• It begins, again.

    08/11/2024 at 03:11 • 0 comments

    Got a temporary pond again from all the recent rain in my area. Pond means the frog chorus comes out, which means tadpoles (or tadpole eggs in the picture above.) Looks like after three years, the third season of raising tadpoles is beginning.

  • Teardown and partial schematics of a battery charger

    03/10/2024 at 04:47 • 0 comments

    I got bored one day, so I cracked open a battery charger I got.  I was curious if it was just a dumb charger when it came to 9v batteries like many chargers out there, or it actually monitored the state of charge.  The model of the charger: EBL-C802. 


    With it opened up:

    It quickly became obvious why this charger requires charging AA/AAA cells in pairs.  It charges two cells in series.  It's likely done this way as a cost reduction measure.  Sadly the main chip that controls the charging is missing a label, almost certainly sanded off.

    Below is a schematic for the AA/AAA charging circuit. There's two circuits for charging two pairs in total.  It's a pretty simple circuit. A mosfet is turned on/off to control charging and voltage of the two cells in series is monitored by the controller chip though a 10K ohm resistor.

    Below is a schematic for the 9V charging circuit. There's two circuits as two 9V batteries can be charged at a time. This circuit is a bit more interesting. It doesn't operate as a dumb charger as the controller chip is apparently monitoring the battery voltage via a resistor divider.  The circuit trickle charges the battery even when the B772 transistor is turned off via a 3K ohm resistor.

    I have some other observations to note about the charger, but it's close to midnight for me. I'll be sure to update the page later.

  • ​Be careful about using ultrasonic cleaners with UV LEDs on PCBs

    02/11/2024 at 15:07 • 0 comments

    A little backstory:  I got invited to a review program a while back and get various products in exchange for leaving reviews.  When I saw I could get an ultrasonic cleaner, I grabbed it.  It's fairly small in size, and the indented usage is for cleaning dental related products and hence why is has UV LEDs for sanitation.  

    I decided to see how well it does at removing flux on a PCB, so I placed a small PCB with some detergent 8 and let it run.  After its 5 minute timer expired I checked it and it was far from done.  After running it again, again, and again (there's no longer runtime timers for it) it got cleaned.  

    Later on I noticed something looked "off." I compared an unused PCB from the same batch with one that I put in the ultrasonic cleaner and saw a stark difference:

    Yup, those UV LEDs apparently faded the soldermask.  Looks like using the little ultrasonic in this manner isn't feasible without either modifying the cleaner by cutting power to those LEDs or by using something to block out the light from them.