This instructable will detail how to assemble the open source Purple Squirrel Bread Board Power Supply Kit; a small & simple kit for providing 5V and 3.3V power to your projects.
This project is suitable for beginners. Some soldering tools are necessary but even if you've never soldered before this will not be that difficult. You can buy this kit from the Purple Squirrel website or you can gather the parts your self and using the Eagle files from the website get your own PCB(s) made and go that route.
Step 1: Getting Started
Before starting check your kit to make sure you have all the parts.
Your parts list (if you bought this from Purple Squirrel) should include these 16 pieces:
(1) LM317 Voltage Regulator
(2) SPDT Slide Switches
(2) 0.1” Header Pins
(1) 100uF 25V Aluminum Electrolytic Capacitor
(1) 10uF 25V Electrolytic Capacitor
(1) 0.1uF 50V Ceramic Capacitor
(1) PTC resettable fuse
(1) LED, Red
(1) 390 ohm resistor
(2) 330 ohm resistors
(1) 240 ohm resistor
(1) 1N5818 Reverse Protection Diode
Step 2: Assembling the Kit
Once you have all of the parts, assembling the kit only takes a few steps. I've included pictures of each step.
Start with the PCB
Step 3: Installing the Resistors
First we are going to attach the 330 ohm resistors.
You may need to pre bend the leads like the picture to get the parts to fit.
Once the resistor is in the location turn the PCB over and bend the leads a bit as shown…this will hold the part in place while you solder it down.
After soldering the leads down, trim them off so they look something like the picture.
Repeat the above steps for the remaining resistors (390 ohm and the 240 ohm).
Step 4: Installing the SPDT Slide Switches
When installing these remember the leads on these parts do not easily bend. Also orientation is not critical as you can put these in and they will work regardless of which way you install them.
Because the leads don’t bend I put them in to their positions first and then turned the whole assembly over and let the PCB rest on the switches and then soldered the leads down.
Step 5: Installing the LED
The LED, a diode that gives off light, conforms to a polarity scheme. The longest lead is positive (the Anode) and the shorter lead is negative (the Cathode). The PCB shows a flat edge on the silkscreen marking for the LED. This flat side indicates the side that the negative lead or the Cathode should be installed in.
Step 6: Installing the Capacitors
Install the 100uF capacitor first. It’s the largest one of the capacitors and is marked on its side with “25V 100uF” This part is polarized. There is a marking on the side of the capacitor that indicates the negative polarity AND the negative lead is shorter. On the PCB there is a mark on the silkscreen to indicate the negative pin.
Install the 10uF capacitor as you did the 100uF one. The 10uF capacitor has the markings “25V 10uF” on the side. You will also see the same marking indicating the negative side of the capacitor along with the negative lead being shorter.
The 0.1uF capacitor is the smallest capacitor of the three as well as the smallest part in the kit. This type of capacitor is not polarized as it is a ceramic type of device and as such can be installed without any concerns regarding polarity as shown in the pictures.
Step 7: Installing the Diode
Installing the diode is much like installing the resistors. You may find it easier to install if you pre-bend the leads. This part is polarized and includes a line on the body of the part to indicate this as indicated in the pictures. The PCB also shows a polarity marking. The diode acts as a one way gate. If you install it backwards your power supply wont work unless you exceed the diodes reverse voltage rating.
Like the resistors and other parts bend the leads a bit to hold the diode in place for soldering and then trim the excess away.
Step 8: Intalling the PTC Resettable Fuse
There is no orientation requirements for this device. This device is designed to open and cut power should you draw too much current ( in this case more than 500mA) and it will reset after a cool down period and allow you use the circuit once again.
Install the PTC into its position and gently bend the leads to hold in place and solder it in. Once soldered, trim the excess away.
Step 9: The DC Connector Jack
Installing the DC connector jack is rather easy. The leads are such that the connector jack will clip into the PCB and hold itself into place. Once its clipped into the PCB turn the board over and apply solder…NOTE you might need to apply a bit more solder than you think to solder this part down. Don’t worry you can add solder to both sides of the footprint to get a good connection.
Step 10: Installing the 0.1” Spaced Headers
I waited till near the end to put these in because they are installed from under the PCB (see pictures) to allow you to install this power supply into a bread board.
I installed these into the PCB from underneath and let the PCB rest on the headers. This allowed me to solder the pins from the top side of the PCB.
Step 11: Installing the LM317 Voltage Regulator
I waited till last for this part because of its size. The benefit here is that because it size and the length of the leads you can put this part into the PCB and turn the entire PCB over and let it rest on the voltage regulator so you can solder the leads down. Once soldered in trim the excess.
When it is all said and done your power supply kit should look like this when you are finished.
Step 12: Lets Test the Kit :-)
To test the kit we plug a wall wart power supply into the DC connector…you will notice I didn’t plug the unit into bread board because I wanted to have an easy way to measure the output voltage with one hand and take a picture with another.
Once its plugged we switch the ON/OFF switch to ON and you should see the LED light up. I set the voltage selection to 3.3V.
Put the probes on the Vout pins and we see….3.29V.
Now we switch the voltage selection switch to 5V.
Put the probes on the Vout pins and we see…5.02V
There you have it, a fully functional power supply that will give you 3.3V and 5V and up to 500mA of current.
Step 13: Eagle Files
Eagle Files are here