Throwing light on it
The 555 IC is one of only two new types of electronic component this circuit introduces you to. The other is a light emitting diode (LED) which is a type of indicator. One is shown in Photo 5.7. LEDs are polarised and so must be inserted into circuit the right way round. All LEDs have an anode (which goes to the more positive side of the circuit) and cathode (which goes to the more negative side).
Generally, but not always, the anode and cathode of an LED are identified by the lengths of the component leads — the cathode is the shorter of the two. There’s often a flat side to an LED too — usually, but again not always, on the cathode side — to help identify leads.
Photo 5.7 One of the most popular electronic components, the LED
The complete circuit’s breadboard layout is shown in Figure 5.4. Build it and see what happens.
When you turn on, you should find that the LED flashes on and off, quite rapidly (about five or six times a second, actually). This means your circuit is working correctly. If it doesn’t work check polarity of all polarised components: the battery, IC, LED and capacitor.
Figure 5.4 The breadboard layout for the multi-vibrator circuit as shown in Figure 5.2
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