Introduction: Cheap Variable Power Supply LM317 Under 10$
I did not have an atx power supply or a professional lab power supply, but as any electronic enthusiast would know, electronics all operate at different voltages. This makes rapid prototyping very difficult if you don't have a variable power supply to provide these exact voltages.
My build is very versatile, and the simple schematic allows for the build to be as small as 2x2 cm. This allows for integration into any project with a higher power source. I used the schematic to make an external power supply for proto typing
My build was heavily inspired by THIS build, but I upgraded his idea by having a lcd screen with voltage read outs, precisely tuned voltage selection for common voltages with a multipoint switch, and also a potentiometer for a wider control.
The heart of this setup is a LM 317 IC. The best part about it is that it offers short protection, and switches itself off at extremely high amp draws.
Potentiometer, or a set of resistors for prefixed values(see ahead)
Heat sink (Optional, I did NOT use one, and it is working perfectly.)
A proto board to solder your circuit
12 volt power supply (lower is possible but is not preferred.)
Mini millimeter with led/lcd like THIS ONE (under 2 dollars)
Step 1: Build It
I strongly suggest you follow the steps for assembling the electronics from the schematic above
I will thoroughly explain the modifications that I have done to improve his design
My Hacks- LCD
From the parts list, you can see the exact led/lcd that I used. The great thing about my inexpensive lcd/multimeter module is that it is very small, and has an actively updating voltage readout. This means you can actively see the voltages that you are cycling through, and makes for a less accident prone environment. I cut a small area in the project enclosure for the led/lcd to pop out of, and simply hot glue it in place like the picture above. This is wired in parallel to the output of the chip.
My Hacks - Preset Voltage Values
What this is, is that it is a 4 pole 4 throw sider switch. This means that it has 4 positions unlike the regular 2 position switch. Using the rotary potentiometer, and the an EXTERNAL multimeter, I measured the exact resistance required to get the popular voltages I wanted, namely 3.3 v, 5 volt, 12 volts.
My way for getting these pre-set values were via getting a rough idea of the voltages by dialling in the variable potentiometer, and then measuring its resistance. Then I took that and added or removed resistors tiring to get closer to the exact value with the multimeter hooked up to the outputs. It is basically like a game or hot and cold, You are trying to get closer to the value with the given information of hot and cold.
If this part did not make sense then think of it as many 'potentiometers' with already dialled in voltages. We use a simple switch to cycle between these 'potentiometers'. Instead of potentiometers, I find and use fixed value resistors. This allows me to have exact voltages in addition to a potentiometer for those variable voltages.
If this part still confuses you then drop a comment below, and I shall answer it.
My Hacks - Case
Ok, this one is quite simple to reproduce, and very easy to make. Just take any compact project enclosure, and make a few holes for your parts to stick out of. You can do this with a dremel, or even a pen-knife if you are feeling ambitious
My Hacks - Alligator clips
This makes connecting anything ridiculously easier. steps are quite self explanatory. If confused look at the pictures.
Step 2: Final Thoughts
The lm317 chip is a very versatile and easy to use chip with short and over amp protection.
The only downside is that the chip cannot handle high amounts of current draw, but that could be a good thing to keeping the project safer, and the power supply cooler. It also makes room for a future project with a beefier power supply perhaps one based of an atx power supply.