Author Topic: Searching for bus!  (Read 2057 times)

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Offline PCB.Wiz

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Re: Searching for bus!
« Reply #25 on: April 14, 2019, 11:52:46 pm »
The nodes need usually 3-5mA @ 3.3V at most of the case, and in some states where action happens, the current will go up to 100mA @3.3V.

For how long does it need 100mA ? Is that a responding node, or is there a chance all nodes can demand 100mA at the same time ?
Can you ensure no slave is demanding 100mA during a narrow reply-window ?

I had my own theory of implementing a bus, but surely, a already available solution would overcome my idea in any ways, yet here is my idea.

Imagine a 24V Signal. Now to start a bus transmission, the node would raise the voltage to 25V giving 1V as a LOW signal. High bytes would put another 1V up, so you get 2V for a high signal. By raising the voltage to 25V, other devices would see "that the bus is already in use".
If you use linear regulators, (or even current diodes, common for LEDs these days) you can modulate any swing you like above dropout for one direction. (PSU -> Slave)
That leaves the other direction and that gets trickier.
If you know the current profiles of the slaves, the may be room to current modulate a reply that can be decoded to ignore normal operating current changes.
Otherwise, there are power-break-send-in-gaps  designs, those works best with lowest power nodes,  as the power needs a CAP reservoir during send.

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