Electronics > Repair
HP 34401a DMM with leaking segments
qu1ck:
Did first pass on the board. I would appreciate feedback. I've done much more complex boards before but still, this is not my expertise.
Some notes: height, mounting holes and 16 pin header match the display board so that you solder it directly on top (maybe with a pin header as a strut, which you can cut off later). I noticed now that it should be 33.5mm high, not 35, that's an easy fix.
Data lines are short and nice, 5v data inputs are fed through 10k resistors to protect stm32 just in case. Those pins are supposed to be 5v tolerant.
UART header and boot state solder bridge are only there to make flashing bootloader easier. After that you will always use usb bootloader.
Power is supposed to be fed from unregulated U553 input on the dmm, that's the line that is feeding earth referenced 5v. I don't think that line is sensitive at all, correct me if I'm wrong. That power input will also go to display Vcc.
Voltage reg is placed on a big polygon, but I kinda eyeballed the power dissipation. Need to check the math on that.
Also ignore the pin headers on the render, they won't be there in end product.
HighVoltage:
What PCB software are you using?
qu1ck:
Kicad 5 rc3.
Sent from my moto g(6) using Tapatalk
qu1ck:
Added eeprom, cleaned up and annotated pcb, fixed height.
It's going to the fab! Even if I screwed something up, I'll be only out $10.
floobydust:
I wasn't sure about the physical location, 12V power source etc.
The OLED modules I've looked at have a different pinout. Not sure what OLED part you are using, I'm thinking of the 3.12" offerings. The modules with on-board boost converter are 5V powered with 3.3V I/O to match the SSD1322, using around 150mA at 5V. I think 12V input will heat up the vreg too much.
10k series resistor on MISO is too high, consider R517 215R and R506 5k62 5V pullup on the main ASIC and CPU, I don't think you'll get a logic 0 there.
I use a series resistor between 5V outputs and 3.3V inputs, "5V tolerant" sometimes means the IC has diodes to +3.3V
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