CHAPTER 11
Power On!
Building and Testing a Power Indicator Circuit
Nearly all robots need a power indicator light. It’s a very simple circuit to build.
In this chapter, you’re going to make a power indicator using the parts and tools you’ve read about in
the previous chapters. You’ll learn a little about the role of each component and how to use the multimeter
to test that the circuit is working as designed.
A circuit description generally includes a parts list, schematic, and wiring diagram, as well as
photographs and step-by-step building instructions. As you gain experience, you’ll discover that all circuits
reuse common techniques and patterns, so their accompanying documentation mostly focuses on the core
concepts or tricky portions.
Introducing the Parts List
A parts list is a brief description of each of the components that are in a circuit. Sometimes tools will be
mentioned in a parts list, but usually not. Small circuits typically don’t include parts lists, as the illustration
or diagram of the circuit provides enough information to figure out the required inventory.
Here’s the parts list for the power indicator circuit:
- Multimeter for testing
- 9 V battery, preferably rechargeable
- Three alligator clip jumper leads, preferably red, green, and black
- 1 kW resistor (brown, black, red, and gold color-code bands)
- Red LED
Testing the Parts Before Assembly
Before building, be sure to test all of your parts with a multimeter. This isn’t vital when you’re connecting
stuff together temporarily with alligator clips. However, it’s sensible to test each part if you’re going to
permanently solder them, especially if any expensive parts are involved.
From the prior chapters, you know how to use your multimeter to test for the following requirements:
- The battery’s voltage should be between 7 V and 10 V. A reading of 9 V is optimal.
- The alligator jumpers should have less than 1 W resistance (good continuity).
- The 1 kW resistor should be between 950 W and 1050 W.
- The red LED should have a voltage drop between 1.4 V and 2.0 V.