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Alex

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  1. Hi all, I have some questions about the 8 Line Intercommunication using 89c51 project. (Link: http://www.electronics-lab.com/projects/telephone/017/) First of all: where are the source files for the 89c51? ;) Next, I think I've spotted some errors in the schematics: The MT8816 is powered from the wrong supply lines! According to the datasheet the maximum supply voltage (Vdd-Vee) is 13.2 V. So, the Vdd should be lowered at 5 V, or the Vee should be tied to GND (biasing the analog inputs at Vdd/2). On the SLIC cards, assuming the phones are connected between TELx and GND, R9 (100 Ohms, on SLIC 1 page, upper left) is connected in parallel to the phone, which is clearly wrong. May be should be 100K? Or it is connected in the wrong place? In the same area, the relay contacts are miswired: with the current layout, when the phone is ringing, the off-hook detector is disconnected from the phone! The + inputs of the comparators should have a resistor towards GND to set the on-hook/off-hook threshold (now, when on-hook, both inputs are at the same voltage, so the output is undefined). Thanks in advance, Alex
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