Hi friends,
one more circuit: DTMF decoder interface for designing Caller ID Unit. It's very simple circuit using DTMF decoder MT8870 (or CM8870). As shown in the circuit, u'll receive an interrupt ( if NAND output is connected to INT of the microcontroller) whenever u receive a call or make a call and then u can use yr program to read the digits coming out of pin 11 to 14 of the MT8870. I designed the circuit with additional features like seperating received calls, missed calls, dialled numbers along with telephone directory.
Download datasheet:
To determine whether number is dialled or received, u need to know whether receiver is on-hook or off-hook. following simple circuit will give u that indication:
I had used microcontroller 8951 with16x2 LCD and Dallas nvRAM for storing numbers and names. The code is in assembly language. It's really easy to make this one with lot of variations.
Ring Detector for Caller ID Unit
Hi Friends,this is an addition to the caller ID circuit of my previous post. For deciding whether call is received call or missed call, u need to monitor the ringing signal along with the off-hook detector signal, which is discussed in the last post. If the off-hook detector signal goes low (i.e. receiver lifted) before the ringing signal stops, then the call is labeled as received call, otherwise it is a missed call.
This small circuit converts the ringing signal (sine wave 90vrms) into 5v dc pulses which can be directly fed to microcontroller pin. The circuit outputs a pulse for each ring. The delay between two pulses is to be monitered and if it exceeds 4 sec, then ring is dead, hence, the call is missed call.!
Try it out.. This small circuit converts the ringing signal (sine wave 90vrms) into 5v dc pulses which can be directly fed to microcontroller pin. The circuit outputs a pulse for each ring. The delay between two pulses is to be monitered and if it exceeds 4 sec, then ring is dead, hence, the call is missed call.!
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