How to safely use TRRS socket in order to transfer signal

Question

In order to build a split keyboard I want to connect the two pieces with a four wire cable. Among the keyboard enthusiasts forums I have seen often the use of a trrs cable which is used as V,Gnd,TX,RX or V,Gnd,SDA,SCL depending on the communication protocol.

Yet, many people have mentioned the problem of short-circuit when the male pin enters or leaves the female socket, because the tip of the pin may contact to the tip, rings or the sleeve of the socket.

Is there a safe way to arrange the voltage, ground and signal pins of the socket in order to avoid any damage due to accidental contact?

Answer 1

^{simulate this circuit – Schematic created using CircuitLab}

Figure 1. A traditional connection.

Assuming the socket is on the powered device (rather than on the keyboard) the traditional approach seems best to me.

• You need to be confident that you can short TX to +5V without damage. If that's OK then, as shown in Figure 1, nothing bad can happen until the tip reaches the +5V tip.
• As it does so it may short TX to +5V.
• It may also apply the +5V to the keyboard before the ground connects. If this happens the whole keyboard will be at +5V and so +5V may come back on the RX.
• Possibly the worst case is +5V connected, GND not connected and TX driven low. You'll need to check if the circuitry can tolerate that.