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A Solar-Powered Lighting System, Pt.2

Last month we described the operation of our new off-grid lighting system, featuring free power courtesy of the sun! Now we move on to the fun part: building it!

Part 2 - By John Clarke

We’re confident that this will be a very popular project, offering far more features than typical “solar chargers”.

One thing we didn’t mention last month is that being all low-voltage, it would make a perfect school electronics project. And the fact that it is decidedly “green” will bring a warm glow to any environmentalist teacher’s heart!

Click for larger image
Same-size photo of the completed PC board. As you can see here, both the LDR and LED can be mounted on the board (the LDR via CON2) and bent over 90° to line up with holes in the case.
Click for larger image
Fig.6 matches this photo and shows the component overlay together with the connections to the solar panel, SLA battery, PIR, LEDs and manual switch.

To fully understand the project, you will need to refer to the detailed explanation given in Part 1 (May). It also contains the circuit diagram which you might need to refer to during construction.

The controller is built on a PC board coded 16105101, measuring 133 x 86mm. This PC board is designed to be housed in a 157 x 95 x 53mm utility box (size UB1), clipping into the integral mounting slots moulded in the side of the case.

Begin construction by checking the PC board for breaks in tracks or shorts between tracks and pads. Repair if necessary. Next, check the hole sizes are correct for each component. The screw terminal holes are 1.25mm in diameter compared to the 0.9mm holes for the ICs, resistors and diodes.

Assembly can begin by inserting the links and the smaller resistors. When inserting the resistors, use the resistor colour code table to help in reading the resistor values. A digital multimeter can also be used to confirm the values, especially where close colours might be misleading. We used tinned copper wire for the links although 0Ω resistors may be supplied in kits. These look like small resistors but have just one black stripe around their body.

As mentioned last month, resistor R2 (100kΩ) is only installed if a standard PIR detector is to be used. It is left out if the recommended (Altronics) PIR is used.

Next are the diodes, mounted with the orientation as shown on the overlay. Don’t mix up the Zener diodes and ordinary diodes. Now is a logical time to solder in the PC stakes and the 3-way headers for LK1 and LK2 and 2-way pin header for TP3 and TP4.

IC1 is mounted on a DIP18 IC socket. Solder in the socket (with the notch in the direction shown) but at this stage, don’t plug in the IC: it’s left out until the 5V supply is adjusted. The remaining ICs can either be mounted using sockets or mounted directly on the PC board. Ensure each IC is placed in its correct position and is oriented correctly, with the notch (or pin 1 indicating dot oriented) as shown.

When you solder the fuse clips in, you’ll see they have an end stop or small lugs to prevent the fuse sliding out. The lugs need to be to the outer ends of the fuse – if soldered in back to front the fuse won’t go in.

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