# Explanation of a circuit

Discussion in 'Electronics Homework Help' started by endlessparadox, Jul 12, 2018.

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Feb 14, 2018

Need to understand simply because im pretty slow at understanding things.
First what does the 7805 do regulate voltage what it means more exactly?
UM66 how does it generate a melody does it make different tones or only one thing.
I know transistors boost current and act like amplifiers all that i know.
What is the point of a npn and pnp assigned like that.
Also why is a capacitor needed?

And you need a loudspeaker right for the um66?
A buzzer wouldnt work right?

2. ### (*steve*)¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥdModerator

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Jan 21, 2010
At the very least, that circuit is incomplete ad won't do anything useful.

Maybe the collector of the top transistor should be connected to +5V

40
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Feb 14, 2018
Still it is a circuit i got in a class.If it doesnt work :/
Do you think you could just make a general explanation?

4. ### kellys_eye

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Jun 25, 2010
Given this is a 'class work' assignment we aren't about to hand you the answers but instead we point you in the right direction in order for you to find out for yourself.

Google the data sheet for the UM66 and read about what it does, how it does it and how it is used. All the information is available in the data sheet and I think this is what your teacher is suggesting you do - LEARN. It's not the same as being TOLD.

Harald Kapp likes this.
5. ### Harald KappModeratorModerator

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Nov 17, 2011
Good point. This is our forum policy.

The 7805 is a voltage regulator. Look up its datasheet and learn how it operates.

The transistors form a very simple class B amplifier. Read and learn. However, the collector of the NPN transistor needs to be connected to a positive voltage source, cf. post #2 by Steve.

Draw schematically the output voltage at the connection of the two transistors (assume a sine wave or a square wave for simplicity, frequency is not important). You should recognize that the output voltage has two components. Tell us which these two components are. Hint: one is AC, the signal you want to hear. The other is ???
Consider the impedance of the speaker with respect to the second component. What does this mean in terms of power dissipation and operating point of the speaker? You'll have to get acquainted with the principle of operation of a dynamic speaker.

Depends on the type of 'buzzer'. The term 'buzzer' is used (unfortunately) rather indiscriminately for different types of piezoelectric sound generating devices. A simple piezoelectric speaker (without the electronics to generate a buzzing sound by its own) could be used in this circuit, depending on the frequency of the signal (every kind of speaker is optimized for a certain range of frequencies). An example for this kind of use are musical greeting cards.

6. ### WHONOES

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May 20, 2017
Could use an elctromechanical buzzer / sounder.