small breadboard power supply

Having a huge lab bench power supply on your desk can take up a lot of space. Sometimes you just need a stable low current 5-Volt power supply to test a simple breadboard project. This project shows how you can make a power supply that almost takes 0 space.

Step 1 What you need

To make a power supply you will need the following:

Materials:

-Solder
-wood glue or other PVA based glue
-(black) spray paint
-toilet paper
-old newspaper or equivalent
-wire with jst female connector (for power supply)
-wire with jst male connector (for in breadboard or electronics project)
-heat shrink tubing
-a fresh 9-Volt battery
-a not so fresh 9-Volt battery

-low drop voltage regulator, i used LM2931AZ5 (check the datasheet)
-2 ceramic capacitors 100nF (check the datasheet)
-1 electrolytic capactitor at least 100uF, is used an old 470uF (check the datasheet)
-pin layout: since you're checking the datasheet anyway, make notes of the pin layout.
 

note: the datasheet of my regulator said the ESR value of the output capacitor is critical. From my personal experience, you need two 100nF capacitors and one electrolytic  capacitor, or else it will oscillate audible!


Tools:

-multimeter to test the circuit
-pliers to open the battery
-scissors
-soldering iron

optional: a breadboard circuit in need op juice.

Skills:

-handling a soldering iron
-patience


If you already have a 9-Volt battery clip, you can skip step 2.
If you don't want to paint the power supply, you can skip step 11.

Comments

[ratgod]

I love the idea of toilet paper and wood glue, I've never thought of that before.

I have something similar but it's much bigger and it has a socket for the standard 9V wall supply connector. I'm too cheap to buy batteries ;)

I think I will build one of these though, excellent for building a portable lab.

[janw]

Nice instructable. I did build a similar thinga long while ago but mine had a switch added so that it could switch between 5V and 9V. I must admit that I never use it anymore. most of the time I use power from a USB port to power my breadboard for lowcurrent 5V projects

[critiacrof]

Thanks.
My usb port actually doesn't deliver the full 5 volts, plus I don't want to risk blowing my motherboard. So i rather use this one. The switch is a good idea!

[janw]

you could add a small quick fuse to avoid blowing your usbport

[critiacrof]

Sure. But i rather use a bench power supply than a usb port: it can deliver more current and it has a more stable voltage.

b.t.w. this power supply works good on the arduino too: you will be able to drain energy more from your 9-Volt battery.

[aelias36]

Nice instructable! Question though, (i'm probably gonna sound like a complete idiot for asking this, but,) what's the point of all the capacitors? Wouldn't the regulator work just fine by itself?

[critiacrof]

The capacitors have multiple functions. One is to prevent oscillations. Another one is to absorb peak current. Digital circuits can have high peak currents.
And finally stabilisation. The regulator is not capable of instantaniously changing the amount of current it supplies to the output. Without a capacitor it wil respond too late to a dip in the voltage and possibly overshoot. The capacitor gives the regulator more time to respond to a lower voltage.

[aelias36]

Oh, I never knew that. Thanks.