Caller ID Display

Posted on Oct 22, 2012

CallID Unit based on Motorola MC68HC11A1P & MC145447P chips compatible with the standard protocols. if you got a multimeter and a phone you can start testing. Check the voltage across the pair, should be 48VDC in US, 60VDC in Europe. Place a 600 ohm resistor, 5W across the pair and measure the current should be 20 to 40mA (holding current) While on-hook the Ring will have a negative voltage and the Tip will be grounded through equipment at the Central Office UNLESS the office is a `Floating Battery` type office. In the latter case the Ring will have a negative voltage and the Tip will have a positive voltage. The sum of the two voltages (which are in series) will be about 48 to 52 Volts. The usual way of doing this is to use a bicolor LED that glows read with one polarity and green when the polarity is reversed.

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