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Mini Metronome


mastrila
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I would like to build the "Mini Metronome" for my daughter.
Sure I could buy one but what's the fun (Besides, I do like to impress my kids).
The instructions specify that SW1 needs to be "ganged" with P1. Can somebody please explain what this means and how to do it?
I plan to replace Q3 (hard to find in Canada) with an N-Mosfet. Any thoughts?
Thanks in advance,
                              Mastrila

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Hi Mastrila,
This project? http://www.electronics-lab.com/projects/oscillators_timers/009/index.html

A switch that is "ganged" with P1 is the pot with a built-in switch that turns off the project when you turn it all the way down. Use a separate on-off switch if you want.

An N-channel Mosfet can't replace a PNP transistor but a P-channel one can.
I can't see how the circuit can work with a PNP transistor, even the "special" one, because the circuit doesnt provide enough base current through R7 for it and the output voltage of an ordinary 555 timer doesn't go high enough to turn it off.

Therefore I would use a P-channel Mosfet for Q3 or add a 1k resistor as in my sketch and use a common TIP115 darlington power transistor for Q3.
Also, I would use a 9V battery because with 12V it would probably blow you and the little speaker away. ;D

post-1706-14279142533088_thumb.png

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