for the circuit in the pic can I use BC547 instead of TIP31
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First of all I hope you mean BC547 and not BC457 because a BC457 is a crystal oscillator. Then again TIP31 is a 3 amp and BC547 is a 100 mill amp which should handle the 20 to 30 mill amp of the LEDs however at best the speaker will only work as a buzzer. You can find the datasheets at these two sights. http://www.maxim4u.com/ http://www.alldatasheet.com/ I find this sight great for parts, free datasheets, and hard to beat prices. http://ca.mouser.com/search/Default.aspx Joe
Not unless you put two into a Darlington connection.