power supply (now 0.75-30V / 2.7A), part 5.

One last part is needed to put the wires together. Just incase it needed to be taken apart (maybe because things can screw up sometimes? ;-P ) I wanted to be able to de-solder the wires leading to the heat sink from the print board. Therefore I cut out a piece of plexi-glass (I cut a semicircle), drilled some holes in it and mounted solder lugs on them. One for each wire to be connected. After this it was testing time (basically a check to see if nothing explodes ;-).

The piece of plexi-glass is at the front here. Click the picture for a slightly larger, but much clearer version.

The finished back.

The finished front.

Finished from above.

Project completed successfully!

Power supply (now 0.75-30V / 2.7A), part 2.

The past few weeks I have redesigned the circuitry a few times and this is the "latest and greatest". Also I have bought a new transformer with 2x12V coils. Because of this I can use less power when using a lower voltage. This is good because it makes the transistors less hot. The power supply will have two voltage ranges: 0.75 - 7V and 5.5 - 30V. The maximum current will be around 2.7A

The new schematics. Click picture for a larger version.

The board with it's components. A heat sink may be added here and there in a later stage.

This is the power supply close to it's current phase. At the moment the board is connected to all front-side controls. The transformer is wired too. Now the board needs to be hooked up to the transformer and the transistors need to be mounted on the heat sink and wired. That will be done soon.

Test circuit

I have put together a test board of my power supply and it works pretty good. I may do a bit of fine-tuning so I'm not posting the circuit yet but it is something like this with a few modifications. The heat sink this guy uses seems way too small unless he's using a separate circuit to detect overheating but he doesn't speak about that...

Based around the good old 723 voltage regulator.

The multi meter is also finally paying off :-)

Another close up. Breadboard fun...

Power supply (1.5-30V / 2A), part 1.

To be able to do some electronic hobby projects you need a power supply. You also need other things like a multi-meter for example but that's harder to make. Power supplies are much easier to make and often a lot cheaper than one from the shop.

So I'm going to build a 1.5-30V/2A power supply which is sufficient for most little projects.

To start you always need to convert your mains power (110 or 220-240V) to something more suitable like in this case 24V. Because I didn't want to have all those high voltage parts lying around while working and testing the circuit I decided to make the case first and put all the high voltage stuff in there.

Here are some pictures:

That big chunk of metal is the transformer. It turns 220V into 24V. It's screwed on to the bottom of the casing. It's 72VA (which is 72W coz voltage (V) x Current (A) = Power (W)).

The back and the front panels. The back panel holds the socket for the mains cable and the fuse. ALWAYS use a fuse! For this project I use a 500mA fuse. This only protects the house from a power outage. To protect my equipment I should actually use a fuse of (72/220) 0.3A. I have to see if those actually exist...

The front panel holds the switch (which I'm not happy with because I thought it would be pretty blue but it's stupid blue light) and 2 connectors for the output voltage of 24V.

A close-up of the front panel, just because it's a cool photo ;-)

This is the front after putting it together...

... and this is the back.

I forgot to take a photo from the inside with all the wires attached. That might have to come in Part 2.

With this part finished, I now have 24V at my disposal in a safe way!

Mounting a switch on a lamp

Sometimes you need something and you just don't feel like forking out the right amount of money. Or you just like the design. I ended up with this el-cheapo lamp. It was bought at Go-Lo, you can guess about the quality then. Anyway, it has a switch, but it's inside the lampshade. Fair enough, now you know why it was so cheap. We're speaking AU$9 or something. No money left for an easy to reach switch.

So I bought a switch myself. It has to be one that's suitable for mains power, not every switch can do that. Pay attention to that if this inspires you to do the same!

Right, so here's the lamp.

And here's the switch. Good thinking huh?

Top view of the lamp.

Bottom view of the lamp.

Remove the bottom first. This is ugly, sticky stuff that after removig can only be thrown away (in my case).

When it's gone there's a nice hole left and we can admire the complicated inside (not).

In the meantime back at the ranch; The Switch.

The switch requires a hole to put it in. I bought nice special drill bits that are aparently made for glass and tiles. This is the big one...

... and this is the small one. I usually drill holes in 2 stages.

Drilling. The base of the lamp seemed to be made of clay, hardly baked at all, supersoft. Oh well.

I made a nice round hole. Ever noticed that when you drill with a metal drill the holes are actually triangular?

To be able to work properly we have to pull out the wires.

This is tricky. The cord needs to be cut open. Get some wooden stick and put it through the wire effectively creating a cutting surface. Knowing that there are only 2 wires inside, place a knife in the middle and start cutting the wire open for about 5 cm. Make sure you stay in the middle otherwise you may damage one of the inside wires.

The result should be something like this.

Cut one of the wires in half. It doesn't matter which one because we're working with alternating current (meaning the + and - (ground) change usually 50 times a second (50Hz)).

Strip the ends so that about 5 mm of copper is exposed.

Twist the ends together nicely so they seem 1 thick wire.

Put the ends in the switch and fix the wire very tight.

Put the switch inside the lamp and make it stick out through the hole.

Put the switch-cover on and it's done!