146
2.56 Sensor toggle switch (finger)
Circuit 121:
Sensor toggle switch with LED
Setup information
Install the three transistors, the diode and the six resistors as shown in
Fig. 2.121.
Finally insert the eight
jumpers and the two jumpers used as switches (shown dashed). For your guidance we have labelled the
“switches” with “Tab On” and “Tab Off” accordingly. Check the placement on the board again and only then
connect the battery.
Components required:
2 x 2N3904 transistors,
1 x 2N3906 transistor,
1 x red LED, 1 x 1 k
Ω
resistor, 1 x 10 k
Ω
resis-
tor, 1 x 47 k
Ω
resistor,
1 x 100 k
Ω
resistor,
2 x 220 k
Ω
resis-
tors, 1 x breadboard,
1 x battery, 9V battery
with clip connector
Fig. 2.121:
Sensor toggle switch
with LED
Experiment
If everything is wired correctly, both “switches” are open, which means that one end of our two jumper
wires is not connected. “Close” the jumper marked
Tab on
for a moment. The red LED is steady lit. If you
“open” the
Tab On
switch again, the diode will continue to glow. The circuit is so responsive that it is
enough to bridge the two bare wire ends of the “switch” with a grease-free finger. The red LED is accordingly
switched off again by the
Tab off
switch.
The circuit (called bistable or two-state flip-flop) will remember that at some point the
Tab off
switch was
momentarily activated. You can reset the circuit by momentarily “closing” the
Tab off
switch. In both cases,
the touch of your finger is enough. This will turn the red LED off again.
This is a fundamental building block in modern digital electronics. A bistable flip-flop stores a piece of infor-
mation for an unlimited time. It knows two stable states, namely
On
and
Off
(digital technology calls these
states
high
and
low
or
1
and
0
). Each of these states can be triggered by an external control signal. Quartz
watches, mobile phones and in particular Tablets and PCs have these basic circuits in large numbers.
The circuit diagram for this experiment is shown in Chap. 3, Fig. 3.121.
Содержание ELECTRONICS EXPERIMENTS BOX
Страница 4: ......
Страница 251: ...253 Fig 3 27 Circuit 27 4 seconds switch off delay Fig 3 28 Circuit 28 20 seconds switch off delay...
Страница 258: ...260 Fig 3 42 Circuit 42 Active 8 5V battery monitor Fig 3 43 Circuit 43 Active 7 8V battery monitor...
Страница 260: ...262 Fig 3 46 Circuit 46 Meters for 1 5 V Zener diodes and higher Fig 3 47 Circuit 47 Discreet 2 2V Zener diode...
Страница 261: ...263 Fig 3 48 Circuit 48 Discreet 2 9V Zener diode Fig 3 49 Circuit 49 Discreet 3 7V Zener diode...
Страница 265: ...267 Fig 3 56 Cir cuit 56 Audio limiter Fig 3 57 Circuit 57 Amplifier for a storm detector...
Страница 269: ...271 Fig 3 64 Circuit 64 Stabilizer for 1 9 V Fig 3 65 Circuit 65 Stabilizer for 2 5 V...
Страница 275: ...277 Fig 3 80 Circuit 80 Quiztimer 30 seconds Fig 3 81 Circuit 81 Handy diode tester...
Страница 290: ...292 Fig 3 118 Circuit 118 HF watch dog with LED indicator Fig 3 119 Circuit 119 HF watchdog with moving coil instrument...
Страница 295: ...297 Fig 3 130 Circuit 130 4 seconds switch on delay Fig 3 131 Circuit 131 15 seconds switch off delay...
Страница 298: ...300 Fig 3 136 Circuit 136 NAND gate with moving coil instrument Fig 3 137 Circuit 137 Input level Mixing console...
Страница 300: ...302 Fig 3 140 Circuit 140 Electrometer with moving coil instrument Fig 3 141 Circuit 141 Simple AM Radio...
Страница 315: ...317 Fig 3 179 Circuit 179 HF generator 150 kHz Fig 3 180 Circuit 180 HF generator 420 kHz...
Страница 324: ...326 Fig 3 202 Circuit 202 3 seconds switch on delay Fig 3 203 Circuit 203 7 seconds switch on delay...
Страница 325: ...327 Fig 3 204 Circuit 204 Piercing siren sound with Piezo element Fig 3 205 Circuit 205 Discrete Operational ampli fier...
Страница 328: ...330 Fig 3 210 Circuit 210 Discreet 5 2V Zener diode Fig 3 211 Circuit 211 Discreet 7 4V Zener diode...
