finding short on motherboards with a shorty (with display)

[CaptainBucko]

After a certain period of operation of the device Shorty Pen (frequent calibrations), malfunctions began.

What FW version? v1.02.03 was released a month ago on the GitLab site.

plus a few photos from the top side load of components from yesterday. Last time I hand soldered 0603 was 15 years ago, and I remember using too much solder. back then. Oh well, bigger the blob, better the job.....

[Pater]

I also assembled short -circuit finder. Thank you for publishing the documentation. I allowed myself to add a current source to the connection.

The code has been redesigned. The measurement is accurate enough. My solution can be found here (only Czech, the translator will do a good job).

[Evi]

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.

[indman]

Evi,thanks! Can I have the Proteus project and the firmware?

[Evi]

Sure!
Anybody can.


Fast and dirty

[mawyatt]

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.

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

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.