@ruslancc Unknown but I have fixed that now. It could be that the M5Stick can not provide enough power for the heart rate monitor. You could try connecting one of these https://m5stack.com/collections/m5-accessory/products/grove-t-connector-5pcs-a-pack [image: GROVE-T_1200x1200.jpg?v=1566377200] between the Stick and the heart rate monitor and use the other connection to provide an additional power supply for the monitor.