MLX90640 Low Refresh Rate


I am using MLX90640 for a project to detect human presence and I followed a tutorial online to test it (Tutorial followed: High Resolution Thermal Camera with Raspberry Pi and MLX90640 — Maker Portal). However, in the “Visualizing the MLX90640 - Real-Time Thermal Camera” and “Real-Time Interpolation of MLX90640” sections, I was only able to get figure output by using 4Hz for the refresh rate rather than 8 or 16 Hz. I read the datasheet for the sensor and it talked about how “Capacitive loading on an I2C can degrade the communication”, so I am thinking about adding a 10uF capacitor to the sensor to helo improve the refresh rate.

Has anyone here had the same issue with a lower refresh rate? If so, how did you solve it? Is adding a 10uF capacitor a reasonable approach?

Any help would be appreciated. Thank you in advance!


I don’t have an MLX90640, but I just want to point out that adding a capacitor is the opposite of what you want to do. Bus capacitance is a problem, because the higher the capacitance of the bus the longer it takes to increase the voltage on the bus to change signals, and therefore the slower the signalling is. You want less capacitance, not more. I’m not sure you can really do much to decrease capaciatance, aside from reducing the length of the cabling, or possibly reducing the resistance of the pull-up resistor on the I2C bus.

Thank you for pointing that out. It is indeed tricky to reduce the capacitance. I will see what else I can do. Thanks again!