[...]... headphone plug is fully inserted into its socket 10 Fix the working board to the lid Use the sticky pads and apply gentle pressure Fit the tuning knob, the ON/OFF switch and the earphone socket 11 Test again If all is still working, fit the lid screws and admire your completed radio! 11 Radio and Electronics Cookbook Parts list Capacitors C1, C2 0.01 microfarad (␮F) C3, C4 0.1 microfarad (␮F) VC1 500 picofarads... Figure 1 shows the circuit diagram Figure 1 Circuit and block diagrams of the radio Description The whole circuit is built on a 50 mm by 50 mm printed circuit board (PCB) designed to fit on the inside of the lid of a plastic box, and is stuck there using sticky pads, the shaft of the variable capacitor going through a hole in 9 Radio and Electronics Cookbook Figure 2a The PCB, solder side Figure 2b The... all the same, and so present no problem They (and the resistors) may be connected either way round, unlike the two semiconductors (see later) The resistors are coded by means of coloured bands You can refer to Chapter 7 if you have difficulty remembering the colours and their values Figure 1 Terminal strip – position of components 1 Radio and Electronics Cookbook 1 2 3 4 Brown, Black, Yellow Green,... R1, R2 and C2; a voltage appears at pin 3 which ‘switches’ at this frequency between zero and a voltage close to the supply voltage, which in this case can be anywhere between 6 V and 14 V The output current, when applied through R3 to a small loudspeaker, produces an audible tone, provided that there is a DC path between the two test leads Figure 1 The circuit diagram 17 Radio and Electronics Cookbook. .. about 40 × 40 mm is sufficient to hold all the components except the potentiometer and switch (see later) The case can be plastic or aluminium, and one measuring 65 × 100 × 50 mm is about right Make sure there are holes in the case beside the speaker cone to let the sound out, and larger holes for the potentiometer and switch If a potentiometer is used with a combined ON/OFF switch, then the extra hole... plain side is the component side and the soldered side is the track side Figure 1 shows the track side full size Make the PCB from the pattern given in Figure 1 Otherwise, build the circuit on a matrix board 2 Three resistors Locate the gold or silver band around the resistor, and turn the resistor until this band is to the right There are three coloured bands at the left-hand end of the resistor Find... damp hands and the frequencies will be higher still 4 As a thermometer Connect the test leads to a thermistor (a device whose resistance changes with temperature) and warm it with a hair-dryer, or even in your hands, and you will hear the pitch changing with the temperature of the thermistor A suitable ‘bead’ thermistor is available from Maplin (order code FX21) 5 As a diode tester Use any diode, and. .. do hear, however, is a series of clicks, as the voltage across the speaker changes quickly from 0 to 9 V and back again Figure 1 The metronome circuit is rather like the Morse oscillator 21 Radio and Electronics Cookbook Figure 2 The component wires are pushed through holes in the circuit board and joined together underneath Variation of speed could be achieved by varying resistance or capacitance... which) Solder one end of the resistor to the vacated speaker tab, and the free speaker lead to the other end of the resistor This will limit the volume of sound from the speaker, and lengthen the life of your battery If it is still too loud, try a resistor of a larger value, or use a smaller resistor to make it louder 15 Radio and Electronics Cookbook Parts list Resistors: all 0.25 watt, 5% tolerance R1... R1 10 kilohms (k⍀) VR1 47 kilohms (k⍀) linear potentiometer Capacitor C1 33 microfarads (␮F) electrolytic Transistors TR1 2N3053 TR2 2N2905 npn pnp Additional items S1 SPST ON/OFF switch LS 3 ohms (⍀) loudspeaker Knob with pointer for VR1 PP3 battery and connector Aluminium case, 65 × 100 × 50 mm Matrix board (plain), 40 × 40 mm 23 Radio and Electronics Cookbook 7 What is a resistor? Introduction Materials .