arduino_gauge_controller/wiring.md

Wiring

This document describes the wiring required for the current integrated system:

• Arduino Mega 2560
• HV5812P VFD driver
• 4-digit VFD tube with decimal point and alarm bell
• 3 stepper-driven gauges
• WS2812B LEDs
• ESP32 running gauge.py as the MQTT / Home Assistant bridge

It is intentionally based on the code that is in the repository now:

• Gaugecontroller.ino
• gauge.py

System Power

You effectively have three power domains:

1. 5V logic for the Arduino Mega logic, the HV5812 logic side, and usually the step/dir logic inputs
2. high voltage for the VFD for HV5812P VPP and the VFD segment/grid drive
3. motor / actuator power for the stepper gauges and their driver hardware

Minimum common rule:

• all logic grounds must be common

That means these must share GND:

• Arduino Mega GND
• ESP32 GND
• HV5812P logic GND
• stepper driver logic GND
• WS2812B GND

The VFD high-voltage supply still references the same ground, but its high-voltage nodes must never be connected directly to Arduino or ESP32 GPIO pins.

Arduino Mega 2560

Use the Mega as the central logic controller.

Power:

• Mega 5V <- regulated 5V logic supply
• Mega GND <- common logic ground

Serial bridge to ESP32:

• Mega RX1 pin 19 <- ESP32 TX GPIO 17
• Mega TX1 pin 18 -> voltage divider -> ESP32 RX GPIO 16
• Mega GND <-> ESP32 GND

This matches the current code:

• Arduino uses Serial1 in Gaugecontroller.ino
• ESP32 uses UART(1, tx=17, rx=16) in gauge.py

Because the Mega transmits 5V logic and the ESP32 expects 3.3V logic on RX, add a resistor divider on the Mega TX1 -> ESP32 RX line.

Suggested simple divider:

• Mega TX1 -> 1 kOhm resistor -> divider node
• divider node -> 2 kOhm resistor -> GND
• divider node -> ESP32 GPIO16 (RX)

That scales the Mega's 5V TX signal to roughly 3.3V for the ESP32 RX input.

VFD Control: Mega -> HV5812P

These are the integrated pin assignments used by the merged controller:

Mega Pin	HV5812P Signal	Purpose
D46	DATA IN / DIN	serial data into HV5812P
D47	CLOCK / CLK	shift clock
D48	STROBE / LATCH	latch transfer
D49	BLANKING / OE	output blanking
5V	VDD	HV5812 logic supply
GND	GND	common reference
VFD HV+	VPP	HV5812 high-voltage rail

Important:

• VDD is the low-voltage logic rail
• VPP is the high-voltage output rail
• do not connect Arduino 5V to VPP

HV5812P -> VFD Tube

The current output map is:

HV5812 Output	Tube Function
HVOut1	segment A
HVOut2	segment B
HVOut3	segment C
HVOut4	segment D
HVOut5	segment E
HVOut6	segment F
HVOut7	segment G
HVOut8	decimal point segment
HVOut9	alarm bell segment
HVOut10	digit grid 1
HVOut11	digit grid 2
HVOut12	digit grid 3
HVOut13	digit grid 4
HVOut14	indicator grid between digits 2 and 3

Logical segment layout:

 ---A---
|       |
F       B
|---G---|
E       C
|       |
 ---D---

Additional VFD wiring notes:

• the VFD filament/heater wiring is separate from the HV5812 outputs
• the exact filament supply depends on your tube
• the HV5812 only drives the segments and grids

Gauge Control Pins

The current sketch drives three gauges.

Each gauge needs a driver or actuator input that accepts:

• DIR
• STEP
• optionally ENABLE if you later add one in code

Current assignments:

Gauge	Mega DIR	Mega STEP
Gauge 0	D50	D51
Gauge 1	D8	D9
Gauge 2	D52	D53

Connect each pair to the matching stepper driver inputs.

