Analog values with W5500 Ethernet Shield and Mega


I’m using an Arduino (italy) Mega with the Seeed W5500 Ethernet Shield for reading analog inputs from potentiometers.

The Card and shield are connecting OK -

Here’s the problem -

On Analog pins 4 and 5 (on the shield) im seeing increased values as compared to the Mega (without shield) or, with my older Arduino 5500 Ethernet 2 card -

All Unused analog pins have been set to LOW (6,7,14,15)

Eg: the approx mid point of the pot on A4 shows a raw value of about 620 (+/- 1) when using the Seeed shield, and shows about 500 (+/- 1 ) when using the Arduino Ethernet2, or without the seeed shield

As i can see that the analog pins are just “connect thru” on the shield, i dont know why im seeing an increase in value/voltage…

Im using the Ethernet2 library…

any suggestions?




If you use the non-I2C analog port, the reading is the same with/without w5500 shield.

the w5500 is connected the a4/a5 with scl and sda.

for mega, the sda/scl are 20/21.

So i think the w5500 shorts the a4/a5 with scl and sda, then the pull up resistor impacts the readings. thanks.

oard I2C / TWI pins

Uno, Ethernet A4 (SDA), A5 (SCL)

Mega2560 20 (SDA), 21 (SCL)

Leonardo 2 (SDA), 3 (SCL)

Due 20 (SDA), 21 (SCL), SDA1, SCL1

thanks bill

ill check it out

are you saying i should avoid using A5/A5 on the 5500 shield with the mega?


Hi FC,

Please use the a0~a3, thanks.