Adjustable LCD Breadboard Power Supply

I previously used a fixed 3.3v/5v regulated power supply board for my breadboard prototypes.

However, I recently had a situation where the prototype circuit caused a regulator overload causing the supply's internal 5v regulator to short circuit, and supply an over voltage of 12v. This condition was only detected when components started to sizzle, ouch!

The old supply board was based on AMS1117 regulators. These are not ideal for breadboard circuits, as they are NOT short circuit tolerant. If the power lines are accidentally shorted, they can be damaged and go either open circuit or even worse, short circuit.

When experimenting with circuits, it can often be difficult to constantly monitor the supply voltage and current being consumed.

It would be much better if the power supply:

* Displays the Output voltage
* Displays the Current drawn
* Has an adjustable voltage output
* Is short circuit tolerant
* Has an on/offf power switch
* Compact design, not bench top type

Hence this instable...

Step 1: Design

I found a suitable DC-DC adjustable voltage supply with LCD display for volts/amps and case, on eBay for under £4:

Inpur: 5-23v
Output: 0-16.5v at 3A
Voltage drop: 1 volt

It has a large easily readable blue backlit LCD display and comes in a custom fabricated perspex case with up/down adjust buttons and in/out screw terminals. The current displays to 2 decimal places (minimum 10mA). The last set voltage is also retained on power up.

I intended to use it with a 12v input supply and typically regulated down to a 3.3v/5v/9v supply.

However, it didn't have a power switch. So I decided to integrate an internal power switch by inserting it in series with the input voltage supply, and mounting it on the case.

Step 2: Parts & Tools

Parts:
Adjustable power LCD module with case.
Miniature on/off switch (push toggle type).
Connecting Wires.

The switch I used can handle up to 1A at 30 volts DC, which is sufficient for my needs. Bought from banggood.

Optional:
Wire moulded DC socket

Tools:
Drill.
Sharp craft knife
Soldering iron
Hot glue gun
Digital multimeter

Step 3: Assembly

Solder 2 wires to the toggle switch. I
drilled 2 holes for the wires to feed through the to the switch mounted on the top panel. Pass the wires through and hot glue the switch in its position.

Cut the track from the positive input supply to the diode, using a sharp craft knife. This track is visible on the component side of the board. There are two tracks in this vicinity, cut the one nearest the positive terminal, nearest the edge of the board.Check its broken by doing a continuity check between the terminal and the left leg of the above diode (nearest edge of pcb).

Now solder one switch wire to the supply terminal underneath the PCB, and the other to the left leg of the diode above (near pcb edge)

Test the switch works.

I connected a moulded DC socket to the input terminals for easy disconnection from my external 12v supply. For the output voltage, I twist paired a pair of red/black solid core wire for easy breadboard connections.

Assemble the supplied perspex case with the 2 supplied screws.

You can calibrate the LCD module using a digital multimeter and pressing left button on power up. Then simply adjust the up/down buttons until 5v shows on the output meter.

Job done!

Step 4: Results

This power supply module is so cool!

You can easily monitor voltage and current consumption of your circuit.

Its also handy for testing operation with a variable voltage range. For example your final project may operate from a lithium battery with a supply range between 3.3 and 4.2 volts. This scenario can easily be tested.

It can also save you burnng your fingers and components, when things do go wrong! Just keep an eye on the display and toggle the power switch off.

Happy prototyping!