More light!
Charly's Column – Hue and Rasp Pi
Since his Trådfri Smarthome article over a year ago, sys admin columnist Charly has been receiving messages from readers with two questions: "Can you do that with the Philips' Hue system?" and "Can this also be done with a normal brightness sensor?" Yes and yes!
In a previous issue [1], I described how I control a smart light in my living room with Ikea's Trådfri system and Linux. The darker it gets, the more I turn up the lights. Around the same time, Martin Loschwitz then explained how he used a Raspberry Pi and a transmitter module to control Hue and other Zigbee devices [2].
Now I'm going to do it again, without the Zigbee module, but I expect to use a Hue bridge, which Martin's approach doesn't need, and because not everyone has a roof-top photovoltaic system, this time I focused on a simple brightness sensor.
Getting Started
First, I discovered the IP address of my Hue Bridge: 10.0.0.8. Then I pressed the button on the bridge and entered the following at the command line:
curl --data "{\"devicetype\": \"huelr\"}" http://10.0.0.8/api
The huelr
string (for "Hue living room") is freely selectable. I got some output like:
[{"success":{"username":"T3VGtGWmFUgJwHufxkudY1bizvqoZMhCSqu1ySwm"}}]
This unpronounceable string is an authentication string, which I have to specify with every call in the future. A (confusing) list of all connected devices is returned by the command:
curl --request GET 10.0.0.8/api/T3VGtGWmFUgJwHufxkudY1bizvqoZMhCSqu1ySwm
If you only need information about lights, you can append /lights
to the command or /lights/1
, /lights/2
, and so on for each lamp. The following command switches lamp 1 to medium brightness (value 125
):
curl --request PUT --data "{\"bri\":125}" 10.0.0.8/api/T3VGtGWmFUgJwHufxkudY1bizvqoZMhCSqu1ySwm/lights/1/state
For the brightness sensor, I used a $2.00 module named BH1750 (online, e.g., [3]). I connected this to the I2C bus of a Raspberry Pi (Figure 1). I used the Zero W model with WiFi – it has to communicate with the bridge.

Cat's Eyes
Raspbian comes with almost everything you need, with only a few packages to add:
sudo apt install build-essential wiringpi i2c-tools python-smbus
The program in Listing 1 reads the sensor in the program I named lux
:
cc lux.c -lwiringPi mv a.out lux && chmod 755 lux
Listing 1
lux.c
01 #include <wiringPiI2C.h> 02 #include <stdio.h> 03 int main (void) { 04 int handle = wiringPiI2CSetup(0x23); 05 wiringPiI2CWrite(handle,0x10); 06 sleep(1); 07 int word=wiringPiI2CReadReg16(handle,0x00); 08 int lux=((word & 0xff00)>>8) | ((word & 0x00ff)<<8); 09 printf("%d \n",lux); 10 return 0; 11 }
If you run lux
, you will see the current measured value for the photo sensor in lux units. Depending on this, you can now control your smart lighting.
Infos
- "Charly's Column: libcoap" by Charly Kühnast, Linux Pro Magazine, issue 202, September 2017, pg. 49: http://www.linuxpromagazine.com/Issues/2017/202/Enlightened-libcoap/(language)/eng-US
- "Controlling Zigbee Devices with the Raspberry Pi" by Martin Loschwitz, Linux-Magazin, September 2017, pg. 76: http://www.linux-magazin.de/ausgaben/2017/09/raspi-spricht-zigbee/ [in German]
- Debo BH1750: https://www.ebay.com/i/292393778070?chn=ps
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