2. Adding a switch
Step 2 of the automatic light: SW1 goes between B1 + and R1. Off: the LED is dark and no current flows. Component 2 of 14: the switch. A switch is a deliberate break in the circuit. SPST (one pole, one throw) just opens or closes one wire. It goes in the + supply line, before everything else, so that when it is off nothing downstream is live.
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Parts list
Test procedure
Each test has an expected value and a pass range, like a factory test sheet:
- Switch on: LED lit
- Switch off: no current
How it works
The switch. A switch is a deliberate break in the circuit. SPST (one pole, one throw) just opens or closes one wire. It goes in the + supply line, before everything else, so that when it is off nothing downstream is live.
Reading it. Ratings are printed or moulded on it: current and voltage (e.g. 6 A 125 V AC). A switch rated for AC can carry less DC (the arc does not go out by itself), so check the DC rating for battery work.
Testing it. Meter on continuity: beeps when on, silent when off. In circuit, with the switch off you should read the full supply across its two terminals; with it on, almost zero.
In the build. SW1 goes between B1 + and R1. Off: the LED is dark and no current flows.
Builds on lesson 1: everything from before is still there.
Next: lesson 3, potentiometer.
Things to try
- Click SW1 to switch it off and on.
- Put the meter (V) across SW1 while it is off: you see the whole 9 V across the gap.
Background
One circuit, built up one part at a time: by lesson 14 it is a solar-powered, dusk-sensing, motion-triggered timed lamp with an alarm.