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Post: Hi Rhys A 10K resistor between ground and the IO Pi input should just increase the current draw from your sensor by 0.5mA. The idea behind using a pull-down resistor is when the voltage from the sensor drops to 0V any voltage on the input wire left over from capacitance in the wire and IO input will flow through the resistor to ground pulling the voltage down to 0V. It would not limit the current going to the input pin, which is done internally in the IO chip and when the pin is set as an input it should only draw around 1µA, well below the 125mA the chip is designed to handle. The most common cause for the IO chip getting hot is too much current being drawn from the pins when they are set as outputs. Each output channel can source up to 20mA but it normally takes more than that for the chip to warm up. As you have set the IO bus as inputs it shouldn't be drawing anywhere near enough power to get warm. Another possibility is the voltage on the input is too high. The maximum voltage for the input is 5.5V so if the voltage on an input is above that it could make the chip get hot and stop working correctly. When you measured the voltage on the sensor did you measure between the output and the ground on the sensor or the ground on the Raspberry Pi? A ground loop problem where the grounds are not all connected together properly could cause a potential difference between different parts of the circuit so while the voltage between the sensor output and the sensor ground would be 5V the voltage between the sensor output and the Raspberry Pi ground could be a different value. I had an issue once where I used two switch-mode power supplies and did not connect the grounds together correctly. The result was accidentally pushing 125V into the GPIO header on a Raspberry Pi which luckily only killed the UART pins. The third possibility is a fault with the chip on the IO Pi Plus. As a faulty board could explain the problems you are having I will send you a replacement tomorrow so we can rule that out as the issue. Do you want me to send it to the same address as your previous order? When the new board arrives it may be worth adding an extra 10K resistor on each input as shown in the diagram below. This will limit the current that can flow into or out of the IO Pi reducing the risk of damaging the board. Also before you connect your sensor to the IO Pi try testing it first by connecting the inputs to the 5V pin on the Raspberry Pi GPIO header via a 10K resistor. That will allow you to make sure the IO Pi is working correctly and narrow the problem down to the sensor output. [img]/docs/forumpost/0ctu4ma.png[/img]