Philips Hue – simple relay hack

img_20170102_162008OK, so I said I’d start simple but this is about as simple as it gets. I’m almost embarrassed it’s not a little more complicated. I’ve done a teardown of a LBW010 bayonet fitting bulb and thought I’d take a look at its E27 screw-in cousin. (I’ll post this teardown later, but here’s a photo to give you the gist of it.) You can see the main board in the centre and the LED board that I’ve removed. It was similar to the B22 but quite different too.

Coming in from the left in the main photo below are the Hue mains connections – blue neutral and red live. My apologies about the mixed colour schemes but those were the wires I had to hand. Heading out on the right are the positive (red) and negative (black) that normally run to the LED PCB. All I’ve done is connect these directly to the input of a solid state relay. That’s it.img_20170104_212708

So why is this hack a little blunt? Well the four wires you see that aren’t connected are my far more sophisticated attempt to dig out some useful logic signal from test point on the PCB. There’s some nice stuff there. I thought I’d use a PWM output I found on TP5 to drive the SSR. It was almost enough but I hit a small snag. (Currently it works as expected between 1 and 100% but irritatingly switched the SSR on when at 0%.) I thought about leading these to a logic circuit, maybe even another microcontroller.

Then I saw the 3-32V input on the SSR. 32V?? That’s a little bit more that the Hue puts out the the LEDs. Could I? Yes, I could. The Hue outputs are used to driving 260mA at about 31V so with minimal load it actually reached about 37V, but it seemed to work fine. I’m using a constant current driver to drive a low impedance and just getting lucky that the voltage limit is being hit. I know that’s not sensible.

So basically , rip the bulb apart, connect it to a SSR and you can now drive any mains lighting you like! It should work with the B22 and maybe even the GU10 bulbs too, but these single colour bulbs are the cheapest.

Things can certainly be done a little better and it will be. For instance:

  • I could use a voltage divider to tame that 37V a bit.
  • I could drive a normal relay if I added a  suitable series resistor and a flyback diode. SSR have problems driving some loads – ironically LED drivers being one of them.
  • I could dig further into that PWM signal and properly detect the power level of the light, maybe driving more than one relay or SSR.

Anyway, all this will come but I thought this simple hack was worth sharing as-is.

UPDATE: A better way to get to a decent signal to control anything (using a B22 bulb) here.

Philips Hue garden floodlight

So, after the initial teardown, it’s time to start the Philips Hue hacking. To be honest this is fairly simple so doesn’t really qualify as a hack. I said I’d start small and work up from there, so consider this a warm-up exercise.

I’ve got a motion sensing 10W LED floodlight mounted on my workshop. It’s supposed to light my way as I head out there but it doesn’t really work as I’d like. As I’m walking straight towards it the PIR only triggers when I’ve already trudged through the dark garden and I’m about a metre away. Also, the local foxes are constantly triggering it at night. Having this under Hue control would be ideal. Let’s take a look.

img_20161231_130126My Wicked brand floodlight contains a single chip LED which actually had 9 separate LEDs on the die. It has a constant current LED driver which outputs 350mA at about 24V. Hmmm – this could be very easy. They pretty much matches the Hue bulb I tore down. Electrically this might be as easy as connecting the spotlight’s LED in place of the Hue’s board. And you know what – it was! I did a quick check that the hue bulb circuitry was happy to dive the LED in the floodlight directly and then it was just a case of putting it all together. Out came the PIR sensor. Out came the constant current LED driver (the white box) and in went the Hue circuit board.

img_20170102_130311The only tricky bit was deciding where to put the PCB. Once the LED driver had gone, there was plenty of room behind the light. However, this was a metal case and the light is a fair distance away from the house. I didn’t think the Zigbee signal would reach. It didn’t have to be in the lamp at all of course, but it seemed neater.

I decided that the best place to put it was where the PIR has been. All it needed was a new 3D printed front cover. I could have saved space and printed a new back piece. I could have missed out the hinged bit and printed a two part case. My new Year’s resolution is to get project finished so I went with the simplest option.

img_20170102_131430So, here it is side by side with an original. Fitting was pretty easy. The only gotcha I has was that as i connected it, the Hue hub decided it would be a good time to update the firmware in the bulb. Hue bulbs normally switch on when first powered but whilst updating it was off. Cue some unnecessary checking of wiring, removing and remounting it, checking fuses, etc. Oh well, it working


Philips Hue LBW010 teardown

Why Hue?

I’ve been thinking about some how automation for a while but have been wondering how the best way to go about it would be. I was thinking of a mesh network of battery powered switches using Sub-1GHz 6LoWPAN – hence the recent mucking about with Contiki OS. However, I decided to go for a couple of Amazon Echo Dots in a recently Black Friday promo and decided that I should get an off-the-shelf solution working whilst I spend the next couple of years making the “perfect” one.

After a little research I decided on the Philips Hue system. These are Zigbee controlled bulbs that you leave permanently powered. The system isn’t perfect – but better than the others on the shortlist. Z-Wave is proprietary. LightwaveRF leeches power through the bulbs and you can’t tell if the device heard your command or not.

