The Junior Computer as a frequency counter

5-26 - elektor may 1982 the Junior Computer as a frequency counter radio. It is more convenient to inter- connect the components directly. Figure 3 shows one method for this. The "chassis" is made of plastic having the same dimensions as the "tray" of a matchbox. The variable capacitor is mounted onto the chassis by means of appropriate screws. The ferrite rod is attached by glueing each end to the lides of the chassis. A standard earphone socket is used. Normally the switch part acts to isolate the loudspeaker, but in this case it is utilised as a battery connection. The moving contact part of the switch is cut off with pliers or a wire cutter to leave only the fixed terminal. This serves as the positive contact for the battery. A smal) brass plate (glued to the side of the chassis) serves as the negative con- tact. The position of the socket is determined by the size (width) of the battery. Note that an on/off switch is not necess- ary when constructing the circuit as in figur...