Huh? It's amplifying the signal right?
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"The 555 can be used as an amplifier. It operates very similar to pulse-width modulation. The component values cause the 555 to oscillate at approx 66kHz and the speaker does not respond to this high frequency. Instead it responds to the average CD value of the modulated output and demonstrates the concept of pulse-width modulation. The chip gets very hot and is only for brief demonstrations."
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Wow, that is a very crude way of doing that.
Still not entirely sure how it works!
How's pin 5 which is hooked up to the transistor create any amplification?
What's inside...
I see... it's the input reference pin on the opamp!
interesting use then....
cjdelphi:
Huh? It's amplifying the signal right?
The rightmost electrolytic capacitor shorting out the speaker is nonsense. Get rid of it,
add a 330uF decoupling capacitor between supply rail and ground (always a good
idea with a 555 which is very noisy). The 10uF capacitor in series with the speaker can
be a lot larger in value, 1000uF perhaps.
I am also worried by the lack of load resistor from the transistor collector to the supply...
Hi guys, the circuit is as johnwasser has said, he even supplies the reference link.
Don't try to change the electro caps around the speaker. They and the low impedance of the speaker provide some filtering even though its running at 66kHz.
A 330uF would be a good idea, especially if you are using a battery supply.
The PWM occurs because pin 5 is connected to part of the resistor chain that provides the 1/3 and 2/3 ref voltages that the timer uses in producing the duty of the signal produced.
The transistor does not require a collector resistor because it is supplied by the internal resistor chain.
Tom
This circuit is far from ideal. With both capacitors, you've made a low impedance path to ground.
At 66kHz, a 10uF capacitor has an impedance of only about 0.24 ohms. So a 330uF cap is entirely unnecessary.
So insert an inductor -after- the first 10uF cap, then to the speaker, and then the other 10uF cap can remain across the speaker. A 100uH inductor would be about 41.5 ohms at 66kHz, go with that.
This 555 circuit acts as a crude PWM. Really crude. The frequency changes along with the duty cycle, and not very linearly. There are much better ways to do this, I have built a Class D amplifier with 555 timers before.
That internal block diagram has a mistake. Pin 5, the Control Voltage pin, should be connected to the junction of the top and middle 5k resistors, in addition to being connected to the inverting input of the upper comparator.
