Well why indeed, Well why not!
This project has 2 distinct appeals to me.
1) For me, it does jazz up a very plain area of the house. It also does it in a way that is unique (I'm not aware you can buy this sort of thing from the local hardware or electronics shop - not yet at least),
2) There is a practical and safety element too here.
Practical - The hall and stairs a frequently used but only need to be lit whilst you walk up/down them. You can switch the lights on and off each time but even the energy miser that I am I forget sometimes to switch the off only to realise hours later that they are still on.
Safety - As this system is automaticaly switch on via passive infra red detectors (PIR), it might save a fall down the stairs at night if, either you risk walking down with the light off or someone unfamiliar with your house stumbles down because they can not find the wall switch for the lights
In this regard this project could also be installed in other 'traffic' areas of the house, particularly dark corridors whith little or no natural light.
Step 1: Safety Notes
Whilst all the circuits you need to wire and construct are 5VDC and (as such are catagorised as extra low voltage) you are ok to work on a project like this with no electrical license. However I would point out the following notes:
1) You will need to get that 5VDC from a power supply connected to the mains. The easiest is to use a power supply with an already terminated plug. However, I decided to wire my system directly to a lighting circuit as it was the most convenient power (closest) to suit my needs. Get help with this step is you are not confident or competant - mains electicity can be a killer!
2) The DC ampage (amount of current) for this project is not insignificant. Make sure the 5VDC cable has conductors of sufficient cross section (thickness). A cable that is too thin could heat up and potentially cause a fire, although this is a worse case scenario I thought should just mention it.
Step 2: Tools and Skills
I have tried to make this project achievable by the typical DIY person. Most of the project is to wire together bought components and construct a fairly simple DC circuit. The most challenging issue is to get access to install the wiring in and around the stairs, in this regard, the higher your skills and patience are the better the outcome
For the Wiring:
Soldering Iron - only a low skill level required.
Drill - to drill holes in stairs for wiring.
Crimper and spade terminals for wire terminals - depending on how you terminate to the small control board
Multimeter - not absolutley necessary but an invaluable part of your toolbox if you plan to do more projects of this type!
Hammer - for cable clips
You will need a computer with a USB connection and the Arduino IDE loaded.
Programming skills - not really required if you just download my pre-prepared program. However the more familiar you are with Arduino the easier this instructable will be to understand and you could modify the lighting schemea and or timings.
Step 3: The Basis of the Project, an Adressable LED
Rather than use the common type of RGB (Red, Green, Blue) LED strip, this project uses a strip utilising WS2821B LED's. These LED's which come in a 5050 package (thats 5mm x 5mm square), have an additional 'inteligent' chip incorporated into each LED which allows it to be switched on independantly of the other LED's in the strip. This allows the user full, open and flexible control of the light and colour which is in stark contast to the sometimes garish FLASHING that LED strips can sometimes feel like.
I've added a PDF datasheet for the LED but this is just for your further interest and you do not need to read it to complete this project.
Step 4: The Circuit
Here is a Fritzing circuit diagram. I had to improvise the PIR parts as they are not in the library, I hope this does not cause any confusion.
Step 5: Powering the LED String
The LED chip string chosen for this project requires a 5VDC power supply. The current draw for these strips at full blast (RGB all on, eg white in colour) and at full brightness is as follows:
30LEDs/meter ~9 watts ~ 1.9amps @ 5VDC
60LEDs/meter ~18watts ~3.8Amps @5VDC
There are strips with higher number of LEDs/meter, right up to a whopping 144/meter but I think that that is a tad over the top for a bit of ambient background lighting such as this project.
I decided early on to use the 30LEDs/meter strip and as my staircase is 3.9 meters long I can expect the system to draw:
3.9 x 1.9 = 7.4Amps - thats quite lot. However, for the most time the strip will be running at much below this maximum but the system should be designed to cope with this peak current.
With this high ampage requirement comes 2 issues:
1) 5V power supplies at 10Amps (or 7.4Amps) are not as common as you might hope. I ordered one to come from the same e-bay supplier.
2) The issue of volts drop on:
a) The LED strip. If 5VDC is just inputted at one end then there will be a drop in volts due to the resistance of the thin copper strip. The reccomendation is to only power strips from one end for lenghts up to 1 meter. To remedy this I propose to power the strip in 2 mid points, 1 meter in from each end.
b) The 5Vcable itself. The choice of cable is also important to enure that the it has sufficient current carying capacity.
I will deal with both these issues in the next 2 steps.
At the end of this project I will check and verify these figures. See a later step.
The LED strip I purchased came from e-bay
Step 6: The 5VDC Power Supply
Hmmmm so I'm needing a 10Amp power supply.
The options are:
1) The E-bay supplier offers one.
In the end I did not use it in this project as I got hold of another one for free!
2) Here is a link to a frame style power supply, This should be installed in a project box/enclosure which is fine as we will need to have an enclosure for the Arduino, it will just need to be much bigger.
3) "double up" smaller (less capacity) power supplies - I personally don't like this solution but it should work.
4) A bench top power supply - ok for a temporary set up but not really suitable for a permanent installation.
Step 7: The 5VDC Wire and the Wire Routing Scheme
This sounds complicated but is actually quite simple.
I've choosen this wire which I obtained from the local hardware store. It is twin 1.5mm2 stranded copper wire in a white PVC sheath.
The resistance for this wire is rated in the documentation from Olex as 13.6Ohms/km = 13.6/1000 = .00136Ohms/meter. This is the rating for DC use at 20DegC.
If I were to run 5VDC for 5 meters then the volts drop would be (using Ohms law where V=IR)
V (volts drop) = I(current)xR(resistance)
V = 7.4 x .00136 x 5(meters in length) = 0.05V which is nice and low = ok
This is ok but I also understand that for these strips that if you feed in the power only at one end then the LED's at the other end will be dimmer.
To get around this issue you can feed in the DC to multiple points on the LED strip - as per the diagram above
Step 8: Install the 5VDC Wiring
If you have access under the stairs as I did it makes the installation much easier. If you don't I suggest you hide the cabling along the edge of the carpet and find a location for the controls at either the top or the bottom of the stairs. The location of the nearest 240/110V AC power will probably dictate the best location.
Install the 5VDC wire to the 2 locations on the stairs.
- Pull the carpet to one side to reveal the staircase itself.
- Drill a hole in the riser and thread the wire through to the underside of the staircase.
- Use a couple of cable clips to keep the cable from creeping or slipping.
- Replace the carpet.
Step 9: Install the LED Strip
Starting at the top of the stairs lay the strip out and then fix it in a suitable position along the stair treads. In my case there was a convenient lip to hide the strip under. In my opinion it is better to have indirect illumination in this case so the more you can 'hide' the strip the better (as long as the light comes out and illuminates the treads of course)!
The strip is held in place with a combination of plastic clips and the odd dot of superglue.
Step 10: Solder the 2 5VDC Power Feeds
Now it is time to solder the 2 x 5VDC power feeds. In my case the LED strip is encapsulated in a plastic square sectioned tube so it is necessary to carefully cut a small window in this area so that you can get access to the solder pads. After soldering I covered the joint with masking tape which happily is a similar colour to the carpet and paint!
Step 11: Install the Wiring for the 2 X PIR's
2 PIR's need to be installed. One at the top of the stairs and one at the bottom. The PIR is used to detect motion in the same way tht a burgler alarm senses an intruder. The way PIR's work is that they constantly monitor the background infra red radiation (heat). When you move in front of the sensor you change the 'view' that the sensor has and an alarm can be triggered.
Each PIR sensor has requires 3 wires.
2) 0VDC Ground
3) Signal wire
In my installation I used old spare cable I had in the garage, if I were to purchace cable the following cable would be suitable.
Basically any 3 wires should be ok as the current consumption of these PIR's is very low and so there is no requirement for thick heavy cable.
Currently I have not mounted the PIR's satisfactorily. I was wanting work out the best angle to set them to before finally fixing them in position. It would be nice to have a 3D printer to make a specialised mini housing!
Step 12: Install the Light Dependant Resistor (LDR)
Install the LDR in a position where it can detect the ambient light but will not be affected by either:
1) The LED's when they turn on or;
2) Any other light that may be installed in the hallway
I installed the LDR on the outside of the stair treads - its a pretty inconspicuous position and there is no hallway light near this location to intefere with the operation.
You could omit this feature if you are happy for the LED's to work 24/7. A minor change in the Arduino program would also be required. If you do include this then you will probably need to adjust the cut in/cut out point. Again this is a simple change to the Arduino program.
Step 13: The Arduino Controls
As I mentioned in the introduction this project is controlled by an Arduino. If you are unfamiliar with Arduino it is a the name given to a family of microprocessor based (Atmel AT Mega) printed circuit boards made to enable you & I to make projects that interface with the outside world.
The software used to drive these microprocessors is based on C++ but you will not need to learn how to use this as I've provided the code in a later step and all you will need to do is download it to the board using your PC (via special USB cable).
