EX-IOExpander FAQ and Troubleshooting

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Frequently Asked Questions

This is a list of common questions that we answer by our various support channels:



What microcontrollers can be used with EX‑IOExpander?

At present, Arduino Nano, Uno, and Mega2560 (see Supported Devices)

Troubleshooting tips

In this section, you will find some tips on troubleshooting the various issues encountered with EX‑IOExpander.

EX-IOExpander device offline


Common Causes

I/O activities are not working
Diagnostic command <D HAL SHOW> reports device as offline
I2C connectivity issue between EX‑CommandStation and EX‑IOExpander - ensure SDA connects to SDA, SCL to SCL, and ground is connected
EX‑CommandStation turned on before EX‑IOExpander - ensure EX‑IOExpander is turned on before EX‑CommandStation
Incorrect I2C address defined - ensure the I2C address is correct in myHal.cpp on EX‑CommandStation and myConfig.h on EX‑IOExpander
Incorrect number of digital/analogue pins defined - ensure the pins defined in myHal.cpp are valid according to Supported Devices
I2C clock speed issue, define slower clock speed in myHal.cpp: Changing the Clock speed

Digital pin 13 is always low in input mode

On non-genuine Uno devices (possibly Nano also), the onboard LED can cause this behaviour when pullups are enabled, with a suggested workaround of adding an external 1K pullup resistor