PCB for a physical "people now present" counter that sends it data directly to the SpaceAPI.
Microcontroller
The microcontroller is an ESP32C3 based M5Stack STAMP-C3U board. We chose this because it's quite cheap, has everything built-in that we need and it can run firmware written in Rust.
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.
An LDOs convert the 12V to 5V, for both the nixie drivers and the ESP32 module.
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 module is connected to the WiFi or not.
- When starting, the people count will be set to 0
- When pressing the toggle switch up or down, the people count will be modified and the nixie tube will show the sent number
- Every minute, the current count will be re-sent to the server (to allow server-side timeout implementations)
For the BOM, see
output/v2.0/assembly/Nixie_Counter_v2.0_BOM_Std.csv
and
output/v2.0/assembly/Nixie_Counter_v2.0_BOM_Std.html.
This is a LibrePCB project!
TAPR Open Hardware License, see LICENSE.txt.