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To all electronic, robotic or PIC micro controller geeks out there, if you are reading this, I need a favor from you.

I realized that there are many community and forum out there that discuss on D.I.Y. electronic and embedded system projects. Yet, some students and hobbyists still find it quite hard to get what they want to be done, or maybe something that can really satisfy their needs.

If you are one of them, here’s a favor I need from you. If there is such a blog or forum out there doing discussion on such topics, I mean topics on any projects involving PIC micro controller, what would you expect from it? I mean how would you like a blog like that to exist in order to help you in whatever PIC micro controller projects you are working on, be it for competition, for final year project, for fun, or for whatever reason you want it to be.

For those who are interested, kindly let me know how you think bout this idea by posting it in my comment box.

Thank you.

Working with lab power supply is very common for engineering students as we need it to power up whatever project we are working on. However, there are times when we are unable to access the lab, and buying a lab power supply for personal usage might cost a bomb. Hence, I’ve come up with a much cheaper solution, which is to make a power supply unit from discarded computer (desktop) ATX power supply. With less than RM50 and a little modification, I can get a power supply unit with short circuit protection, high output current and highly regulated output voltage.

How can you do it as well? Read on…

Step 1:

Unplug the power cords at the back of your unwanted CPU, open the CPU casing and locate the power supply (normally a gray color metal casing box). Trace and disconnect all the wires connecting from the power supply to the devices and boards. Remove the power supply unit from the CPU casing.

Step 2:

You will need some extra components to convert this power supply into a usable unit.

1. Heat shrinkable tube (to protect unwanted conducting part).
2. A current limiting resistor, typically 330 ohm ¼ Watt (470 ohm may do as well).
3. A power resistor, typically 10 ohm 10 Watt (or greater).
4. An LED.
5. A toggle switch (to turn the power supply ON and OFF).
6. Audio socket/connector (actually any suitable socket/ connector can do).

If you are using audio socket/connectors, you may label each of the sockets with the respective output voltages using liquid marker.

Step 3:

If you are using a power supply from discarded computer, it is advisable to discharge it by letting it sit unconnected for a few days. However if you are using a new unused ATX power supply, you may straightaway proceed to the following.

Remove the screws locking the power supply with its cover. You’ll probably have a power supply similar to below:

Notice there is a bundle of long wires with different colors soldered to the board of the power supply. Each color represents different voltage level:

- Black = 0V (Ground)

- Red = +5V

- White = -5V (some power supply do not have this voltage)

- Yellow = +12V

- Blue = -12V

- Orange = +3.3V

- Purple = +5V for standby (normally not used)

- Gray = Power ON (output)

- Green = Turn DC ON (input)

Cut off these wires, but make sure you LEAVE A FEW INCHES for future use. Bundle the wire of same color together.

Step 4:

Here comes the hard part. You’ll need to drill holes on the casing of the power supply to mount the audio socket/connectors, LED and toggle switch.

1. Measure and mark the area to be drilled with a tap and hammer.

2. Use drill bit of appropriate size for component mounting.

3. Remember to drill holes for mounting LED and toggle switch as well.

There is no standard way to go around, just make sure you do this carefully and do not break the casing.

Step 5:

Mount and screw the audio socket/connectors to their respective holes on the casing. Next, connect all parts together as follow:

1. Connect one of the red wires to one of the power resistor’s lead, and the remaining to the socket labeled +5V.
2. Connect one of the black wires to the other lead of the power resistor, one black wire to a 330 ohm (or 470 ohm) resistor attached to the cathode of the LED, one black wire to the common terminal of the toggle switch, and all the remaining black wires to the socket labeled 0V.
3. Connect the yellow wires to the +12V socket, the blue to -12V socket, the grey to the anode of the LED, and the white (if your power supply have any) to the -5V socket.
4. Connect the green wire to the normally opened (NO) terminal of the Toggle Switch.
5. Some power supplies may have either a gray or brown wire representing power good. Connect this wire with one of the orange (+3.3V) wires; if not your power supply will not work.
6. Finally, make sure all soldered connections are insulated with the heat shrinkable tube and organize the wires accordingly. Mount the LED and toggle switch to their respective holes. If possible, fix the power resistor to the heat sink of the power supply.
7. Make sure there is no short circuit connection (beware that the casing of the power supply can conduct electricity). Cover and screw the casing back to the power supply unit.

There you go, a self-modified power supply unit for your project.

Works pretty well with my project

Please bear in mind that there are a few precautions you need to know:

1. This modified computer power supply is suitable for testing purposes and powering simple circuit, but its performance can never match a good lab power supply. Hence, if you intend to do more than just testing, it is more advisable to get yourself a lab power supply.
2. Line voltage can kill, so be extra careful when dealing with the supply power unit.
3. Make sure no metal dust fall into the circuit board of the power supply when drilling.
4. The power resistor is used to dissipate power when the power supply unit is not connected to any load. Hence it will get hot if the unit is turn ON. A good suggestion is to mount it onto the heat sink of the power supply.

Mounting power resistor onto heat sink

Hope this DIY information is useful to you. Have fun…