I decided to use this Aruino board, the Arduino Pro Mini (5V 16Khz Version)
This is a rather small board and in designed for use in semi-permanent installations and does not include a USB port on the board. If you are a newcomer to Arduino you may want to use a more "full Size" version such as the "Uno" or the "Micro"
As Arduino is "Open Source" you can either buy official hardware or clones from all sorts of sources. The choice is yours. I've used the one available from Sparkfun - around $10USD
Step 14: Mount the Arduino on a Small Piece of Perforated Board
Firstly I mounted the Arduino board onto a small piece of perforated board - This allows the field wiring to be easily interconnected and the board mounted into an enclosure.
1) I added an 8 way female header from Pin 13 to the GRD pin on one side of the Arduino
2) I added 6 male pin headers to the end of the board to ease programming
3) I supported the Arduino on the perf board with 3 x 2 pin headers in these locations.
pins 10 & 11
pins 6 & 7
pins tx & rx
Step 15: Add Some Headers and Other Connections
I added 4 x 2 pin connectors onto the perf board
1) for 5VDC power input - this is to power the Arduino Pro Mini and the 2 x PIR sensors
2) & 3) for the PIR sensors
4) For the Light Dependant Resistor (LDR)
I added a 10k 1/8w resistor to act as a small current source for the LDR for the analoge input. (If the LDR has high resistance (when dark) the analog pin will be at 5 Volts).
I had the resistor already - you should be able to get one at your local electrical hobby shop - here is a link to a pack if ths helps:
Step 16: The Arduino Software
Here is attached the software for the Arduino.
The software is extensively commented so should be easy to read - so go ahead and check it out.
The function of the software is as follows:
When one of the Passive IR sensors the LED's will light up in the direction of travel - either up or down the stairs
After a period of time the lights will extinguish (again in the direction of travel). The LED's then display a 'waterfall effect' for a period of time ~30 sec then fade out.
In idle the first and last LED 'breathe' to show the program is looping.
The I/O is as follows:
Pin 6 output for LED strip
Pin 10 input for PIR at the top of the stairs
Pin 11 input for PIR at the bottom of the stairs
Pin 13 output for Arduino on board LED (for debugging)
A0 for Light dependent resistor.
Step 17: Loading Up the Software From a PC
As I used a Arduino pro mini I needed to use a special programming converter to load the program up to the board.
This is what I used:
Of course if you have choosen to use an Arduino that already has the USB connector on board (such as the Arduino Uno) you will not need this and you can go ahead and load the program straight away.
1) Connect your PC/MAC to the Arduino over USB
2) Open the Arduino program IDE on your PC/Mac
3) Make sure you pick the correct board type and serial communications port under the "Tools" menu
4) Open the file provided in the last step
5) Press the "Upload" button - you should see the tx/rx led's on the Arduino board flicker for a few seconds as the program is uploaded.
That all - you can disconnect everything now and the programme is retained on the Arduino
Step 18: The Installation Under the Stairs
I have used a small polycarbonate box and, well, in fact it was too small but I had it lying around and it just about fits!
I added a fuse on the inbound 5VDC - it is currently a 10Amp one but I may reduce this later.
I also added a 16V 3300uF electrolytic capacitor as recommended by the good people at Ladyada (they actually state 1000uF 6V or higher).
Here is a link for a 1000uF capacitor.
Step 19: Actual Current and Power Consumption
Amperage in use:
Initially, I measured the DC usage at the 5VDC input so it does not include the efficiency of the power supply itself.
1) Idle = 0.152A = 760mW
2) All on (warm white) 0.857A = 4.285W
(In testing and setting up I discovered that I did not like the LED's (Fully on at '255'. I actually used 50, 50, 30 for R, G ,B settings to give a warm white colour).
3) all on (full blast, ie 255,255,255) = 4.036A = 20.18W
(4.9A is less than I calculated in step 4, (7.4A) . I'm not sure why there is such a wide discrepancy. Any ideas?!
To do a further check I decided to test the AC current into the power supply
1) All on (full blast, ie 255,255,255) = 0.139A = 30.0W (assuming power factor of 0.9)
2) Idle = 0.037A = 7.992W (no photo)
Clearly I could have used a much smaller power supply. Given the power supply is using about 8W in idle it may be better for me to swap this out at a later date. (8 x 24 = 192Whrs/day) = 70kWhrs/Year. Depending on your cost of electricity (curently 51c/kWh for me at peak rate) will alter your opinion on this issue!
Step 20: Conclusions and Comments
So....whether you have a grand staircase with chandaliers or just a simple ladder, you can add a unique feature and get those LED's guiding your way in the dark!
As always comments and suggestions for improvements are most welcome.
Kawajohn made it!