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DTMF Tone Alarm Dialer Circuit

2016-02-19 10:42  
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Automatic Dialers are a NEW GENERATION of Security Communications and Notification equipment for the Security Professional. Small, Compact and User Friendly. USP Dialers deliver the most advanced technology in the World today. Available in Models ranging from single to 4 alarm zones. USP Dialers deliver voice messages in any language and will call up to 8 telephone or cell phone numbers.This circuit dials a stored DTMF tone sequence from EPROM when a control line is taken to 0 V. ICl is a Schmitt trigger oscillator, running at around 2 Hz. It clocks a 4024 binary counter. The counter`s outputs connect to the address leads of the EPROM. A 2716 was used here, but the choice of EPROM is by no means critical. Normally, the counter is held reset by a logic 1 on its reset pin (pin 2). When the trigger input is sent low, pin 10 of ICl goes low, pin 3 goes high, and the reset is removed from the counter. It then begins to clock, incrementing the EPROM.A wireless alarm dialer is programmed to contact any saved telephone numbers, via a cellular signal, in the event that the home security system is triggered.

Alarm Dialer Circuit 

When moved from address 000000, the data on bit DO of the EPROM changes to a logic 1 and holds the circuit running. The last address should have data 11111110 to reset the circuit to standby.