simple tone oscillator / 22mF capacitor

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THE_RB

Joined Feb 11, 2008
5,438
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But this dos not change the fact that this circuit will work even if you replace the speaker with a resistor. If you choose resistor wisely this circuit will work without the speaker.
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Sorry if it sounded like I was arguing with that. By correctly riding the beta and saturation curve you could get it to oscillate with a resistive load, but it's still not a great circuit.

What if PSU voltage changes and causes base current to increase? Or if someone changes the resistance of the load, or replaces the transistor with a different transistor?

Both of those circuits you just posted are proper multivibrators where each transistor turns the other transistor off. They are much better and should run well, relatively independent of PSU voltage or transistor beta.

If you added a resistor or two you could add hysteresis to the Q2 base turnon/turnoff point and make it a really reliable circuit. :)
 

WesFanMan

Joined Jan 28, 2015
1
This circuit has been written about by Forrest Mims III and is sourced from the 1964 7th edition of the GE Transistor Manual pg. 379. It is titled "Metronone". For that purpose this circuit is fine and an affordable implementation. Nice job by Jony 130 for his circuit description. But I'm not sure of his KVL V_C1 = Vcc - Vbe - Vce(sat) ≈ 8.6V.
 

alfacliff

Joined Dec 13, 2013
2,458
Some points to note:

1) 22mF is not the same as 22μF.

22mF is 0.022F
22μF is 0.000022F

2) Don't try to analyze circuits using both holes and electrons. It will only add to confusion. You can use electrons alone or conventional current alone.

3) Do not refer to transistors as a valve that "opens".
"open" in electrical terms suggests that no current flows.


You can use a single fixed resistor. The variable resistor allows you to adjust the frequency of oscillation.


The dual NPN/PNP transistor circuit is a classic oscillator.
As the capacitor charges through the resistor, the voltage at the base of the NPN transistor gradually increases until the NPN transistor conducts which also causes the PNP transistor to conduct. The capacitor dumps its charge through the NPN transistor and the cycle repeats.

22mf is the same as 22 microfarad. it is an older way of putting it. there was never any 22 milifarad caps, all were in microfarad labled mf. just like pico farad was mmf, micro micro farad.
 
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