I have a buzzer hooked up to pin A7 (WKP) and a high-frequency low volume tone comes from it only when the device is plugged in and charging on the Eseries. Even with the notone function called and also analogwrite(pin,0).
I have the same buzzer and firmware hooked up to a P1 and this noise doesn’t come from the Buzzer.
I’ve tried many different things, but what I’ve concluded is that this ONLY happens when the charging circuit on the E-series is active. As soon as I unplug external power the high-frequency noise stops immediately.
I am thinking that there is either EMI from the charger, causing the buzzer to energize or the WKP pin is doing something weird when the charger is active.
Any thoughts on this would be appreciated.