Construction

CHAPTER 4: LEDs 65

Figure 4-12 The LED constant current driver

You will need to solder lengths of solid-core wire to the LED’s terminals so it can plug into the breadboard. It is a good idea to leave the insulation on so there is no chance of the bare wires touching the heat sink and shorting.

Figure 4-13 Emergency LED lighting

Construction

We will use this to make a little emergency lantern by hacking a battery clip to build the electronics on top of it so it can be clipped on top of a PP3 battery in the event of a power failure (Figure 4-13).

Figures 4-14a thru 4-14d shows the stages involved in soldering this up.

First, remove the plastic from the back of the battery clip using a craft knife. Then, unsolder the exposed leads (Figure 4-14a).

The next step (Figure 4-14b) is to solder the Input lead of the LM317 to the positive terminal of the battery clip. Remember that the positive connector on the clip will be the opposite of the connector on the battery itself, so the positive connector on the clip is the socket-shaped connector. Gently bend the leads of the LM317 apart a little to make this easier.

Now solder the LED in place making sure the cathode of the LED goes to the negative connection on the battery clip (Figure 4-14c).