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Shopping List

The easiest way to obtain parts for the nine experiments in this workshop is by ordering a kit. You can order your Easy Electronics kit and handbook bundle (including three additional experiments) from Maker Shed.

If you prefer to shop for parts individually online, I suggest sites such as ebay.com, mouser.com, digikey.com, or newark.com.

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Here’s a complete list of everything you need for the 9 experiments in this workshop.

Batteries

Alkaline AA size.

Quantity: 3.

Note: Do not use lithium batteries!

Battery Holder for Single AA Battery

With solder pins or PCB terminals. Eagle Plastic Devices part 12BH311P-GR or similar.

Quantity: 3

Battery Holder for Three AA Batteries

With solder pins or PCB terminals. Eagle Plastic Devices part 12BH331P-GR or similar.

Quantity: 2.

Miniature Incandescent Light Bulb

This item is sometimes sold as a “lamp”. The one that I prefer, pictured throughout this book, is rated for 5V and 60mA and has a ceramic base with two short leads. Search for JKL 7361 by JKL components, or CM7361 by Chicago Miniature Lighting, a subsidiary of VCC. If these options are unavailable, a very similar bulb is JKL 7362; it will use more current and will be a bit dim when used with a series resistor, but should work in the experiments. Another option is to use a 6V bulb rated for 40mA or 60mA; these usually have a size E10 screw-thread base, and require a matching socket. Search online for E10 6V bulb, and you will find scientific supply companies selling the bulb and socket for high-school electrical experiments. It may be less bright than an equivalent 5V bulb, but should work.

Quantity: 2.

Alligator Jumper Wire

Single wire with alligator clip at each end. Any length, but very short ones are more convenient (3" to 6").

Quantity: 2 red, 2 black, 3 green.

Slide Switch

Also known as a slider switch. To use it with alligator clips, it should be as large as possible, with pins widely spaced. This can be a problem, as most slide switches today are subminiature. I suggest that the minimum body size is 1/2" or 13mm long, minimum pin spacing 1/8" or 5mm. You want a single-pole, double-throw switch, which may be identified as SPDT, SP2T, 1P2T, or PDT. Examples of an acceptable switch are part number PM13B012 by Apem or L102011MS02Q by C&K Components. You will be switching very small currents at only 4.5V, so you do not need to be concerned about maximum voltage or amperage listed for a switch.

Quantity: 1.

Resistors, Quarter-watt, 5% or 10% Tolerance

You will need values 33 ohms, 1K, 10K, and 100K: 2 of each. Values 2.2K and 3.3K: 1 of each.

Transistor, 2N3904 NPN Bipolar

Purchase from any manufacturer.

Quantity: 2.

LED

Low-current type, tinted red. Avago or Broadcom HLMP-D150, or HLMP-D155, or HLMP K-150, or HLMP K-155, for a typical 1.6V forward voltage, 20mA maximum average current but able to respond to 1mA.

Quantity: 2.

Phototransistor

Lite-On LTR-301 preferred, side-facing NPN type, rated 5V. Alternatively Optek / TT Electronics OP550B. (The O at the beginning of this part number is letter O, the 0 near the end is numeral zero.) The component that you use must be able to pass a constant current of 3mA. If you find that a side-looking phototransistor has both leads of equal length, hold the component with the lens facing you and the leads pointing down, and the right-hand lead is probably the collector (more positive). If in doubt, apply power very briefly.

Quantity: 1.

Capacitors, Electrolytic

Rated 10V or higher. 1µF, 10µF, 100µF, and 470µF.

Quantity: 1 of each.

Capacitors, Ceramic

2.2nF, 10nF, and 100nF. (These values may be written as 0.0022µF, 0.01µF, and 0.1µF.)

Quantity: 1 of each.

7555 Timer Chip

Preferred manufacturer is Intersil. If you try using a 555 timer chip, it will consume more current and may not work well at the low voltage in the experiments in this book.

Quantity: 1.

Mini Breadboard

17 rows of holes or more.

Quantity: 1.

Jumper Wires

22-gauge, stripped at both ends, in colors red, green, and black.

Length of insulation 1/2": 3 of each color.

Length of insulation 1": 2 of each color.

Piezoelectric Audio Transducer

With wire leads, DB Unlimited TP244003-1 preferred. Alternatively, CPE-827 from CUI Inc. If you search online, note that piezo is often used as the abbreviation for piezoelectric, and you should search for “piezo speakers” to avoid finding other kinds of transducers, some of which work like microphones. If making a substitution, larger is better (minimum diameter 1" or 25mm).

Quantity: 1.

Optional Items

Laser Pen

Used for triggering phototransistor.

Quantity: 1.

Magnifying Lens

Useful for reading part numbers).

Quantity: 1.

Nail Clippers

Used for trimming unruly component leads.

Quantity: 1.

Wire Strippers

For if you’d rather make your own jumper wires.

Quantity: 1.

Credits + Acknowledgements

Workshop author image
Charles Platt Author

Charles Platt is a contributing editor to Make: magazine and author of the bestselling book Make: Electronics. Formerly he was a senior writer at Wired magazine.

Explore all of Charles’s books here at Platt Electronics.

Lesson credit image

Hands-on learning for Makers.


This workshop is adapted from the Easy Electronics book and kit available from Maker Shed.

LESSON 6

Seeing Light

A phototransistor works like a regular transistor, except that it has no electrical connection to its base. The base is controlled by light instead of electricity. You’re going to see how the phototransistor can turn an LED on and off.

Supplies

  • 1 Red LED, Low-Current
  • 1 Phototransistor
  • 1 1K Resistor
  • 3 Alkaline AA Batteries
  • 1 Three Battery Holder
  • 1 Miniature 5-volt Light Bulb
  • 1 Red Alligator Wire
  • 1 Black Alligator Wire
  • 2 Green Alligator Wires

Experiment 6: Seeing Light

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Many phototransistors look like LEDs. That can be confusing, so I chose one that looks as different from an LED as possible. It’s a side-facing phototransistor. The bump is a lens that must point at a light source.

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A phototransistor has polarity. In this case, the long lead must be more positive than the short lead. (Some phototransistors are the other way around.)

Hook up this circuit, using the same 1K resistor that you used before (brown, black, red).

Cover the phototransistor to shield it from light. The LED remains dark.

Shine a strong light on the phototransistor, and the LED comes on!

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PRO TIP

Keep the Current Low

Some LEDs would overload the phototransistor in this circuit. You need the low-current kind of LED recommended in the Shopping List (it's also provided in the kit).

THINK ON THIS

How Did It Work?

A phototransistor is a semiconductor, so its resistance varies.

Light falling on the phototransistor forces its resistance low. This allows enough current to light the LED.

When you protect the phototransistor from light, its resistance rises very high. This cuts off the current.

The 1K resistor is included to limit the amount of current flowing through the phototransistor and the LED. Neither of them is designed to pass a lot of current.

If necessary, point a brighter light at the phototransistor. A laser pen or laser cat toy is ideal. You can also try using a 2.2K resistor (red, red, red) or a 3.3K resistor (orange, orange, red) instead of the 1K resistor (brown, black, red).

Concept for a Project

Suppose you mount the phototransistor in a little cardboard tube, to protect it from light, but you put a laser pen about three feet away, pointing directly into the end of the tube. If someone walks through the laser beam, the phototransistor sends a signal down a long wire to sound an alarm of some kind. This is a very simple intrusion alarm (which you can build in Experiment 12, if you've bought the Easy Electronics handbook).


Up Next!

Comprehending Capacitors