Sunday, March 20, 2011

Construct your own DC Power Supply Wall Wart! Variator Reporting.

Alhamdulillah. All Praises to Allah SWT who created and governed everything in this world.

So guys.. we'll be doing something very important for hobbyists here. All electronic circuits require a steady power supply, and you'll get fed up using batteries for testing purposes, which run out of juice for only an hour's worth of running time.. That excludes the electrolytes which leak out after some time.. (NOOOO!!!).....

So.. normally people would opt to: Buy a costly DC wall wart, with fancy controls and an indicator (which is sometimes deceiving) and risk thinning your wallets......

.....or construct their own by buying cheap DC supplies and hacking it to suit their applications. In my experience, after some time the cheap DC supply will be overheated and you'll be left with a fuselage of burnt plastic and a dead transformer.

....or you can opt to take a leaf out of the book of Vortex Electrica and use your own adapters in your house. There are tons of adapters for various applications; Laptop chargers, printer adapters, cellphone chargers (especially old ones), and so on. What's the difference between the ones you buy? Normally adapters for branded stuff have more quality and more protection circuitry. So... This is my collection:

A lot huh? Some of 'em are damaged, and some are okay. Each can be tested easily using an LED and a 100 ohm resistor.

So... the obvious steps for anyone with basics is to cut the wires loose and connect crocodile clippers to them, right?

WRONG! From experience, the weak points are always attributed to the connection between the wire and clip, because the CLIPS SUFFERS THE MOST MECHANICAL STRESS HERE, SO THEY BREAK APART EASILY AFTER SOME TIME. So if you don't want to have to repeatedly re-solder the clips to the wires, the best thing to do is to make separate connections, which can be plugged when in use. In short, see below:

So.. the figure should give an idea. Also, this means that the power from the DC adapter can be plugged into other circuits i.e not only the crocodile clips but also to a breadboard, or any other devices which have the corresponding socket to fit.

Now, another series of ideas comes into play: I want to have.....

a. indicators to know that it is ON, and
b. I want to be able to switch ON/OFF the power at hand, not at the mains where things might get messy, and
c. I want it to be STABLE, not fluctuating power, and
d. I want it to be VARIABLE, not fixed.

So the rest is easy... Add a green LED to indicate ON, a mono-state switch, a filter monolithic capacitor across the terminals, and a variable voltage regulator, like an LM317 or other equivalent components. In short, everything'll look like this:

So as we go along I'll explain the tips and tricks I employed, which may be of use, since we're all about IDEAS at the first place. So here goes:

First Prototype:
Wall Wart (I named it for reference... Heh heh..)

So the figure shows some simple stuff:

1. Solder the male socket wiring to the Adapter wiring. In this picture, notice that the GREY insulation is there, standing by to sheath the exposed soldered part of the wiring. This means BEFORE soldering, fit in the insulation first. You can get that type of insulation from various types of wiring which has thicker wires.

2. The exposed part of the wiring is now covered properly by sliding the grey insulation over it. Take note that you have to make sure the inner part of the wiring is also insulated so that no short-circuit takes place. Note that the adapter has a tuning knob there, with fixed values from 3.0,4.5,6.0,7.5 until 21 Volts.

3. Now, add a plastic cover over all the stress points, and glue it accordingly. This makes a nice, difficult-to-break-apart socket. This means if there are any mechanical stress suffered by the socket, the wiring will out of the way, and the plastic cover will take the load. The figure below explains better:

See that the one on the left is one without the casing, so the break points are easily formed at the soldered points, rather than the one on the left, where the load is shifted to the plastic casing, reinforced with epoxy glue.

Next, a conditioning circuit is shown here:

The conditioning circuit is also a separate entity, as declared in the plan before, which fits in a green indicator LED, an ON/OFF switch, a freewheeling diode (to counter backward EMF spikes), a filter capacitor to stabilize supply, and a female USB port.

Now, why did I use a USB socket? Because I have a lot of 'em, and they don't leave room for reverse connection, which could be disastrous. The male USB connector is wired to the crocodile clips, which we'll explain in the following. USB ports have four terminals, so I combined two terminals together to get two crocodile clip terminals.

So now.... The crocodile clips. The main problem with most clips is also due to the mechanical stress it faces. So here's my design:

So the epoxy glue is very important to secure the connections. Also, the plastic casing protects the wiring and shifts the mechanical load of the wiring to itself. The USB socket is a bonus; it's strong and has only a single orientation when you plug it.

The figure above shows the transition according to the design mentioned above.
First, fitting the wires inside the plastic casing. I must warn you, it is pretty tricky to fit in the wires in such a cramped space.
Second, the clips' wiring and gluing is done.
Third, just to show when everything's in place.

So, the conclusion is that while it takes a bit more time to do this, you'll save more time than attending to the wires again and again when they break off due to the wear and tear effect.

So that's it! You have a sturdy Wall Wart for yourself and you don't need to spend much in constructing one. A variant of this (more hardcore DIY-ing) will be provided in future articles, InsyaAllah. For such a simple project, a lot of drilling down is done to provide IDEAS. So.. hopefully some of them will be of use.

All the best to ones out there struggling with their lives... May we live to please Allah more.

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