Hello @RolfF It's a design mistake. It is a basic mistake to add 5V to 3.3V system. 5V enters the RF circuit, causing deterioration or damage. There are many cases where ATOM has already broken. : M5Stack Community Short Wifi effective range and IO0=3.9V issue with Lite and Matrix : About a year ago https://forum.m5stack.com/topic/3048/short-wifi-effective-range-and-io0-3-9v-issue-with-lite-and-matrix : M5Stack Community New CH552 firmware for Short-Wifi-Issue of M5Atom/Stick/TimerCAM/etc. : About 9 months ago https://forum.m5stack.com/topic/3768/new-ch552-firmware-for-short-wifi-issue-of-m5atom-stick-timercam-etc : Bugs and measures for M5Stack ATOM : 2021.10.10 https://macsbug.wordpress.com/2021/10/10/bugs-and-measures-for-m5stack-atom/ : How to not change FW. Other measures : Low the voltage of GPIO_0. The voltage on GPIO_0 decreases and the transmit power increases. digitalWite(GPIO_0,LOW);