PART 4: The Annual 1 Minute Interval Timer Contest

Making a 1 Minute Timer

In this part, you will make an timer which is on for as close to 1 minute as you can. To do this you will use a potentiometer as a variable resistance that you can adjust. The controlling resistance, R, will be obtained by placing a fixed resistor in series with the potentiometer.

The potentiometer is simply an adjustable resistor as shown in Figure 33.

(a)	(b)	(c)	(d)

When the potentiometer shaft is rotated, a tap on a circular resistance moves as indicated by the schematic symbol shown in Figure 33(b). The potentiometer can be used to obtain a fraction of the voltage across its outer terminals as shown in Figure 33(c) or to achieve a variable resistance as shown in Figure 33(d). We will be using the potentiometer as a variable resistance.

The interval timer prototype board with the series resistor and potentiometer is shown in Figure 34.

(The leads missing in Part 1 are not shown in this figure either.)

Select a value for the fixed resistor and adjust the potentiometer so that the timer's time interval is as close to 1 minute as possible.

The circuit you will use must be as shown. This is identical to the interval timer you constructed in Part 1 except the single resistor in the RC timing circuit has been replaced by two resistors consisting of a fixed resistor and a 100K potentiometer in series. The potentiometer should be set so that the time interval is as close to 1 minute as possible.

Rules:

1. You must use the single turn 100K potentiometer connected in series with a fixed resistor as shown in the diagram above. You may use any appropriate value for the fixed resistor.
   

2. Immediately before testing your circuit, the potentiometer will be set to its limiting position. You will then be allowed to reposition it. (It is OK to put a mark on the potentiometer to aid you in this.)
   

3. You will be allowed only one test.
   

4. If your interval timer fails when presented for the test, you will be disqualified. (So make your prototype neat.)
   
   

Prizes will be Awarded for the Times Closest to 1 Minute

Part 4 Exercise: Finishing Up

1. Entering the Competition
   
   

   It is required that you have an entry in the "First Annual 1 Minute Interval Timer Competition".

   
   

2. The Project Report
   

   A brief project report is required. It should contain the following:
   

   • The nominal design graph (on 4 cycle loglog paper) with the plotted points from your measurement along with description of what it is and instructions on how to use it.
     

   • The completed "Analysis or Effect of Component Variations on Time Interval" sheet along with a description of what it means.
     

   • A description of your personal experiences with the project.