It would seem that in almost all circuits the transistor is the key element and few logical circuits can do without it. Now we will present to your attention a number of extremely simple and interesting electronic circuits that lack not only transistors, but also microcircuits.
Converter for 220 V from 9 V batteries
You will need: Transformer 220 V - 12 V, it can be taken from an old music center. A motor from any toy. LED lamp 220 V. Battery 9 V.
We make a converter: We solder the output of the network winding to the light bulb. We connect one end of the low-voltage winding to one pole of the battery, and the other to the other, but in series through the motor. Polarity doesn't matter.
The light comes on immediately and the converter is working. The principle of operation is very simple: while the engine is running in its armature commutator brushes, the winding is alternately connected and disconnected. These pulses go to a transformer, resulting in a transformation.
Proximity sensor
This device reacts to the approach of objects and makes a sound and lights up Light-emitting diode.
You will need: buzzer, Light-emitting diode, infrared Light-emitting diode, phototransistor.
The scheme is very simple. We assemble everything on a universal board.
Let's check. Initially only infrared lights up Light-emitting diode, but its glow is not visible to the naked eye.
As soon as an object appears in front of the device, the buzzer beeps and the red light turns on. Light-emitting diode.
This happens because the light from the infrared LED is reflected from the object and hits the phototransistor.
LED voltmeter or level indicator
Such an indicator can be connected either to a speaker or to measure voltage in the range of 2-12 V.
The LEDs each play the role of a threshold element, so they will not pass current until they themselves light up with a bias difference between them.
Let's check.
Speaker - generator, alternative energy flashlight
A regular dynamic head is an excellent generator. If you move its diffuser quickly, the output voltage will be sufficient to light the LED.
So, we take two 4700 uF 10 V capacitors and connect them in parallel. On one side we solder the LED through a 1 kOhm resistor, on the other side we solder the diode.
We connect the output from the speaker.
We quickly knock on the speaker with our hand and see how the LED lights up, which means the capacitors are charged.
After this you don't have to knock anymore. The charge of the condensers is enough for about 2 minutes of continuous lighting of the LED.
Watch the video
Watch craft number 5 in the video:
