Lab Person Counter

A simple ESP8266 and MAX7219 based contraption to easily let people count themselves when entering the Makerspace. Tested with nodemcu and wemos d1 mini chips.

Wiring

Increase Button

D4 and GND

Decrease Button

D3 and GND

MAX7219 panels (at least 4)

CLK_PIN   D5
DATA_PIN  D7
CS_PIN    D8
VCC       5V
GND       GND

Full Status Output (driven high when full capacity is reached)

D0

Vacant Status Output (driven high when not at full capacity)

D1

Both output pins can also be changed by redefining VACANCY_FULL_PIN and VACANCY_VACANT_PIN

#define VACANCY_FULL_PIN        D0
#define VACANCY_VACANT_PIN      D1

Analog PWM Control Input

A0

Can also be changed by redefining VACANCY_PWM_CONTROL_PIN

#define VACANCY_PWM_CONTROL_PIN A0

Vacancy Status Output

Inverted Output

The vacancy status output pins can also be configured to be inverted, or drive a PWM signal that may be controlled via the analog input A0.
To invert the output signals (so that they are driven low on activation), modify the following definition to 1. This does not affect PWM output.

#define VACANCY_INVERT_OUTPUT   1

PWM Output

To output a PWM signal, set the following definition to 1, and optionally change the frequency with the VACANCY_PWM_FREQUENCY definition.

#define VACANCY_PWM_ENABLED     1
#define VACANCY_PWM_FREQUENCY   1000

The duty cycle of the PWM signal can be optionally controlled via an analog input from the A0 pin.
The multiplier applied to the read value can be changed by modifying the VACANCY_PWM_MULTIPLIER definition.

#define VACANCY_PWM_MULTIPLIER  0.15

Slack notifications / Reporting

To make use of Slack notifications whenever the number of people changes, create an incoming webhook for your slack workspace.
You will get a unique URL looking something like this: https://hooks.slack.com/services/...
Fill the webhook variable with this URL and the lab person counter will automatically announce any change to the channel that is set up for your webhook.

const char* webhook = "https://hooks.slack.com/services/..."

Debouncing

The notifications can be "debounced". This means that a notification will only be sent after a defined amount of time t after the last status change.
This prevents spamming of notifications on quick successive status change, for example when a lot of people arrive or leave at once.
This debounce time t can be changed via the UPDATE_DEBOUNCE_MS definition, and must be specified in milliseconds.

#define UPDATE_DEBOUNCE_MS      (30 * 1000)

Usage

Before flashing set the ssid and password. Until the Display gets polled it shows it's IP. It expects a request in under 10s or it goes back to showing it's IP.

A Request to http://<IP>:80/ will receive a Response with content type application/json. It's content might look like this:

{ "number": 0 }