Once students build and test a variety of these circuits, they take a pass/fail test. They have to build and test a series-parallel circuit of their own design, diagram the circuit, test resistance, current flow, and voltage drops correctly with me watching them work. Once complete, they then begin performing tests on school vehicles using lab worksheets
to guide them. The main purposes of the circuit building are to get students used to using meters and taking measurements. A second benefit is they can see how series, parallel, and series parallel circuits operate.
Transitioning to working on a vehicle is often where a stumbling block occurs. Students who have little experience with using a DMM usually do not transition easily to making measurements on vehicles and still confuse taking a voltage reading with measuring voltage drop. Additionally, students still may not have a good grasp of how voltage drops affect circuits on the car. To help visualize an actual circuit, I put together a brake light circuit that approximates how it would be on the vehicle.
Shown in Figure 4
, the brake light circuit initially is wired up to work normally. As a class, we go through each part of the circuit, discuss the functions and operation of the components, and use a meter to make measurements. Once familiar with how the
circuit works, I introduce se
veral "bugs." Included in the bugs are damaged wires at the switch, two resistors wired in after the switch, and several poor connections at various points, shown in Figure 5
With the circuit taped to the board, students can easily visualize the circuit and then perform tests at various points to try out diagnosing and fixing various concerns. This usually starts some of the students on developing diagnostic techniques and thinking about how to find and repair electrical problems.
I've found that providing a circuit like this, and one that is removed from the car, allows students to get a much better idea of how a circuit is constructed, how it operates, and how to perform tests before being expected to tackle real problems on vehicles.
More to come next month.