17-11-2012, 06:10 PM
IC UM66:
IC UM66.docx (Size: 144.53 KB / Downloads: 43)
IC UM66.docx (Size: 144.53 KB / Downloads: 43)
UM66T is a melody integrated circuit. It is designed for use in bells, telephones, toys etc. It has an inbuilt tone and a beat generator. The tone generator is a programmed divider which produces certain frequencies. These frequencies are a factor of the oscillator frequency. The beat generator is also a programmed divider which contains 15 available beats. Four beats of these can be selected.
There is an inbuilt oscillator circuit that serves as a time base for beat and tone generator. It has a 62 notes ROM to play music. A set of 4 bits controls the scale code while 2 bits control the rhythm code. When power is turned on, the melody generator is reset and melody begins from the first note. The speaker can be driven by an external npn transistor connected to the output of UM66.
Many versions of UM66T are available which generate tone of different songs. For example, UM66T01 generates tone for songs ‘Jingle bells’, ‘Santa Claus is coming to town’ and ‘We wish you a merry X’mas’.
BC548
BC548 transistor
The BC548 is a general purpose epitaxial silicon NPN bipolar junction transistor found commonly in European electronic equipment. The part number is assigned by Pro Electron, which allows many manufacturers to offer electrically and physically interchangeable parts under one identification. The BC548 is commonly available in European Union countries. It is often the first type of bipolar transistor young hobbyists encounter, and is often featured in circuit diagrams and designs published in hobby electronics magazines.
If the plastic TO-92 package is held in front of one's face with the flat side facing toward you and the leads downward, (see picture) the order of the leads, from left to right is collector, base, emitter.
BC548 is general purpose silicon, NPN, bipolar junction transistor. It is used for amplification and switching purposes. The current gain may vary between 110 and 800. The maximum DC current gain is 800.
Its equivalent transistors are 2N3904 and 2SC1815. These equivalent transistors however have different lead assignments. The variants of BC548 are 548A, 548B and 548C which vary in range of current gain and other characteristics.
BC 558
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BC558 is a general purpose PNP transistor. It is used in switching and amplifier applications. The DC current gain varies in range 110 to 800. It is also used as a complement for transistors BC546 to BC550.
The transistor terminals require a fixed DC voltage to operate in the desired region of its characteristic curves. This is known as the biasing. For amplification applications, the transistor is biased such that it is partly on for all input conditions. The input signal at base is amplified and taken at the emitter. BC558 is used in common emitter configuration for amplifiers. The voltage divider is the commonly used biasing mode. For switching applications, transistor is biased so that it remains fully on if there is a signal at its base. In the absence of base signal, it gets completely off.