Project Build Your Own Solar Powered Torch

You will need

• 1x AA 600 mAh NiCad battery

• 1N5817 Zener diode

10 k )4W carbon film resistor 560 R /4 W carbon film resistor 2x 3.3 R /4 W carbon film resistor C9013 NPN transistor C9014 NPN transistor C9015 PNP transistor 300 pF ceramic capacitor 100 nF ceramic capacitor

• 1 nF ceramic capacitor

In lists of made-up useless things, solar-powered torches seem to come out somewhere at the top. After all, what use is there for something that produces light that is powered by light? Until you realize that we can use batteries to store the energy—this is a crucial leap in understanding! Now doesn't the solar torch seem so much more interesting?

A solar torch is a useful thing to build and then leave on a sunny window sill. In the event of a power cut, you know that you can go to your trusty solar torch to provide a (somewhat modest) amount of illumination!

Figures 13-9 and 13-10 show a solar-powered torch and the solar torch in its packaging. One of the things you need to think about if you are going to house your project in a round torch case, is that you will need to ensure that either:

• The torch is weighted so that it rolls in such a way that the solar cell points upwards.

• There is a flat machined into the case, which ensures that the solar cell points upwards when the flat in the case rests on a level surface.

Tragedy would strike if your solar torch were to roll over so that the flat faced away from the ground—blocking sunlight to the solar cell!

The circuit is shown in Figure 13-11. It is a variation of the outdoor solar light circuit (which you will see later in this chapter), where a pair of resistors and a switch are used to mimic the action

Figure 13-10 Solar-powered torch in its packaging.

of the photocell. It allows manual control of the LEDs and economizes by only using a single battery.

Solar Powered Torch Circuit
Figure 13-11 Solar-powered torch schematic.

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Project 36: Build Your Own Solar-Powered

Warning Light

You will need

Capacitor 0.1 F, 5.5 V Capacitor 100 |F Capacitor 6.8 |F 2 x resistors 100 k 2 x resistors 100 ohms PNP transistor NPN transistor 2 x diodes 1N4148 Super-high brightness red LED 100 |H inductor 4 x small solar cells

Tools

• Soldering iron

There are many applications where it is useful to have some sort of warning light, strobe, or beacon.

Often, the place where you want to position the warning light or strobe is totally remote from any source of power. Although we can often run things from batteries, sometimes we want to put a light where changing a battery would be undesirable. Solar energy, as well as producing clean renewable energy, also allows us to power things in remote places that would not easily be accessible using conventional cables, or where changing a battery could present a problem.

In Figure 13-12 we see a commercially available solar waterproof warning light, there are many applications for this—you might want to strap it to your back while cycling, for instance.

The beacon has a couple of modes. When the beacon is set to off, the solar cell will charge the battery; however, the light will not flash under any circumstances. In "solar" mode, the beacon will charge during the day, and when the circuit senses a low lighting condition, the beacon will begin to flash using the power stored in the rechargeable battery. Set to "on" the beacon will flash regardless

Battery Operated Beacon Light

Figure 13-12 Solar waterproof warning light.

of whether it is light or dark—however, bear in mind that this will drain the battery.

If you are going to use this beacon outside all of the time, you might want to think about how you can protect the circuit (Figure 13-13) against the ingress of water and solid matter. Most suppliers of cases sell a range of decent waterproof cases that are eminently suitable for outdoor use, or you may find that you can improvise with a Tupperware or similar container to produce a satisfactory housing.

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Figure 13-12 Solar waterproof warning light.

Strobe Light Schematic
Figure 13-13 Solar waterproof warning light schematic.

Project 37: Build Your Own Solar-Powered Garden Light

You will need

• 1N5817 Zener diode

2 x 3.3 R /4 W carbon film resistor

C9013 NPN transistor

C9014 NPN transistor

C9015 PNP transistor

300 pF ceramic capacitor

100 nF ceramic capacitor

1 nF ceramic capacitor 82 ||H inductor

CdS photocell 47 k @ 10 lux

2 x LEDs

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Tools

• Soldering iron

Solar-powered path lights (Figure 13-14) are becoming ubiquitous in just about every garden center nowadays! There are lots of advantages to using solar power rather than a hard-wired system. First of all, as a hard-wired system is exposed to the elements, you need to ensure that you use low-voltage fixtures and fittings, which require a transformer to step down the voltage, or failing that, really expensive mains fixtures and fittings. Then the next thing to consider is that even the safest low-voltage system is still vulnerable to the gardener's spade—a badly placed spade can mean disconnection of your garden lighting system.

Solar-powered garden lights have none of these disadvantages. They charge their batteries during the day, and then at night as the light fades, they switch on, providing illumination.

The change in illumination is detected by a CdS photocell.

We will be using LEDs for this project (Figure 13-15) as they provide good efficiency—a decent amount of illumination for the relatively small amount of energy we are able to provide.

Msp430 Solar Schematic Garden Light
C9015 Transistor
Figure 13-15 Solar garden light schematic.
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