Example:

• Mega D50 -> Gauge 0 driver DIR
• Mega D51 -> Gauge 0 driver STEP
• Mega D8 -> Gauge 1 driver DIR
• Mega D9 -> Gauge 1 driver STEP
• Mega D52 -> Gauge 2 driver DIR
• Mega D53 -> Gauge 2 driver STEP

Also connect:

• Mega GND -> each driver logic ground

If your driver boards need separate motor power, supply that from the proper motor supply. Do not power motors from the Mega 5V pin.

WS2812 LED Strips

The current sketch expects two LED data chains. Backlight and status LEDs stay on the main strip; the red/green dial indicator LEDs are on their own strip.

Mega Pin	LED Strip
D22	main backlight/status DIN
D36	indicator DIN
5V	both strips 5V
GND	both strips GND

Notes:

• the command protocol still exposes 7 LEDs per gauge
• logical indices 0-2 are backlight, 3-4 are indicators, and 5-6 are status
• use a proper 5V supply sized for the LED current
• keep LED ground common with the Mega

If the strip is powered from a separate 5V supply:

• connect external 5V -> LED 5V
• connect external GND -> LED GND
• connect that same GND to Mega GND

ESP32 Bridge

The ESP32 runs gauge.py and talks to the Mega over UART and to Home Assistant over MQTT/Wi-Fi.

ESP32 to Mega:

ESP32 Pin	Mega Pin	Purpose
GPIO17	RX1 pin 19	ESP32 TX -> Mega RX
GPIO16	TX1 pin 18	ESP32 RX <- Mega TX
GND	GND	common ground

ESP32 power:

• power the ESP32 from a proper 3.3V or board-supported USB/5V input, depending on your board
• do not feed raw 5V into a bare 3.3V ESP32 module unless the board has its own regulator

One-Page Wiring Summary

Power

• 5V logic supply -> Mega 5V
• 5V logic supply -> HV5812 VDD
• 5V logic supply -> WS2812B 5V
• motor supply -> gauge driver motor power inputs
• VFD high-voltage supply -> HV5812 VPP
• all grounds common

Mega to ESP32

• Mega 19 (RX1) <- ESP32 GPIO17 (TX)
• Mega 18 (TX1) -> resistor divider -> ESP32 GPIO16 (RX)
• Mega GND <-> ESP32 GND

Resistor divider on Mega TX1:

• Mega TX1 -> 1 kOhm -> divider node
• divider node -> ESP32 GPIO16
• divider node -> 2 kOhm -> GND

Mega to HV5812

• D46 -> DIN
• D47 -> CLK
• D48 -> STROBE
• D49 -> BLANKING
• 5V -> VDD
• GND -> GND
• VFD HV+ -> VPP

HV5812 to Tube

• HVOut1..7 -> segments A..G
• HVOut8 -> decimal point
• HVOut9 -> alarm bell
• HVOut10..13 -> digit grids 1..4
• HVOut14 -> indicator grid

Mega to Gauges

• D50/D51 -> gauge 0 DIR/STEP
• D8/D9 -> gauge 1 DIR/STEP
• D52/D53 -> gauge 2 DIR/STEP

Mega to LEDs

• D22 -> WS2812B DIN
• 5V -> WS2812B 5V
• GND -> WS2812B GND

Sanity Checklist Before Power-On

• Mega, ESP32, HV5812 logic, LED strip, and driver logic grounds are all common
• Mega D46-D49 go to the HV5812, not to the gauge drivers
• Mega D50-D53 and D8-D9 go only to the gauge drivers
• HV5812 VDD is 5V
• HV5812 VPP is the VFD high-voltage rail, not 5V
• ESP32 UART is crossed correctly: TX -> RX, RX -> TX
• WS2812B has its own adequate 5V supply if current draw is significant
• motor power is not coming from the Mega

What This Does Not Define

This document does not define:

• the exact VFD filament supply voltage/current
• the exact motor driver board power pins, because that depends on the driver hardware you are using
• the physical PDIP package pin numbers of the HV5812P