P1 is of experimental value. Start with 220 Ohms or so and modify to suit your needs. The transistor is a general
purpose kind and is not critical, almost any PNP type will work. L1 is a bell-transformer which is usually already
present in the house. If you wish, you could use a battery instead of the bell transformer. Just hookup a 9-volt
battery (or wall adapter)to points 'A' and 'B' (A=+) the diode (D1) is to protect the circuit from accidental polarity
reversal and is optional, but required as a rectifier for use with the bell transformer.
T1 is a General Purpose PNP transistor and probably anything will work. L2 comes out of an old am transistor radio.
They look like miniature transformers and are usually colored red or green. You have to fiddle with different
transformers as the sound can vary depending on the value.
The loudspeaker is a 8 Ohm type and must be larger than 200milli-Watt. I used a 2Watt type, but anything over 0.2W
will do. It really sounds like a bird and when you release the doorbell button the sound slowly fades away. I have
used this circuit in my house for over 20 years and even build the "Birdie" for others. Although an old circuit, the
experimentation and the final results still give a punch. Remember to Have fun!
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Copyright © 1993 - Tony van Roon