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Adrian A. Baumann 9912fe82cc Documented wiring and layout

2026-04-21 00:52:18 +02:00

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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:

System Power

You effectively have three power domains:

5V logic for the Arduino Mega logic, the HV5812 logic side, and usually the step/dir logic inputs
high voltage for the VFD for HV5812P VPP and the VFD segment/grid drive
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 -> 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

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.

WS2812B LED Strip

The current sketch expects one shared WS2812B chain.

Mega Pin	WS2812B
`D22`	`DIN`
`5V`	`5V`
`GND`	`GND`

Notes:

the code expects 7 LEDs per gauge, so 21 LEDs total
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) -> ESP32 GPIO16 (RX)
Mega GND <-> ESP32 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

If you want, the next useful step is a second document with a literal bench-build checklist:

wire 1 from Mega D46 to HV5812 pin ...
wire 2 from Mega D47 to HV5812 pin ...
wire 3 from ESP32 GPIO17 to Mega pin 19

That would be the most practical format for cleaning up the desk wiring.

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