I need to send and receive DTMF signals over a 24 Volt DC Line. Can anybody suggest how DTMF can be modulated over DC Line. I plan to decode it using MT8870 decoder. Any help/ guideline will be highly appreciated.
Put inductors at both ends of the line.
They should have roughly 1kΩ of imedance at the carrier frequency.
Now you can inject (via capacitors) any ac signal between these two inductors.
Thanks a lot for your advice. Can you please put up a small schematic ? Can you please guide what specific inductor value should be used for DTMF frequencies from 0-9 . I will be much grateful for your kind guidance
Put inductors at both ends of the line.
They should have roughly 1kΩ of imedance at the carrier frequency.
Now you can inject (via capacitors) any ac signal between these two inductors.
I don't think so. Most of DTMF receivers have op-amp at the input stage and it's gain can be adjusted with two external resistors, same as in an independent op-amp.