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New Member

I'm trying to make a communication circuit with PIC and HT9200 / 9170.

I need to send power and data in a pair of wires as used in phones.

I'm having problems in the modulation and demodulation of the signal, I do not know the correct way to send power and data.

If anyone has any knowledge or can help me in the right way to send the data I will be very grateful.


Tony Stewart

Well-Known Member
Most Helpful Member
Data is Z_cap coupled to input.
Power is Z_choke coupled to input. Choose Z so chokes with 100x shunt units does not load data line. This makes L too big.

Or consider PoE like interface with bi-phase data instead of DTMF to raise carrier f and Z_choke ...e.g. 100kHz or 1MHz. with differential bi-phase and terminations at both ends to match cable Zo with high Z ports using CML.
Last edited:


Well-Known Member
Most Helpful Member
In telephone systems, the device or circuit that interfaces two unidirectional audio signals (one incoming and one outgoing) onto a bidirectional wiring system is called a hybrid. Search for things like telephone schematic and hybrid circuit schematic to see how it is done. Note that what you want to do will be much more difficult because of the total system power level.

While what you are asking about has been around for 130 years, that doesn't make it a beginner's project. What is your skill set for analog circuit design or assembly, what kinds of components do you have access to, where are you located, etc?

Also, how much power is needed at each location? At only 1 W per slave, you are going to have to modulate the tones on top of 100 W of DC power. Sure it can be done, but each slave will need a large heatsink.

Are you sure you are limited to only 2 wires? Three would make a huge difference in the overall complexity and cost of the system.

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