Hello, I'm currently working with a private protocol which uses only 2 wires and I have to replicate. The master device alternates the polarity of a 24v potential between the wires so it is sometimes +24v and others -24v (measured from one of the cables). The slaves answer by connecting and disconnecting an internal resistor to this potential and thus generating a current. In order to replicate the +24v/-24v master part I'm using a transistor based H-bridge circuit, and to detect the slave answer I made a circuit in which the current passes trough a PNP transistor base to emitter, this generates a 24V potential in the collector and then I get the needed 3.3V logical 1 via a voltage divider. I simulated this circuit in falstads circuitjs (http://tinyurl.com/y7rf8v62) and it works like a charm, but when I made the circuit in the protoboard the collector of the PNP transistor is always at 24V, I used smaller values for the resistor divider and the collector voltage dropped but I cannot fully understand whats going on. Later connecting and disconnecting parts of the circuit I noted that this voltage in the collector only occurs when the 1K resistor is connected to the base but its other end disconnected as if there was an small current flowing though the air(?) Does somebody understand what's going on, what causes this small current and collector voltage?
TLDR: I detect 24V in the collector of a PNP transistor when the emitter is connected to 24V and the base is connected to a 1K resistor whose other end is disconnected.
TLDR: I detect 24V in the collector of a PNP transistor when the emitter is connected to 24V and the base is connected to a 1K resistor whose other end is disconnected.
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