• A dumb mistake with KiCad symbols

    7 days ago • 0 comments

    The TL431 programmable shunt regulator is a useful 3 pin chip that I use a lot. In a recent project I used it in the heart of a constant current circuit. I chose the symbol TL431DBZ which uses the SOT-23 package. Most likely I initially designed the board for PCBA and later decided to hand assemble it and use the TO-92 package. I thought it wouldn't matter since I would change the footprint to the TO-92-wide footprint. Of course I was mistaken. Here is the pin table for the TL431DBZ.

    And here is the pin table for the symbol I should have chosen, the TL431LP:

    Notice the pin number assignments differ. The result was that the pads in the TO-92-wide footprint weren't the electrodes I was expecting.

    Fortunately 3-pin TO-92 packages can be rotated to give a different permutation of the pins and this is the hack I will use for the existing boards. The KiCad project has of course been updated.

  • Half a volt matters

    10/23/2025 at 12:16 • 0 comments

    The ANENG A3006 pen type multimeter was advertised for sale at about $10. I have a decent multimeter, but desire got the better for me as this would allow me to measure without taking my eye away from the test point.

    It duly arrived and I eagerly inserted a couple of Eneloop cells into it. Unfortunately the display backlight was dim, barely visible. I cursed: Cheap s***, that must be why it was so cheap.

    Wait, the voltage of a NiMH cell is around 1.2V, so two would provide 2.4V. The multimeter might be able to run with that but I bet the backlight is expecting 3V from a couple of alkaline cells. I bought a six pack and inserted two. Sure enough, the LCD display became readable. It's a pity I can't power this multimeter with rechargeable cells, but hopefully the consumption is low enough for the alkaline cells to have a decent life.

  • Last of the old solder

    09/04/2025 at 09:40 • 0 comments

    So what's interesting about a couple of rolls of solder? The roll on the left was bought some 40-50 years ago, when I was a kid playing around with electronics. The diameter suited valve (tube) circuits assembled underneath an aluminium chassis using axial components, solder tags, and wires, not even PCBs. It went into storage while life happened: getting an education, then a job and a home. A few years back I started owning all my time again so I put it to use. Soon it will be gone. End of an era. No I won't write a song about how good the old solder was. 🤪

    On the right is what I'm using these days. The smaller diameter suits current designs better because it's slimmer and there is a greater proportion of flux to solder. Furthermore it's 63/37 Sn/Pb. (Look up eutectic.)