General Overview

As the world around us becomes more and more environmentally conscious, “alternative energies,” such as wind, hydroelectric, and solar power, are becoming more prevalent in our day-to-day lives. DigiKey, in keeping with our pursuit of leading-edge technology, has developed a simple process to create your own solar charger, allowing you to become more “green” and take that first small step in preserving the environment.

Tools needed: Soldering iron, utility knife, wire cutter/stripper, drill, needle-nose pliers, small slotted screwdriver, Phillips screwdriver.
Miscellaneous: Hook-up wire, double-sided tape, marker.
Time required: 1-3 Hours

Download Step-by-Step PDF

Order complete parts list for the solar charger

Prep the prototype circuit board: Trim it down, file the rough edges, and drill the mounting holes.

Assemble the circuit and solder components into place.

Modify the enclosure and mount the board.

Do the final wiring and test. Make sure the positive and negative side of the solar panel are connected correctly.

Tools & Schematic

Parts List

Step 1: Prepping the Prototype Board

First, two of the corners on one of the narrow ends of the board need to be notched out to clear the cover posts. Using the holes that are 3 positions in from each adjacent side, gradually drill these out to a 3/8” diameter. Once the holes have been drilled, the excess board material can be removed using a side cutter, and the rough edges can be filed smooth.

At this point, the board is still too long to drop into the enclosure. The extending tab created by the notches needs to be shortened. This is achieved by scoring across the first set of holes with a utility knife on both sides, and removing the board section by flexing it up and down. Again, the rough edges should be filed down.

Mark and drill 1/8” holes in the board to match up with the two PCB standoffs closest to the notched end of the board. The holes should be drilled eight hole positions down along the side, and centered between the 2nd and 3rd hole positions in towards the center of the board.

Align the front edge of the USB connector on the notched end of the board so that the connector opening extends approximately 0.1” beyond the edge, and the terminals match up with the holes in the board (it will be 0.1” off center). Mark and drill out 1/16” holes in the prototype board for the mounting terminals. Elongate these holes to accommodate the rectangular shape of the mounting terminals.

Step 2: Circuit Assembly - Component Placement

Press the USB connector (X2) down flush with the PCB and bend the mounting terminals at a right angle towards the outer edge of the board. Note that the terminal spacing on the USB connector is not on a 0.1” grid, so care must be taken while placing it onto the board. Solder the mounting terminals to the PCB hole just beneath the bent portion of the terminals. Solder the 4 USB connector pins to their respective holes in the circuit board.

Bend the MBR150 diode (D1) to a 0.4” lead spacing. Place the banded cathode end of the diode in the PCB hole just behind pin #1 on the USB connector (X2), with the anode end parallel to the length of the PCB. Pin #1 on the USB connector is the leftmost pin with the open end of the connector facing toward you. Solder the diode into place, and cut off and save the excess lead lengths.

Bend the leads of the 100uF (C2) capacitor to 90 degrees in the opposite directions from each other, staying as close to the bottom of the capacitor as possible. Bend these horizontal leads in a downward direction to a 0.3” spacing. Place the capacitor on the board with the positive terminal going into the hole inline and adjacent to the anode of diode (D1), and make sure the negative terminal is in line with pin #4 of the USB connector (X2). Solder the capacitor into place, and cut off and save the excess lead lengths.

Place the voltage regulator (IC1) such that pin #1 is in line with the negative terminal of the 100uF capacitor (C2) and 4 holes away from it. Pin #1 of the regulator is the leftmost pin when viewing it from the front, which contains the part number and logo. Solder the regulator into place.

Place the 10uF capacitor (C1) diagonally as close as possible to the regulator (IC1) with one terminal in line with pin #1 of the regulator, and the other terminal in line with pin #2 of the regulator. Note that there is no polarity on this capacitor. Solder the capacitor into place, and cut off and save the excess lead lengths.

Remove the plastic alignment pins from the 2 position terminal block (X1) with a knife. Place the terminal block as close to the 10uF capacitor (C1) as possible. Its terminals should be in line with the capacitor terminals, with the terminal openings facing away from the capacitor. Solder the terminal block into place.

This completes the component placement on the circuit board.

Step 3: Circuit Assembly - Component Connections

Input Voltage: Using one of the saved excess lead lengths which were cut off, connect terminal #1 of the terminal block (X1), the leg of the 10uF capacitor (C1) that is in line, and terminal #1 of the voltage regulator (IC1).

Ground: Using another excess lead length, connect terminal #4 of the USB connector (X2) to the negative terminal of the 100uF capacitor (C2). Using a third excess lead length, connect terminal #2 of the terminal block (X1), the unconnected leg of the 10uF capacitor (C1) which is in line, and terminal #2 of the voltage regulator (IC1). Using a fourth excess lead length, connect terminal #2 of the voltage regulator (IC1) to the negative terminal of the 100uF capacitor (C2).

Output Voltage: Solder bridge terminal #1 of the USB connector (X2) to the cathode end of diode (D1). Solder bridge the anode end of the diode to the positive terminal of the 100uF capacitor (C2). Using another excess lead length, connect the bridged junction of the diode anode (D1) and the negative terminal of the 100uF capacitor (C2) to terminal #3 of the voltage regulator (IC1).

This completes the component connections.

Step 4: Enclosure Preparation

In order to make connections to the solar panel and an external USB cable, it is necessary to provide openings in the enclosure. As far as connecting to the solar panel is concerned, a hole drilled in one end to a diameter sufficient for the connecting wires to pass through is required.

For the USB connector, a rectangular notch needs to be cut into the bottom half of the other end of the enclosure that is deep enough to allow the board to drop down onto the PCB mounting bosses.

Place the circuit board into the enclosure with the USB connector angled down and against the inside wall of the enclosure. The back half of the board should rest on the cover posts at the opposite end. Mark the width of the USB connector with a utility knife on the inside wall of the enclosure all the way up to the top of the side. Remove the board and make a line 7/16” up from the bottom of the inside of the enclosure that intersects the two lines indicating the connector width. Remove this rectangular section from the enclosure by drilling numerous holes and cutting away the excess with a utility knife so that the board lays flat on the mounting bosses and there is sufficient clearance for the bottom edge of the USB connector.

Step 5: Final Wiring and Testing

Place the PCB into the enclosure and secure it in place with self-tapping screws. Cut, strip, and tin the ends of two pieces of wire approximately 12” long. Pass the wires through the hole on the end of the enclosure and fasten them to the terminal block using a small slotted screwdriver. Remove the cover from the solar panel, and pass the wire through the entry hole, beneath the cable clamp, and fasten the wires to the appropriate terminals with a Philips screwdriver.

NOTE THAT THE POSITIVE SOLAR PANEL TERMINAL IS CONNECTED TO THE FIRST POSITION ON THE TERMINAL BLOCK, AND THAT THE NEGATIVE SOLAR PANEL TERMINAL IS CONNECTED TO THE SECOND POSITION ON THE TERMINAL BLOCK!

Once the connections have been made, place the solar panel in direct sunlight and verify that the panel is putting out voltage. Next, verify that the regulator circuit is functioning by checking to see whether or not 5 volts DC is present at the USB connector. The leftmost pin, pin #1, is positive, and the rightmost pin, pin #4 is negative.

If everything is functioning properly, replace the cover on the solar panel, and fasten the top of the enclosure to the bottom half with the four screws. If desired, the enclosure can be affixed to the back of the solar panel using adhesive strips to prevent stress on the wires and to make the project more aesthetically pleasing.