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Espruino is a JavaScript interpreter for low-power Microcontrollers. This site is both a support community for Espruino and a place to share what you are working on.
@gmurphy
I felt guilting for asking, so I naively tested what I could, and found the following current draw (tested on an Espruino MDBT42Q Breakout, post flash+reset, with setWatch on 5 pins):
Service+Characteristic:
Idle: ~0.2mA
Connected: ~0.43mA
Keyboard HID:
Idle: ~0.2mA
Connected: ~0.43mA
My ammeter isn't good enough to know how much power is used for sending key presses or service update notifications, but I assume it's similar. Based on the numbers being the same, using a GATT Characteristic seems much better for my case because I can control the connection programmatically on the PC side, and differentiate between senders more easily, but would love insight from others if you know better (I'm still curious about send the characteristic changes without the active connection, because I don't care about exclusivity)