Radio Shack deals for builders/makers

If you happen to be near your neighbourhood Radio Shack, stop in and you might find some good clearance deals. Look for the items with blue or tan on the price tags.

I stopped in today to look for an audio transformer to build a sound card interface for the radio, and ended up coming out with a couple pieces of 4.5×6″ perfboard, a resistor component pack, and a capacitor component pack that were on clearance. The perfboard was less than $1.50 each, and the resistor and capacitor component packs were $7 and $6 respectively. The component packs are normally in the $25 range I think. Although I’ve already got plenty of resistors and capacitors, it was really the boxes that I wanted. I think of it as a two good component boxes that come with free resistors/capacitors.

My store also had a few Arduino shields that were clearance marked as well.

Might have to pay a visit to some of the other Radio Shacks in the area.

Return loss bridge

The initial version of the Etherkit HF return loss bridge. Pretty simple. Now I need to learn what it does and how to use it.

Etherkit return loss bridge
Etherkit return loss bridge

More workbench gear and parts

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.

Bag o' Parts
Bag o’ Parts

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.

Another battery charger dissection

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.

Cordless drill charger
Cordless drill charger

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.

Battery charger innards

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.

Battery charger guts
Battery charger guts

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.