170
2.68 Telephone monitor
Circuit 144:
Telephone monitor for analogue telephone systems
Setup information
Install the transistor, the four diodes, the six resistors and the two electrolytic capacitors as shown in
Fig. 2.144.
The thirteen jumper wires come next. Check the placement on the board again and only then
connect the battery.
Components required:
1 x 2N3904 transis-
tor, 2 x 1N4148 silicon
diodes, 2 x red LED,
1 x 1 k
Ω
resistor,
3 x 10 k
Ω
resistors,
2 x 22 k
Ω
resistors,
2 x 10 μF electro-
lytic capacitors,
1 x breadboard, 1 x 9V
battery with clip con-
nector
Fig. 2.144:
Telephone moni-
tor for analogue telephone
systems
Experiment
Even if everything is wired correctly, nothing will happen at first. But when you connect the circuit to the
analogue telephone network and a call is made, the red LED will go on. This signals that there is call.
The circuit diagram for this experiment is shown in Chap. 3, Fig. 3.144.
Summary of Contents for ELECTRONICS EXPERIMENTS BOX
Page 4: ......
Page 265: ...267 Fig 3 56 Cir cuit 56 Audio limiter Fig 3 57 Circuit 57 Amplifier for a storm detector...
Page 269: ...271 Fig 3 64 Circuit 64 Stabilizer for 1 9 V Fig 3 65 Circuit 65 Stabilizer for 2 5 V...
Page 275: ...277 Fig 3 80 Circuit 80 Quiztimer 30 seconds Fig 3 81 Circuit 81 Handy diode tester...
Page 315: ...317 Fig 3 179 Circuit 179 HF generator 150 kHz Fig 3 180 Circuit 180 HF generator 420 kHz...
