book collections email follower instructable user
Picture of Hall (effect) Log Lamp

A couple of years ago we decided to have a winter holiday in Scotland. We just wanted to get away for a little while and possibly find some snow. Unusually for the time of year our days where fill with sunshine and blue skys.

We purchased some logs for the wood burner but didn't use all of it so we decided to bring home what we had left. This one log was placed by the fire at home and for some reason we could never bring ourselves to burn it. The weeks turned into months then we moved home and the log from Scotland came with us.

I decided some months ago that it should become a lamp otherwise it would just sit by the door forever gathering dust. The original plan was somthing simple with a base and and top but as is often the case once the project started the design evolved quickly into somthing a bit more dynamic.

The brightness of the lamp changes depending on how open it is. When its closed the LED is off. The wider open it is the brighter it is.

The effect is achieved by using a magnet and a hall effect sensor the output of which is fed into a micro controller that drives a PWM input on a 350 LED driver board. The whole system runs on 5 volts and draws less than half an amp at full brightness.

Parts List:

  • ATTiny 85 Micro controller (plus your preferred system to program it)
  • Arduino Uno for calibrating
  • Minature ratiometric hall effect sensor (SS495A)
  • 350ma LED Driver DC-DC (ebay search for: 350ma dc led driver pwm)
  • 1w warm white LED on star PBC
  • Heat sink for the LED
  • Selection of wires
  • USB cable
  • Hinge
  • DIP 8 IC socket (optional)
  • Prototyping board (optional)


  • axe
  • power sander
  • router
  • saw
  • hole drilling bit
  • power drill
  • chisel & hammer
  • soldering iron

Why I chose these parts

I choose the ATTiny 85 as the micro controller due to its size and low power usage, it also has more than enough IO pins for this project. It can be programmed with the Arduino IDE and its just so cute!

The SS495A might have been the wrong choice for this as its bipolar and so possibly has a more limited range of output when used in this way to what a unipolar might. However when I was researching hall effect sensors I found a video that demonstrated this one doing what I needed it to do, its also very small and cheep.

The LED driver I already had but what I still like about this type is thats its a step down driver and only needs about 1v over the forward voltage of the LED to work. As we are supplying 5v and the LED only needs 3.4v it perfect. Its also small has PWM dimming and again is cheep.

The LED really is personal preference. 1W is plenty bright enough to give a nice background light to a small room or hall way. They don't generate too much heat and come in a wide range of colours. You could just buy the LED with out the star PCB but it makes them much easier to attach to a heat sink.

The heat sink I have used for the lamp might be a little bit of over kill for a 1w LED however as its fitted into wood (not a good conductor of heat) I though it best to go too big than too small and have the LED burn its self out.

Step 1: Splitting, Sawing, Sanding, Routing, Drilling

As this is a unique piece of wood I think it was be best to tell you how I worked it to achieve the end result and will move onto a more conventional Instructable style once things become more repeatable.

As the log had dried out a natural line opened up so it was the obvious place to split it using an old axe and piece of wood drive the axe in. the log came apart relatively easily and the bark mostly just fell off.

I used a hand saw to cut down the length of one of the pieces to create a flat bottom then spent a couple of hours sanding with the belt sander to get everything tidy, flat and smooth.

The router came out next and I routed out a recess in the bottom of the bottom piece for the electronics. I then routed a channel in the top piece to accommodate the support arm.

I made the support arm from the off cut by splitting it and sanding it into a round stick(for want of a better word)

I marked the location of the hinge, the magnet and hall effect sensor with a pencil and used a chisel to cut the recess for all of them. The magnet need to be very close the the Hall effect sensor when the lamp is closed and not more then about 75mm away when open ( I will go into more detail later about the sensor and magnet)

Using the adjustable hole cutter on the power drill I bored out a space for the LED heat sink to fit into then drilled a hole diagonally into the channel for the wires to run. I also drilled 2 holes through the back into the bottom recess for the power in and LED out and one hole in the top piece that lined up with the channel for the support for the LED power wires.

Working out where to place the steps for the supporting arm to sit into was a case of cutting out a little bit at a time with the Dremel and testing to find the right height for each step.

Then stick the magnet on place with a drop of glue.

Oh, I love this! I've never seen a log lamp like this. It's really pretty! :)

jumbleview1 year ago

Nice. The idea to shine more as something is opened wider is very attractive. I may steal it for my some future project. And I should learn more about the Hall effect sensor.