Solder an 8-pin IC (integrated circuit) holder onto a strip-board with 10 holes to the left, 7 to the right and 1 to the top and bottom. Break the four tracks under the holder with a track cutter. Identify a 470-k, a 1-k and a 220-k resistor using color-coded stickers. Insert and solder the resistors in line with the holder. Identify a 1-microfarad 16-V radial capacitor, a colorful light emitting diode (LED), a 555 astable timer IC, a battery clip for a 9-V PP3, and a strip-board for mounting with 6 rows and 21 holes. Solder two wire links around the holder using plastic-coated single-core wire. Solder in the remaining components. Insert the 555 timer and power supply.
Perform a simple modification to a computer sound card using a unidirectional "electret" microphone, which works best. Wire a simple, one-conductor shielded cable to the connector sleeve. Connect the ring and tip to the central conductor. When the stereo "mic" input mode is selected, the bias voltage is provided for both the tip and the ring. Connect the shield of both microphones to the sleeve of the plug. Connect the left mic to the tip and the right mic to the ring.
Create a nighttime light using a simple circuit that contains a CR2032 3-V lithium coil cell, an LED, an LTR-4206E phototransistor, a 2N3904 transistor and a 1-k resistor. Use the brightest LED you can find, such as a red 60-candela bulb that casts a visible beam of about 20 feet in a well-lit room.
This simple heartbeat sensor, designed by Kristopher Dos Santos at the Massachusetts Institute of Technology, measures a child's vital heart data from inside a calming cuddly toy. A simple electrocardiogram (ECG) circuit is embedded into the toy so that the pulse sensors are in the "paws" or hands of the toy. As the child holds the toy's hands, her pulse can be monitored. Other required components include an AD623 instrumentation amplifier, a 10-nanofarad capacitor, a voltage divider, a 4.8-V power supply and two copper coins.