A $6 internet of things and easy to build motion detector.
This implementation controls a Philips Hue light, but any IoT application can be implemented using the builtin WiFi adapter.
| Name | Type | Price (USD) | Link |
|---|---|---|---|
| WeMos D1 mini V2.2.0 (ESP8266 board) | Microcontroller | 4.09 | banggood.com |
| HC-SR501 | Motion detector | 1.95 | banggood.com |
Total cost: USD 6.03 (excluding shipping, recorded 2017-09-16)
- Jumper wires
- Breadboard (prototyping)
- Soldering iron
- Micro USB cable (system power/ESP8266 programming)
- USB power adapter (system power)
- Computer (ESP8266 programming)
See http://henrysbench.capnfatz.com/henrys-bench/arduino-sensors-and-input/arduino-hc-sr501-motion-sensor-tutorial/. It is recommended to set the time delay to the minimum as the software handles delays itself.
The values in this section are calculated, I do not have the required hardware to make measurements.
Sensing for motion, not sending/receiving over WiFi.
| Component | State | Power Draw (mA) |
|---|---|---|
| ESP8266 | Modem-Sleep [4] | 15 |
| HC-SR501 | On | 0.065 |
Total: 15.065mA
Sensing for motion, sending/receiving over WiFi.
| Component | State | Power Draw (mA) |
|---|---|---|
| ESP8266 | Tx 802.11b [4] | 170 |
| HC-SR501 | On | 0.065 |
Total: 170.065mA
You can quite easily build this project with other ESP8266 boards and motion sensors other than the HC-SR501. When doing so, watch out for the following possible differences (list not complete):
Different ESP8266 board:
- No USB connector (power delivery, programming)
- No 5V output (power delivery to HC-SR501)
Motion sensor other than HC-SR501:
- Required voltage (power delivery)
| Name | Type | Default Value | Description |
|---|---|---|---|
| light_on_duration | uint32_t | 60 * 1000 (60s) | Time to keep the lights on in milliseconds |
| nighttime_start | uint16_t | 23 * 60 (23:00) | Start of nighttime in minutes since midnight |
| nighttime_duration | uint16_t | 7 * 60 (06:00) | Duration of nighttime in minutes |
| hue_ip | char* | - | Local IP Address of the Hue Bridge |
| hue_port | uint16_t | 80 | Port of the Hue Bridge API |
| hue_timeout | uint16_t | 10 * 1000 (10s) | Timeout for requests to the Hue Bridge in milliseconds |
| hue_user_id | char* | - | ID of the Hue Bridge user for authentication* |
| hue_light_identifier | char* | lights/1 | Identifier of the Hue light/lightgroup to control |
| hue_command_on_daytime | char* | {"on":true, "bri":254} | Command to turn the Hue light on during daytime |
| hue_command_on_nighttime | char* | {"on":true, "bri":1} | Command to turn the Hue light on during nighttime |
| hue_command_off | char* | {"on":false} | Command to turn the Hue light off |
| wifi_ssid | char* | - | SSID of the WiFi network* |
| wifi_password | char* | - | Password for the Wifi network* |
| wifi_timeout | uint16_t | 15 * 1000 (15s) | Timeout for connecting to the WiFi network in milliseconds |
| ntp_host | char* | pool.ntp.org | Hostname of the NTP server |
| ntp_offset | int32_t | 0 | Offset from the UTC time in milliseconds |
| ntp_update_interval | uint32_t | 24 * 60 * 60 * 1000 (24h) | Interval of system clock synchronisation with NTP server |
| baud_rate | uint32_t | 115200 | Baud rate for serial communication |
| pin_status_led | uint8_t | [LED_BUILTIN] | Pin number of the status LED |
| pin_motion_sensor | uint8_t | 5 | Pin number of the motion sensor (data pin) |
| motion_sensor_init_duration | uint32_t | 60 * 1000 (60s) | Time until the motion sensor is ready for the first reading in milliseconds |
| debug | bool | false | Output debug information |
*Confidential information, keep private
The following states are communicated using the onboard LED:
- Initializing: LED is on, blinks once when it is done
- Shutdown: LED blinks 3 times long, then turns off
- Motion detected: LED is on
- No motion detected: LED is off
After powering on the device gets everything ready for operation. This includes connecting to the WiFi network and waiting for the motion sensor initialization. If any of these operations fail, shutdown is initiated. The shutdown reason is logged to the serial bus. The amount of time required for initialization is usually bound by the configuration value of "motion_sensor_init_duration".
