Hey all, newbie here with a request for comments.
I work at a university that has a lot of emergency call boxes scattered around campus. These boxes have two buttons on them, one for emergency use and one for non-emergency use. The emergency button connects to the campus police 911 line, the non-emergency connects to the campus police department main dispatch line.
When these call boxes are first installed at a remote location, they are not programmed with the numbers needed to connect to those lines. I program them by dialing the remote location and then using the keypad to enter a set of numbers that set the emergency/non-emergency numbers, and some time delays for disconnecting a call.
The set of coded numbers is the same for all call boxes, so I've been thinking of ways to automate the process as much as possible. My current thought is along these lines:
create a microprocessor based DTMF tone generator that would generator the tones I've been entering through the keypad
couple that circuit between the phone base and handset via RJ9 couplers
to use, I'd pick up the handset and dial the remote callbox. After hearing that a connection has been established, I'd trigger the circuit which would send those tones over the wires that normally came from the handset microphone. After hearing a confirming set of beeps from the remote unit, I'd hang up and dial the next remote callbox.
I was wondering if anyone saw any problems with this idea and also if anyone knew what would be the appropriate voltage and current to use for the tone output. I'd use a DTMF generator chip for the signal waveform - would the output direct from the chip be likely to work?
Pic attached
I work at a university that has a lot of emergency call boxes scattered around campus. These boxes have two buttons on them, one for emergency use and one for non-emergency use. The emergency button connects to the campus police 911 line, the non-emergency connects to the campus police department main dispatch line.
When these call boxes are first installed at a remote location, they are not programmed with the numbers needed to connect to those lines. I program them by dialing the remote location and then using the keypad to enter a set of numbers that set the emergency/non-emergency numbers, and some time delays for disconnecting a call.
The set of coded numbers is the same for all call boxes, so I've been thinking of ways to automate the process as much as possible. My current thought is along these lines:
create a microprocessor based DTMF tone generator that would generator the tones I've been entering through the keypad
couple that circuit between the phone base and handset via RJ9 couplers
to use, I'd pick up the handset and dial the remote callbox. After hearing that a connection has been established, I'd trigger the circuit which would send those tones over the wires that normally came from the handset microphone. After hearing a confirming set of beeps from the remote unit, I'd hang up and dial the next remote callbox.
I was wondering if anyone saw any problems with this idea and also if anyone knew what would be the appropriate voltage and current to use for the tone output. I'd use a DTMF generator chip for the signal waveform - would the output direct from the chip be likely to work?
Pic attached
