Nixie Counter

Description / Overview

PCB for a physical "people now present" counter that sends it data directly to the SpaceAPI.

Microcontroller

The microcontroller is a STM32F103 based "Blue Pill" board. We chose this because it's very cheap, very widely available and it can run firmware written in Rust.

WiFi

Data is sent via WiFi using an ESP-01 module. The module is controlled by the Blue Pill through AT commands over a serial connection.

Input Methods

To enter the number of people present, a 2-position momentary toggle switch is used that can be pushed upwards or downwards.

Display

The number of people present is then displayed on two IN-12B nixie tubes. Those tubes need 150-160 V for turning on, for this we use a NCH6100HV module. The tubes are controlled through two K155ID1 BCD-to-Decimal drivers. Those need 5V logic levels, so we use a level shifter between the drivers and the microcontroller.

Power Supply

Input power is supplied at 12V. The nixie power supply converts that to ~150V.

Two LDOs convert the 12V to 5V (for the nixie drivers) and 3.3V (for the rest).

Status LEDs

There's a yellow LED to indicate that the controller has power and runs the correct firmware, and a green LED to indicate whether the ESP-01 module is connected to the WiFi or not.

PCB

Editing

This is a LibrePCB project!

License

TAPR Open Hardware License, see LICENSE.txt.