Make Your Own Low-Power AM Radio Transmitter
Materials and Equipment
Supplies for this project are available in one convenient kit from the Science Buddies Store To do this experiment you will need the following materials and equipment: * Crystal oscillators (2), notes:
* Each oscillator should be at a different frequency, within the AM broadcast band (0.53 to 1.71 MHz in North America, 0.53 to 1.61 MHz elsewhere). * For use with the solderless breadboard in this project, you want the 'full can' package. * Solderless breadboard
* 1000 ohm to 8 ohm audio transformer
* 1/8 inch mono phone plug
* 6 V AA battery holder (holds four batteries),
* 1.5 V AA batteries (4)
* Alligator jumpers
* Jumper wires for breadboard.
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Building the Circuit
Before we get into the step-by-step instructions for building the circuit, we'll first go over the circuit design and show you how the solderless breadboard works. Figure 2, below, shows the connections you need to make to build the circuit. The transformer isolates the music player from the rest of the circuit, couples the music player and the crystal oscillatory, and "steps up" the signal voltage from the music player in proportion to the ratio of 1 kohm to 8 ohms. The stepped up signal from the secondary coil of the transformer modulates the power to the oscillator chip (+ power at pin 14 and − power at pin 7). A wire connected to the oscillator output (pin 8) serves as the antenna for broadcasting the amplitude-modulated radio wave.
Figure 2. Simple AM transmitter circuit diagram. The square corner of the oscillator corresponds to pin 1. The pins are numbered according to standard positions for a 14-pin integrated circuit.
| Figure 3, below shows a small breadboard. The breadboard has a series of holes, each containing an electrical contact. Holes in the same column (examples highlighted in yellow and green) are electrically connected. When you insert wires into the holes in the same column, the wires are electrically connected. The gap (highlighted in orange) marks a boundary between the electrical connections. A wire inserted in one of the green holes would not be connected to a wire inserted in one of the yellow holes. Integrated circuits, such as the oscillator used in this project, should be inserted so that they span the gap in the breadboard. That way, the top row of pins is connected to one set of holes, and the bottom row of pins is connected to another set of holes. If the integrated circuit was not spanning a gap in the breadboard, the pins from the two rows would be connected together (shorted), and the integrated circuit wouldn't work. Finally, the two single rows of holes at the top and bottom (highlighted in red and blue) are power buses. All of the red holes are electrically connected and all of the blue holes are electrically connected. These come in handy for more complicated circuits with multiple components that need to be connected to the power supply. If you have never...
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