No. The USB signals aren’t standard serial. You would need a USB master device at the other end.
The Serial1 RX and TX lines (Arduino pins 0 and 1) are unused and are brought out to pads on the back of the Arduboy’s circuit board. You could connect them to a ESP8266 and control them using the Arduino Serial interface.
Note that the standard ESP8266 is a 3.3V device so you may need a regulator for power and level shifters for the signals, to interface one to the Arduboy.
You could also connect these RX and TX lines to another Arduino (or any other device that can accept standard async serial signals). Again, you may need level shifters.
No. D15, D16, and D17 are the SPI signals and are connected to the display.
A4 and A5 are under the battery, above RESET, GND and VCC. AREF is not an I/O pin. It’s used to provide a reference voltage for the ADC used by the analog inputs.
[quote=“Ruben_Speybrouck, post:6, topic:1568”]On which arduino board is the arduboy based?
It uses the Arduino Leonardo bootloader and so can be considered to be a Leonardo.
The Arduboy uses the raw battery voltage as VCC. It’s normally around 3.6V but can go up to 4.2V when fully charged (and down to about 3.1V when discharged). The ESP8266 is specified maximum 3.6V so you risk damaging by it running directly from the Arduboy’s Vcc.
You could use a low dropout 3.3V regulator, fed from the Arduboy’s Vcc, to power the ESP8266 but the Arduboy could still output up to 4.2V on its signals, so you would need some kind of level shifters on the output(s) of the Arduboy that are feeding input(s) on the ESP8266.
The WeMos D1 mini has an on board 3.3V regulator, which can be used to power its ESP8266 module, but you would still need to convert the TX/D1 signal from the Arduboy to a maximum of 3.3V to feed it to the RX pin of the WeMos D1.
For level conversion you could use one of these, which are available on eBay from various vendors.
After looking at the WeMos D1 schematic, I’m not sure it would be a good choice to use with the Arduboy.
It has an on board USB to serial converter which would only be used to program the ESP8266. At other times it would needlessly draw power and shorten the battery life.
The serial converter is connected to the TX and RX lines of the ESP8266 which may interfere with the TX and RX signals from the Arduboy.
The USB connector provides 5V to the on board 3.3V regulator. If the 5V pin were connected to the Arduboy’s battery and the USB was connected, 5V would be fed to the battery which could cause it to overheat and explode!