PiXtend V2 -L- Hardware Manual
Connection Notes
The following diagram illustrates the connection of small consumers to the PiXtend GPIOs
(as outputs).
Standard light-emitting diodes can be connected directly to the GPIOs. However, it is first
necessary to calculate whether the current is suitable for the respective LED.
Example Calculation:
green standard LED: forward voltage 2.1 V
(Output voltage - forward voltage) / internal series resistor = current
(5 V - 2,1 V) / 300 Ω = 9,67 mA
Standard LEDs usually light up from approx. 2 mA and tolerate at least 20 mA. It is
therefore possible to connect a green LED directly between a GPIO output and GND.
If the outputs are to be connected to TTL inputs of other devices, make sure that the input
resistance is not less than 1 kΩ. Otherwise, the voltage at HIGH level may not be sufficient
to be recognized by the input of the other device (voltage divider between internal 300 Ω -
PiXtend internal and the resistance of the remote).
The GND connections shown externally in Figure 68 must be connected to the PiXend
GND at at least one point in order to close the circuit.
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Figure 68: Principle circuit diagram: Connection of the PiXtend V2 -L- GPIOs (as outputs)
