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Are there any real-life examples for connecting sensors or embedded systems using just two wires that are simultaneously used for both for the energy supply and digital data transmission?

I'm particularly interested in cases in which the sender has to store energy to remain operable (so unlike when using phantom power for microphones, which provide an analog signal anyway).

For instance, the following sketch shows a sender connected to a receiver using a potentially long two-wire connection that is used for both supplying the sender with energy and for data transmission.

The data line is pulled up to 5 V by a pull-up resistor, and the sender can cause a logical 0 to the transmission line by temporarily closing the connection between the two lines. However, it can only send short bursts of data, as it must not deplete its capacitor before the transmission is over. The overall energy consumption of the sender is also quite limited in this way.

Connection between receiver and sender

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    \$\begingroup\$ Yes, it's somewhat confusingly called 1-wire: en.wikipedia.org/wiki/1-Wire We use it in some of our systems for internal temperature monitoring. \$\endgroup\$
    – vir
    Dec 29, 2020 at 17:18
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    \$\begingroup\$ Microwave LNA/mixer on a dish uses filters with phantom power too, as can BiPhase over DC \$\endgroup\$ Dec 29, 2020 at 17:24
  • \$\begingroup\$ AS-i (Actuator Sensor - interface) used in industrial systems sends data as (I think) a 1 V data signal superimposed on the 24 V nominal power supply. There is no need for riding out the dips in supply as there are none. \$\endgroup\$
    – Transistor
    Dec 29, 2020 at 17:27
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    \$\begingroup\$ RFID tags transmit information and power in the same signal and don't even use any wires. en.wikipedia.org/wiki/Radio-frequency_identification \$\endgroup\$
    – D Duck
    Dec 29, 2020 at 17:33
  • \$\begingroup\$ @Reudiger the naming is just aspirational, if there is already a common ground plane only one wire is required. \$\endgroup\$
    – crasic
    Dec 29, 2020 at 17:56

2 Answers 2

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Examples? There are 1-Wire, AS-Interface, and others, and this TI application note describes a way of doing it with several possible two-wire connections.

And yes, it is used often.

1-Wire pulls the line low for very short periods; the longest is the reset pulse (480 μs or more). 1-Wire slaves use the 1 state (which is also the idle state) to charge a small capacitor for operations while the bus is in the 0 state.

The capacitor is in the order of 800 pF, according to this design guide. There's a simplified schematic of a slave's internals on page 17 showing the parasitic power supply.

If there is enough idle time, you could charge a larger (external) power buffer for the slave, as long as you stay within specs.

AS-Interface works differently, and doesn't interrupt the power supply when sending data.

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  • \$\begingroup\$ Thanks for your answer! If I get it correctly, 1-Wire works similarly to the schematic. To quote Wikipedia, "Communication occurs when a master or slave briefly pulls the bus low, i.e., connects the pull-up resistor to ground through its output MOSFET. ". But please correct me if that is a misinterpretation. \$\endgroup\$
    – Ruediger
    Dec 29, 2020 at 18:41
  • \$\begingroup\$ See edited answer. \$\endgroup\$
    – ocrdu
    Dec 29, 2020 at 19:33
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Those plug-in internet providers for use in houses, between floors etc

Not going to name them, but can be a useful solution to provide internet access or improve poor wifi.

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