ESP32

The ESP32 devboard we’re using has most pins of the ESP32 exposed, so we have a lot of GPIO’s available (which we will need!).

The table below gives all the inputs we need

ESP32	VFD	Key pins	Slider pins	Description
5V	-	-	-	5V input from 5V regulator
?	-	-	-	Test LED (blinking)
-	1	-	-	Filament F-
3.3V	5	-	-	Vdd, same for ESP32 Vdd
-	8	-	-	Vdisp-ON, to enable Vdisp, via the NPN-PNP high side, dual power rail transistor circuit
?	-	-	-	Vdisp_ON signal from ESP32, via transistors
GND	7	-	-	GND common ground (V-)
-	8	-	-	OSC circuit for VFD
?	9	-	-	RST reset pin VFD
GP5	10	-	-	CS Chip Select SPI
GP18	11	-	-	CLK Clock for SPI (VSPI)
GP23	12	-	-	DIN Data input for SPI (VSPI MOSI pin on ESP32)
GP19	-	-	-	VSPI MISO pin on ESP32, not usable as it is read by the SPI library
-	45	-	-	Filament F+
TX0	-	-	-	Serial port
RX0	-	-	-	Serial port
GP25	-	-	-	Audio DAC
GP12	-	-	-	SPI output from 74HC165 shift registers (HSPI MISO pin on ESP32)
GP13	-	-	-	HSPI MOSI pin on ESP32, not usable as it is used by the SPI library
GP14	-	-	-	SCK Clock for SPI (HSPI)
GP15	-	-	-	LOAD trigger for SPI
GP2	-	8	-	Key scan output
GP4	-	9	-	Key scan output
GP16	-	10	-	Key scan output
GP17	-	11	-	Key scan output
GP27	-	-	5	Slider scan output
GP26	-	-	6	Slider scan output
GP33	-	-	7	Slider scan output

For the 12 input pins, we will use two daisy-chained 74HC165 as described here => paralel to serial. These chips have internal pull-down resistors, so we don’t have to worry about that.