What is the maximum voltage for the optical input on the Alpha GSM Alarm Dialer?

Hello.  What is the maximum voltage for the optical input and what is the voltage required to power the board? Thanks


Advent Controls Alpha GSM Auto Dialer Input Circuit Diagram

Input Circuit Diagram

The input features a 13v overload protection diode and can handle DC voltages up to about 30v.  The input impedance is 4400ohms relative to the +VE supply as can be seen in the input circuit diagram above.  The +V terminal is normally at +VE minus approximately 1.3v which is dropped over the opto-isolator LED.  When the +V terminal is connected to ground current flows from +VE through the resistors R17&R18 and the opto-isolator LED to ground.  This activates the transistor on the digital section shown above.

The input is active low… active when pulled to ground. You can invert the voltage level which causes triggering of the calls/text but your application needs to be able to pull the input to ground when either active or when idle. It can go to any voltage up to about 30v in the other state.  If you have an output which goes positive you can use a low value resistor (~300-600ohms) to pull the input low in the off state.

Most burglar alarms connect the bell -ve supply to ground when the alarm is sounded making this connection ideal.

The board will operate from about 9 to 24VDC.




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