Thanks to Jason/NT7S for enabling my growing homebrew electronics ambitions. I now have a bunch of stuff to add to the workbench.
There’s this big bag-o-parts to augment the parts bin. It’s filled with resistors, capacitors, diodes, transistors, inductors, ICs and crystals.
He also sent along a first version of his HF return-loss bridge kit and an M3 frequency counter/power meter for the workbench. With the return-loss bridge, frequency counter/power meter, a signal generator and oscilloscope, Jason tells me I’ll be able to make all kinds of measurements for testing and characterizing circuits. I guess I’ll need to spend some more time with the Heathkit signal generator to see how operational it is. I’ll also need to pick up some BNC connectors and jumper cables.
Jason also recently acquired a couple of TI Tiva Launchpad boards, so I got his surplus TI Stellaris LM4F120 and MSP430 boards to play with. Not quite sure what I’ll do with them yet, but maybe they’ll push me to brush the cobwebs off the C I’ve learned.
I also received most of the components I’ll need to build some version of a sound card interface that I can use to connect to the radio for using digital radio modes. I think I’m going to have fun working on that project.
The final wall wart dissection (for now) is a dead charger for the battery of a 14V cordless drill. Rated at 18VDC out, this one is just a wall wart that plugs directly into the battery.
Like the previous wall wart, it consists of a large transformer with a simple full wave rectifier circuit. The rectifier circuit on this wall wart is attached right at the secondary of the transformer and adds a capacitor across the rectifier output to smooth out the ripple from the rectifier.
With this one, there appeared to be no continuity on either the primary or secondary side which certainly explains the 0V my DMM was giving me at the plug.
Today’s dissection was a dead battery charger for an 18V Black and Decker FireStorm battery that goes into my sander. The charger died a few years back and I came across it while cleaning out the junk box. The label says it takes 120V AC output and puts out 21.75V DC output. Putting the DMM across the terminals only gave about 3.8VDC.
Inside the part that plugs into the wall is a large transformer (right), like the previous wall wart. At the other end is the part that clips onto the battery. Inside I found a simple circuit with some diodes, resistors and an LED to indicate charging. Any time I see 4 diodes, I think “rectifier”, so I drew out the circuit based on the circuit board traces. Sure enough, I found a full wave bridge rectifier.
Checking the transformer, there was no continuity on the primary side, but the secondary side was fine. Made me wonder how I was getting the 3.8V at the charger terminals.
Based on this, I have a feeling the innards of the next wall wart on the dissection tableworkbench is going to be similar: big transformer with some rectifying circuitry to produce a “DC” output.
Some wall warts, as it turns out, are pretty simple inside. This dead one from an old set of speakers, is just one big transformer inside that case. According to the label, it just takes 120VAC and transforms it down to 15VAC.
The primary side of the transformer measures fine with continuity between the two leads. On the secondary side though, my DMM gives me about 50Ω resistance between the two leads. I’m guessing that’s probably why it was discarded as dead.
It will be interesting to see what an AC->DC wall wart looks like inside.