Make Electronics

Experiment 33: Moving in Steps

284 Chapter 5

theory

Calculating voltage drop    (continued)

This table shows the percent voltage lost in a circuit with 10-foot wire at 12 volts.

Wire

Gauge

Amperes

1 2 3 4 5 6 7 8 9 10

10 0.08 0.17 0.25 0.33 0.42 0.50 0.58 0.67 0.75 0.83

12 0.13 0.27 0.40 0.53 0.66 0.80 0.93 1.1 1.2 1.3

14 0.21 0.42 0.63 0.84 1.1 1.3 1.4 1.5 1.9 2.1

16 0.33 0.67 1.0 1.3 1.7 2.0 2.3 2.7 3.0 3.4

18 0.53 1.1 1.6 2.1 2.7 3.2 3.7 4.3 4.8 5.3

20 0.85 1.7 2.6 3.4 4.3 5.1 6.0 6.8 7.7 8.5

22 1.3 2.7 4.0 5.4 6.7 8.1 9.4 11 12 13

24 2.1 4.3 6.4 8.6 11 13 15 17 19 21

26 3.4 6.8 10 14 17 20 24 27 31 34

28 5.4 11 16 22 27 32 38 43 49 54

30 8.6 17 26 34 43 52 60 69 77 86

Remember, though, that the wire resistance will be higher if you are using stranded copper wire or tinned copper wire, and

this will increase the percentage of voltage lost.

Experiment 33: Moving in Steps

Time now to build something more sophisticated: a cart that orients itself to-

ward a light source. I’m going to tell you all you need to get started on this

project, but this time I won’t go all the way to the end in exhaustive detail. I

want you to get into the habit of figuring out the details, improving on plans,

and eventually inventing things for yourself.

You will need:

• 555 timers. Quantity: 8.


• Trimmer potentiometer, 2K linear. Quantity: 2.


• LEDs. Quantity: 4. If you get tired of using series resistors to protect LEDs in
  a 12-volt circuit, consider buying 12-volt LEDs such as Chicago Miniature
  606-4302H1-12V, which contain their own resistors built in. However, the
  schematic in Figure 5-108 assumes that you will use regular 2V or 2.5V LEDs.


• Stepper motor: Unipolar, four-phase, 12-volt. Parallax 27964 or similar,
  consuming 100mA maximum. Quantity: 2.


• Photoresistors, ideally 500 to 3,000Ω range. Quantity: 2.