Philips did get some grief for locking out other Zigbee devices but seem to have reversed that. Obviously other devices don’t quite get the love that Philips products do, but they’re OK. On the plus side, Philips have documented a nice API at the hub level that allows you control their bulbs from the outside of the Zigbee network. They are however understandably protective of things on the inside.

On the negative side, Philips do not have a device that can control an arbitrary light. I’ve got a floodlight and some track lighting in the workshop. Can’t do those. My bathroom has about 9 GU10 bulbs in the ceiling – possible but 9 x £25 is an unpleasant £225.

What’s the plan?

My plan is threefold.

  • Firstly, I want to take one of the cheaper £15 single colour bulbs apart and see what’s what.
  • Secondly, I want to extend the Hue ecosystem but by “gently” hacking it – i.e. buying a Philips Hue product, leaving their hardware and code more or less intact but adding what I want to it.
  • Thirdly, I’d like to do some Zigbee work. Maybe make a slightly more feature rich switch that those they supply. Maybe vreate a Zigbee light that Philips are happy to work with

Anyway, I’ll start with the simplest so I have something working and take steps from there.

What’s inside then?

img_20161209_174552Before I start, let me say that I was greatly helped by the work of others such as Colin O’Flynn. I’m not the first to tear open a Hue bulb, but it turns out my UK spec bayonet fitting LBW010 is a bit different to those before.

First you have to remove the plastic top. I used a small hacksaw, but it eventually came away in one piece when the glue gave way. I think a little bit of squeezing in the vice might have been all that’s needed. It’s not like I’m going to put it back together anyway so not too important.

img_20161209_174841It opens up to reveal the LED board (with metal heatsink) which is attached with a couple of screws and more glue. I tried a heat gun to soften the glue but that didn’t help. In the end just some levering with a small screwdriver did the trick. The LED board separates nicely from the logic board and has a simple 0.1″ pitch SMT header for this. Very useful. Some quick measurements show the LEDs have a voltage of 24.4V and a current of 350mA. I assume there’s a constant current supply on the PCB but I’ve not taken the time to track that down yet.

One thing worth noting on the B22 bulbs is that the two main contacts for mains power are actually solder. Before pulling the PCB out you should melt the solder on these. I didn’t and ripped on of the 15Ω resistors that are used as fuses from the PCB. Easily replaced, but annoying that I was heavy handed with this.

hue-pcb-bottomOther bulb teardowns revealed an Atmel ATMega2564 (AVR microcontroller with Zigbee) and a ST HVLED815PF (LED driver) but my bulb seems to be different. Inside is an Atmel SAM21R21E18A – the same ARM microcontroller with Zigbee as found in the Bridge. I couldn’t find a LED driver IC so this is perhaps constructed using discrete components. I didn’t look very hard though. I will try to get a better photo later.

There are a number of test pads. Careful probing a track tracing shows they are as follows:

TP2 – PA30 on the microcontroller. This is SWCLK for debugging
TP3 – PA31. This is SWDIO for debugging
TP4 – Serial TX (more on this below)
TP5 – Serial RX
TP6 – main output to the LED
TP7 – 3.3V. This is the output from the 3.3V regulator and input to the microcontroller. It can be used to power the board but you’re better off using TP25.
TP8 – RESET for the microcontroller
TP11 – GND
TP25 – Power in to the LM2204 VLDO regulator. It takes about 24V when powered from the mains but is happy when powered with 5.1V from USB for hacking about.

What was most interesting initially was the output on TP4. It contains debug messages from the Atmel Zigbee stack and on power up you get something like this. Output is 115200 8N1 and line endings are CR only.

[Log,Info,S_LightConfiguration,Configuration Data OK, crc=0x60083D2F]
[Log,Info,S_DeviceInfo,Default Flux table]
[Log,Info,S_DeviceInfo,ProductId: Philips-LWB010-1-A19DLv3, ModelId: LWB010]
[Log,Info,S_DeviceInfo,ZLLDeviceId: 256(DimmableLight), PwmChnl: 1]
[Log,Info,S_DeviceInfo,Booting into normal mode...]
[Log,Info,S_DeviceInfo,DeviceId: ConfLight]
[Log,Info,ConfLightLamp,Platform 0.85.0: r19111, BC_V3.3.0_2.4_M: r19111]
[Log,Info,ConfLightLamp,Product version ConfLight fw_ver: 1.15.0_r18729,built by LouvreZLL]
[Log,Info,A_Commissioning,NwkAddr: 0x32BE, Ch: 20, Pan: 0x5DE4, NwkUpdId: 0, ExtPanID: 8D80F343023D3B9E]
[SYS,Info,Transmit buffer full]
[Log,Info,N_Connection,Starting discovery for updated networks]
[Log,Info,N_Connection,Discovery for updated networks completed]

This is interesting and my initial thoughts were that I could capture any output when light levels are set and make use of these. Unfortunately, there’s nothing interesting once the bulb is connected and running.

hue-pwmI decided that there must be some more useful output from the microcontroller going to the LED drive circuitry so decided to probe the pins whilst changing output. Bingo! It seems that we have a nice PWM output on PA17 with the duty cycle representing the brightness.You need to move a large electrolytic capacitor out of the way to get to the IC and it’s pin 18 (the second one up from the bottom on the RHS). I haven’t traced it to a test point or other more accessible location yet, but I will.