On-Hook Anti Toll Fraud Device Circuit Diagram

Published:2011/8/9 18:26:00 Author:Vicky | Keyword: On-Hook, Anti Toll Fraud | From:SeekIC

On-Hook Anti-Toll-Fraud Device The circuit controls the on-off of relay by making use of the changes of voltage brought by on-hook and off-hook of the telephone. S is a exterior switch, which is closed usually. Usually the high voltage of the external line can guarantee the regular work of V (the current of collector is 4mA). The relay works, and the closed contact of K is open, which does not affect the usage of the telephone. When there is toll fraud in the external line, the voltage of the line is lower than 8V, K does not work, and the closed contact makes the external telephone T and R under short circuit. Therefore the external telephone T and R cannot work then. The user can open S, and close it after VD3 is lighted. Then the circuit is under anti-toll-fraud situation.



Reprinted Url Of This Article:
http://www.seekic.com/circuit_diagram/Electrical_Equipment_Circuit/Telephone-Related_Circuit/On_Hook_Anti_Toll_Fraud_Device_Circuit_Diagram.html

Print this Page | Comments | Reading(3)