Introduction: Light Jar - Hall Switch Activated
Jars with led lights... these have been around for a while. There is a jar with light inside, the cool thing is that you can even design a scenery inside to make it a cool lantern or an ambient decoration in the room. Dig the web and you can find some awesome ideas for it. The common problem with all of these is the ugly switch or electric cord sticking from the lid. Today we are going to eliminate this problem and make a clean jar with led light inside with nothing sticking out.
My intention here is to present the technical side and simplify it, while you keep your focus on the creative side and design your awesome scenery inside the jar.
Hall effect 101 - a voltage is produced when you subject a conductor to a magnetic field.
Why is this important? We will use a switch that uses this effect, see the attached video. There are two types of these switches: the regular one - will stay in the ON state as long as it is subjected to a magnetic field, The latching one - it will latch it's state while subjected to a magnetic field. The last one is more interesting and this is the one that we will use as it allows for a more "magical" result.
Step 1: Parts List
First of all you will need a jar and an idea for your inside world/scenery. I'm leaving this to you.
Next, these are the parts we will use for our small project:
1. PCB proto board, this one is really nice:
It is the same from here:
2. LED, I used the following:
But, really the sky is the limit, aim for something you like, make sure it is suitable for one cell.
3. Resistor, we will need one around 100-300 ohm, or an assembled equivalent. I've found this set which should be suitable for lots of projects:
4. Hall swith, here is the latching one:
And the regular:
5. Battery. I used this one:
If you need smaller, there is this one:
If you want even smaller, you can get it from your not in use/broken/old/not needed Bluetooth earpiece. Just be careful and don't short circuit it too much :).
6. Every battery needs charger. This one is suitable directly for the battery I used:
If you want something simpler and comfortable with fitting your own connectors, then this one is for you:
7. Male pin strip - regular one with standard spacing, I'm sure you have leftovers from somewhere.
8. Small rare earth magnet, for the magic stick, like this one:
Let's get started.
Step 2: Schematics and Board/Parts Prep
The circuit is really simple, see the attached picture.
Cut the board to 4 by 6 holes and you are done prepping.
Step 3: Solder the Three Top Components
Solder the male pins and the led separately to the board, positive leg of the led is marked on the picture.
Insert the resistor and solder in. Connect with positive led at one side and positive pin on the other side.
Clip the legs.
Step 4: Solder in the Hall Switch
Bend the legs of the unit as shown. It will go on the copper side of the board - as close to the lid as possible.
Solder as shown. Note that the middle leg will connect the negative led leg and negative pin.
Clip the legs.
Step 5: Solder the Battery, Glue in to the Lid, Make the "magic Stick"
Solder the battery leads to the board besides the exposed male pins. The pins will be used to charge the battery without detaching it. The circuit is ready.
Hot glue to the lid.
Make the "magic stick" - this is simply a small rare earth magnet glued on a stick/pencil. I didn't have one nice and round, so I used a piece of a larger magnet I had lying around.
Now, here is the difference between latching and non-latching hall switches. For latching you will use the magnet-on-a-stick to turn it on/off, see video. For non latching the magnet heeds to be on the lid all of the time for the light to stay on. So, you may want to leave it as is with no stick for this option.
Now, you have your light! It is time for the really cool scenery inside the jar.
6 years ago
Such a hidden switch can be a cool feature, but you're using it in a very strange (and wrong) way. I've attached a schematic of how it should be connected :)
As you have it connecteed, you have the LED on when the Hall is in its passive (off) state and then you shunt the LED, but keep a higher current flowing when it's active (on), as it pulls current through the resistor to ground through the (open collector) output transistor, with the LED off, giving a current drain in either state.
Besides, the Hall will drain around 5mA idle (when connected correctly) and then comes the LED current - if you use a reed switch instead, you can get the same function with zero current drain when the LED is off and just the LED current when it's on. This will give you a huge improvement in battery life.
Have a nice day :)