The device reduces power usage to a minimum. A power cycle is required to restart. A shutdown can only occur during initialization (see section "Initialization").
When motion is detected the light is turned on.
When motion is not detected for the specified amount of time (configuration value "light_on_duration") the light is turned off. When motion is detected again while the light is still on the timer is reset.
Different on-commands can be defined for daytime/nighttime (configuration values "hue_command_on_daytime" and "hue_command_on_nighttime"). When and how long nighttime is can be configured (configuration values "nighttime_start" and "nighttime_duration"). The light state will not update if it is on during a datime/nighttime switch.
The device periodically (configuration value "ntp_update_interval") updates its internal clock with an NTP server (configuration value "ntp_host"). This is a blocking operation and can slightly delay turning the light on/off.
Information about interrupts, actions and requests are logged to the serial interface (USB port). Additional debug information can be turned on (configuration value "debug").
Board: WeMos D1 R2 & mini
CPU Frequency: 80 MHz
Flash Size: 4M (3M SPIFFS)
Upload Speed: 57600
- Support for OTA updating of configuration values
Project goal: Building a motion detector that can turn on Philips Hue lightbulbs when entering a room.
Shipping prices and durations were calculated for Switzerland.
Selection criteria:
- <= 5$ cost (including shipping and microcontroller integration)
- >= 2m range
- >= 60 degrees horizontal sensing range
- <= 1s detection delay
- <= 4 weeks shipping time
- Easy to use with microcontroller (documentation/tutorials)
- Low power consumption
Evaluated options:
- HC-SR501
The HC-SR501 passive infrared motion sensor satisfies all criteria and seems to be a hobbyist favorite.
Selection criteria:
- <= 15$ cost (including shipping and adding WiFi functionality)
- <= 4 weeks shipping time
- Easy to use with motion sensor (documentation/tutorials)
- Easy to use with WiFi (documentation/tutorials)
- Easy to power (documentation/tutorials)
- Low power consumption
Evaluated options:
- Genuino MKR1000
- Arduino Uno
- Raspberry Pi
- ESP8266
The ESP8266 is the only evaluated option that satisfies the cost criteria, has integrated WiFi and seems to be a hobbyist favorite.
The system should be able to be powered by a single power cable or batteries.
The ESP8266 is powered by a micro USB cable. This enables the use of a USB power adaptor and battery packs.
The HC-SR501 is powered directly with 5V by the ESP8266.
The HC-SR501 initially fired a lot of false positives. Putting a 15k Ohm resistor in the data line seems to have solved this problem (see section "Wiring").
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Similar project: https://www.reddit.com/r/esp8266/comments/5l94gl/motion_control_hue_lights_with_esp8266_and_pir/
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ESP8266 programming: https://hackaday.com/2015/03/18/how-to-directly-program-an-inexpensive-esp8266-wifi-module/
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ESP8266 programming with Arduino IDE: https://arduino-esp8266.readthedocs.io/en/latest/installing.html#instructions
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ESP8266 power consumption: http://bbs.espressif.com/viewtopic.php?t=133
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ESP8266 power saving: esp8266/Arduino#1381
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HC-SR501 configuration: http://henrysbench.capnfatz.com/henrys-bench/arduino-sensors-and-input/arduino-hc-sr501-motion-sensor-tutorial/
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Philips Hue API: https://developers.meethue.com/documentation/getting-started
All references were viewed on 2017-09-16.