Category: Electronics

Found one of these rummaging around in the car the other day.

If you have no idea what this is or don’t get what it’s for, ask your parents.

The cassette player in the car kept spitting it out, so I figured I’d open it up to see what was inside.

Surprisingly simple inside and much less than I expected. Just the magnetic read/write head and a single circuit board.

There are just a couple of capacitors and a couple of resistors (on the other side of the board), so it’s a very simple circuit.

The resistors are pretty big, 820 MΩ, presumably to knock down the input down to something the cassette player can deal with.

My first attempt at building a circuit using the ugly construction technique. It’s supposed to be a simple oscillator circuit using a J310 transistor.

One of the advantages of ugly construction is that if you’re working from a schematic or circuit drawing, building is pretty easy. I found that soldering components to the copper clad required a bit of patience, because it’s essentially a very large heat sink. Put the soldering iron on the copper clad, add solder until you get a good sized pool, leave the soldering iron in place and place the component.

For this particular circuit, V_cc is applied to the big resistor with the free lead and output is off the capacitor with the free lead. I soldered on a piece of wire to make the ground connection easier. Haven’t applied power to test it out yet. Will see if it works later on.

Found a DSL phone line filter from the Earthlink DSL days in one of my junk boxes. This particular one is an Excelsus Z-BLocker DSL filter Model Z-230PJ. The www.excelsus-tech.com website printed on the back is dead, but a bit of Googling brought me to Pulse Electronics, so maybe there was a name change or some merger-ing happening.

Since I’m not likely to be going back to DSL service any time soon, I figured I’d have a look to see what’s inside. DissectionDisassembly was pretty easy. The top is just held in by clips and not glued, so a little bit of prying with a thin bladed screwdriver and it pops right off. There’s not a whole lot to see inside: a couple of inductors and a capacitor soldered onto a circuit board.

It’s a pretty simple device, just an inductor on each line with a capacitor in parallel (I think that makes it a low pass filter on each line).

The inductors aren’t labeled on top, so I don’t know what value they are. If I’m reading the code correctly, the capacitor is 22 μF.

I wonder what kind of project I can come up with to make use of this…