Electronics > Repair
HP 34401a DMM with leaking segments
qu1ck:
I’m glad you got it working. I will publish the fix on github shortly, including the "no bootloader needed" firmware and better instructions.
To answer some of your questions:
Annunciator line with 4 digits is hexadecimal representation of 2 bytes where each bit corresponds to one of the glyphs on the display. For example 4th bit is for "Man" and 1st bit is for "*". So you see it changing between 0008 and 0009 meaning that "Man" is lit and "*" is flashing.
More is explained here https://github.com/openscopeproject/HP34401a-OLED-FW/blob/master/protocol.md
Continuity/diode mode spitting data out so fast that it crashes the firmware: as wictor guessed it's because of serial printing interfering with spi decoding. When serial buffers fill up because data is coming too fast the main firmware loop is blocked. You see the led on the bluepill flash for the same reason: this means main loop can not catch up to incoming data. This doesn't happen on release firmware so this is not an issue. And you should never use the meter while it's connected to your pc since your frontend will not be floating potential anymore.
coromonadalix:
Yeah i was lucky, nothing bad happened, i made sur not to connect the probes on anything, even my cheap saleae logic analyser clone "cypress fx2" was loading the data lines if the board was not suplied at the same time the 34401a dmm was powered on :phew:
Time to reorder another oled ?? i hope this time i get it loll if you have your old board with the mask pcb problem to scrape, i would take it
You wrote to me your oled display project would be compatible with the old and newests front panels, right ?
thks @Quick1 for your project and help
qu1ck:
New binaries are up on github
https://github.com/openscopeproject/HP34401a-OLED-FW/releases
I will update howto.md soon.
coromonadalix yeah I still have some boards left from first batch, I'll send you one.
New firmware is compatible with both old and new meters, correct.
hakko:
Thanks @qu1ck for the job in protocol decoding... I also was able to do a dirty display for my meter (new panel version) using my implementation. I was tired of stm32 so i used a psoc 4 board that i have around. I used 2 spi ports as slave to get the data from the meter and a 16x2 crap lcd :-DD :-DD
qu1ck:
Yeah, that doesn't look half bad. You will have a hard time with annunciators though :)
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