Bymakeriot2020

 FEB 17, 2022  ESP8266, IoT

A typical desktop oscillating fan

Desk or floor-standing fans are one of those appliances that will be present in almost every home or office. Some of the newer ones may already have remote control of some sort, while the older models won’t. It is however quite easy to do a retro-fitted controller to most of them, and at the same time, give them some (limited) intelligence.

Your typical oscillating fan does not have a lot of intelligence built-in. They normally consist of an electrical motor, with three separate windings, of varying inductance ( meaning the number of turns in the coil of wire will change the magnetic field generated, thereby changing the speed of the electric motor).

These windings have one common side, where all three of them are connected together, and the other three are separated. Normally the live wire from your mains supply (220v AC in my case) will go to this common connection. The neutral wire will go to the common of a four-position mechanical switch, with each winding going to one of positions 2,3 and 4 ( This results in a 3-speed configuration, with the first switch being off). It is also VERY important to note that this mechanical switch is hardware interlocked, meaning that ONLY one switch can be on at any given time… This is to ensure that electricity can only flow through one winding at a time. If you were to send electricity through multiple windings at the same time, the motor will still work, but not for very long…

A more modern Oscillating Fan

In order to automate an oscillating fan, we would thus need a way to switch the separate windings on and off, while preventing other windings from getting power at the same time. I chose to do this with SPST relays, as a proof of concept, and plan to design it with DPDT relays at a later stage to implement a proper hardware interlock, in addition to the software interlock implemented in the control software ( more on that later)

My requirements for the device are the following:

1) Must operate from mains power, using the existing power cord of the fan.

2) Must allow for local operation of the fan using the existing control buttons.

3) Must be able to update firmware OTA, and have WiFi connectivity for control via Home Assistant or MQTT

4) Must be capable of adding support for ESP Now protocol at a later stage

5) The fan must not have any visible modifications on the outside

The 3 speed Fan controller PCB

Taking all of my requirements into consideration, I have designed the following PCB to take care of my needs. As I do not require a lot of GPIO for this ( only 3 outputs, and 3 inputs ), I have decided to use an ESP8266-12E module from Espressif ( manufactured by AITinker, not sponsored by either company). This module is relatively cheap and has more than enough flash memory, RAM, as well as GPIO available.

Circuit Diagram – Page 1

Circuit Diagram – Page 2

As we can see, the circuit is minimal, with optical isolation on the relay drivers, a programming header, and a 3-way input for the mechanical switch.

The completed PCB, wired to the oscillating fan

As seen in the picture above, the wiring is quite simple, with the neutral wire looped to the common terminal of each relay (I had only green mains rated cable available, will replace it later with a proper white cable to keep to wiring standards). Black is live, with one wire going to the mains socket, and the other to the common of the motor coil windings. Light blue, yellow and white ( connected to the N/O terminal of the relays) corresponds to speeds 1, 2 and 3 of the fan.

At the top of the board, 3 wires go to the mechanical switch and a fourth to DC ground. (Note that there is no AC voltage on any of the switches. )

Mounting the PCB in the base of the oscillating fan

The PCB is mounted in the base of the fan while taking care to ensure that no AC cables are near the DC components. The ESP8266 chip is oriented to the side ( logo side of PCB ) to prevent interference to the WiFi signal. The mechanical switch is mounted into its original position, and its wires are routed away from any AC carrying wires to prevent interference.

It is important to note here that the firmware for the PCB was uploaded before assembly. You should NOT attempt serial uploading while the device is connected to mains power under any circumstances. ( While I have taken every precaution to ensure that AC and DC components of the circuit are separated from each other, it is just common sense to not try to upload firmware with mains connected)

The completed PCB shows the Upload port near the right top corner.

Uploading firmware:

Initial uploading of firmware can be performed by connecting a USB-to-serial adapter to the UPLOAD port and providing 5v and ground from the USB-to-serial adapter. The flash button is held down, and the board is reset, after which you can proceed with uploading, alternatively, you can also connect the DTR and RTS lines from the serial adapter to automatically reset the board and enter flash mode as needed. ( If your adapter supports this of course).

ESPHome configuration

The YAML configuration for ESPHome is listed below:

esphome:

name: esphome-web-18df94

esp8266:

board: nodemcuv2

# Enable logging

logger:

# Enable Home Assistant API

api:

ota:

wifi:

ssid: !secret wifi_ssid

password: !secret wifi_password

# Enable fallback hotspot (captive portal) in case wifi connection fails

ap:

ssid: "Esphome-Web-18Df94"

password: "verysecurepassword"

captive_portal:

sensor:

- platform: adc

pin: VCC

name: "ESP8266 Chip Voltage"

id: mcu_voltage

unit_of_measurement: "V"

device_class: "voltage"

accuracy_decimals: 2

update_interval: 60s

- platform: wifi_signal

name: "WiFi Signal Sensor"

id: wifi_strength

device_class: "signal_strength"

unit_of_measurement: "dBm"

update_interval: 240s

binary_sensor:

- platform: gpio

pin:

number: 12

inverted: true

name: "Fan Local Control Speed 1"

id: "fan_local_1"

icon: "mdi:fan-speed-1"

filters:

- delayed_on: 500ms

- delayed_off: 500ms

on_press:

then:

- switch.turn_on: speed1

on_release:

then:

- switch.turn_off: speed1

- platform: gpio

pin:

number: 13

inverted: true

name: "Fan Local Control Speed 2"

id: "fan_local_2"

icon: "mdi:fan-speed-2"

filters:

- delayed_on: 500ms

- delayed_off: 500ms

on_press:

then:

- switch.turn_on: speed2

on_release:

then:

- switch.turn_off: speed2

- platform: gpio

pin:

number: 14

inverted: true

name: "Fan Local Control Speed 3"

id: "fan_local_3"

icon: "mdi:fan-speed-3"

filters:

- delayed_on: 500ms

- delayed_off: 500ms

on_press:

then:

- switch.turn_on: speed3

on_release:

then:

- switch.turn_off: speed3

switch:

- platform: template

name: "Fan Off"

id: "fan_off"

icon: "mdi:fan-off"

lambda: |-

if (id(speed1).state or id(speed2).state or id(speed3).state) {

return false;

} else {

return true;

}

turn_on_action:

- switch.turn_off: speed1

- switch.turn_off: speed2

- switch.turn_off: speed3

- platform: gpio

pin: 16

interlock: &interlock_group [speed1, speed2, speed3]

interlock_wait_time: 1000ms

name: "Fan Speed 1"

icon: "mdi:fan-speed-1"

id: "speed1"

inverted: true

- platform: gpio

pin: 5

interlock: *interlock_group

interlock_wait_time: 1000ms

name: "Fan Speed 2"

icon: "mdi:fan-speed-2"

id: "speed2"

inverted: true

- platform: gpio

pin: 4

interlock: *interlock_group

interlock_wait_time: 1000ms

name: "Fan Speed 3"

icon: "mdi:fan-speed-3"

id: "speed3"

inverted: true

It is important to note that the GPIO for controlling the relays are interlocked. There is also a 1000ms delay between switching different outputs on. This is to ensure that the relay are actually switched off, and to prevent energising more than one motor winding at a time.