169
Circuit 143:
Water level alarm with moving-coil instrument
Setup information
Install the two transistors and the four resistors as shown in
Fig. 2.143.
The ten jumper wires come next.
Last but not least connect the moving-coil instrument. Check the placement on the board again and only
then connect the battery.
Components required:
2 x 2N3904 transis-
tors, 1 x 4.7 k
Ω
resis-
tor, 1 x 10 k
Ω
resistor,
2 x 220 k
Ω
resistors,
1 x moving-coil instrument,
1 x breadboard, 1 x 9V bat-
tery with clip connector
Fig. 2.143:
Water level alarm
with moving-coil instrument
Experiment
Even if everything is wired correctly, nothing will happen at first. But if you dip the two bare wire ends that
represent the sensor in water, the needle of the moving-coil instrument will deflect sharply. For example,
you could also check by means of the scale of the deflection, whether your potting soil is too dry and needs
some water, if you push the bare wire ends into the soil of a flower pot. The weaker the deflection the drier
the soil.
The circuit diagram for this experiment is shown in Chap. 3, Fig. 3.143.
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...
