. That will make firmware updates so much easier.

--- End quote ---


--- Quote from: zucca on July 09, 2018, 07:12:00 am ---Is it possible to squeeze in it a RS232-USB or Serial Bluetooth/WIFI Ethernet (for remote logging) adapter in it? I am thinking how to use the extra space in the front wisely.

--- End quote ---

It seems that these two USB ideas go well together conceptually. Having the port in the front only for updating firmware seemed unnecessary (could just have it inside), but if the port is available for logging, too, then that'd be great.



--- Quote from: zucca on July 09, 2018, 07:12:00 am ---Also a bigger diplay with the opportunity to placing some fixed label on the side could be neat, with multiple 34401a on the bench knowing what is measuing what with display labels is nice to have. Don't know how to upgrade the labels, probably all my ideas are too complicated to realize.

--- End quote ---

qu1ck said that he's making this project open, so there may be lots of interesting things to come.

qu1ck:

--- Quote from: zucca on July 09, 2018, 07:12:00 am ---Probably you will sell a truck of them. Please consider a group order.

--- End quote ---
Doing logistics of group order and delivery is not worth it to me. Board designs as well as everything else will be open so anyone can do it.


--- Quote from: zucca on July 09, 2018, 07:12:00 am ---Is it possible to squeeze in it a RS232-USB or Serial Bluetooth/WIFI Ethernet (for remote logging) adapter in it?

--- End quote ---
Yes, stm32f103 usb port works as a serial port. For now it is only used to upload firmware and monitor debug messages but it's entirely possible to send a properly formatted data out of it and/or send commands back. You won't be able to emulate button presses though, my board only listens on the data lines.


--- Quote from: zucca on July 09, 2018, 07:12:00 am ---Also a bigger diplay with the opportunity to placing some fixed label on the side could be neat, with multiple 34401a on the bench knowing what is measuing what with display labels is nice to have. Don't know how to upgrade the labels, probably all my ideas are too complicated to realize.

--- End quote ---
Bigger display will likely not fit, they are a lot more expensive too. Labels are easy to do, I can display them instead of the bar graph below. I think I'll add that feature. You'll be able to set/update/unset label via usb serial command.


--- Quote from: bitseeker on July 09, 2018, 05:42:15 pm ---Having the port in the front only for updating firmware seemed unnecessary (could just have it inside), but if the port is available for logging, too, then that'd be great.

--- End quote ---
Having port easily accessible is super useful for development. I upload firmware 10-20 times during each coding session. Having multimeter taken apart all the time would be PITA.
But yes, the port also streams display data.

floobydust:
I reverse engineered the 34401-66502 front panel PCB mechanical a while ago, it was no fun. Many hours with calipers, lots of slots...

HP's mechanical engineering here has many innovations, actually very good engineering when you dig in.
The PCB sliding in and snapping into place (no fasteners) with a conductive rubber keypad, a complex difficult plastic mold to reduce costs- impressive work.

At the time I thought I had a failed uPD7527 and was designing a replacement front panel PCB that would still use the VFD but with a new MCU and VFD driver. This is for a simple Gen1 34401-66502 replacement. Not to be confused with Gen2 34401-66512 front panel PCB that uses 87C51 and SN75518's and requires different DMM firmware.
I have another 34401a to repair with the polka-dot problem, waiting for parts to arrive. If it is the NEC MCU then I will just finish the replica PCB.

bitseeker:
It'd be nice to combine qu1ck's display with flooby's replica front panel PCB. However, handling of the buttons would still need to be added, right? I assume that's what's meant by "finish the replica PCB."

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