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finding short on motherboards with a shorty (with display)

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mawyatt:

--- Quote from: Evi on June 02, 2024, 12:45:53 pm ---My variant.
1. No current when no measurement - battery longer life. Lower measurement current due to absence of 2 Ohm resistor.
2. Simplyfied calculation: Rx = (volts / 27) / (current); More accuracy.
3. My SW stored and displays last measured Rx minimal value between measurements instead of -----. It is more convenuent.
4. Current measured on 1 Ohm resistor during calibration and stored in EEPROM.

--- End quote ---

Nice work!! Not a criticism just a comment, might consider added another protection diode in reverse on the op-amp input to protect for negative input voltages. The circuit shouldn't generate negative voltages wrt ground, however a circuit under test could have a residual negative voltage wrt to ground. Also might consider moving the protection diodes on the other side of the 1K resistors, or even better add an additional pair of back to back diodes across the force terminals, which should provide a high degree of instrument protection against rogue DUT voltages. Some folks have reported damaging LCR meters with large capacitors that have a residual charge, so these kinds of things do happen :o

Anyway, all these are clever circuit implementations :-+

Best,

Evi:
Of course.

CaptainBucko:
My Shorty is up and running (mostly) - I made a mistake during component substitution for U1, selecting a 1.2v instead of 1.85v. That's on order, but has delayed the final fitting and calibration. Corrected BOMS are attached.

I also blew up the first STM32 Micro as a result of a dumb ground loop issue that caused 15vAC on the tip of my soldering iron. The STM32 drew 60mA instead of 3mA on power up! That took a while to track down the fault and root cause.

Also, my cheap Chinese ST-Link v2 clone had the plastic embossed triangle (indicating Pin 1) on the 2x5 PIN header in the wrong location with respect to the actual pin wiring. That also cost me a bit of time.

Once these issues were straitened out, programming was strait forward using STM32-Cube-Programmer. While putting in an order the 1.85v LDO above from Mouser, I decided to add some STM32 Dev Boards to get to free shipping. Reading more on this device, I think it will replace my aging ATMEGA platforms.


Evi:
I found it usefull to make it as plug-in module for M5STICKC.

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