2 transistor easy to make function generator usable from 75 Hertz to say 20 KC schematic and demo



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Please read the description/textbox first. Easy to make 2 transistor function generator (measurement instrument & driver) working between 75 Hertz and (say) 20 KC (20 KC with 2 x a 4N7 cap on 24/28 Volt). Corrections to this video: below in the textbox.

First (older, 13 june 2022, few days ago) video is here https://youtu.be/LMWH-OinNcg

That (24 V/28V) is a somewhat higher voltage, the voltage must be adaptable (read variable, with a potentiometer or so, the circuit does not take much current) to make the frequency variable, in combination with the capacitors value. Easy to realize. More info in the video.

Waveform is somewhat adaptable (more in the video).

Frequency is set via the supply voltage (9-24/28 V) & the capacitance, given by the value of the used 2 capacitors, nonpolar types by the way.

Thus: the output frequency is set by the value of the two used capacitors. Say with 2 capacitors of 1.5 uF (bipolar, referred), we are on (say) 100 Hertz or say in the 100 Hertz range.

But with 2 capacitors of 4N7 (4700 pF) at voltage “X” (= say 24 Volt or 28 Volt) we are on 20 KC.

Take e.g. a double or single switch with 1 mother contract and 5 or more “switch-to” contacts, so that you can "switch in" different capacitor values (4N7-10N-50N-100N - 1 uF all nonpolar).

With lifting up the supply voltage (9 V-24/28 Volt) and making it variable between 9 V and say 28 Volt (the maximum that this electronic circuit can handle = 28 Volts) you can surely find (read: align to) the frequency that you want/need. And thus making it (this circuit) usable a test instrument.

Frequency setting can be done with a 10K potentiometer, for safety reasons: connect to the (+) of the top electrode of that 10 K potmeter (going to the + 28 Volts) a series resistor of (say) 1K (=1000 Ohm). Connect the wiper of that 10 K potm. to the circuit and the other potm. electrode to the minus. Then you have a variable voltage divider, read a variable voltage supply to feed this circuit.

So this is the easiest way to make a simple and properly working function generator, usable to test all kinds of circuits (say audio), or to drive transistor circuits etc.

The pulse-pause ratio (the duty cycle) can be set/aligned/to different states by (say) taking different values for the 2 capacitors that set the time dependancy, say e.g. 10 N and 100 N, the duty cycle will change substantially. Or 4N7 and 100 N. Test/Try/Experiment....Always good!

CORRECTIONS to the video: on 1.35 I talk about the “potentiometer of 10 K”, but of course I mean the fixed value resistor of 10 K. On 9.07 I say that the frequency drops to a lower level, but not only that: the waveform changes somewhat (oscilloscope views).

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