Here’s a clever idea I saw on Instructables. If you have kids then you probably have lots of magnetic things stuck to your fridge (if you don’t have kids the get with me offline, you can have some of mine). Just kidding. I’d never solicit something like that. Publicly, I mean.
Anyway, back to fridge magnets. In this Instructible the author has created LEDs that stick onto a power grid on your fridge and light up. The way the author creates and powers the grid is clever, although I’d try something different on my fridge. The author uses conductive spray paint and masking tape to spray paint the power grid directly onto the door of the fridge. The grid is powered by a 4.5V AC power supply, which is attached to the grid by epoxying magnets to the power supply wires and placing the wires onto the grid traces. AC power means the LEDs light up no matter which way they are placed.
The LEDs have their own magnets that make them stick to the door and contact the power grid. The magnets are tiny 1/8 inch diameter rare earth magnets. The LED leads are bent into small circles, just smaller than the magnets. The magnets are placed into the circles and epoxied into place.
The author uses a mix of 2.4 volt and 3.6 volt LEDs. The 3.6 volt LEDs are connected directly to the grid with no current limiting. This seems OK since they’re operating at less than 50% duty cycle due to the A/C power supply. The 2.4 volt LEDs might also be able to be connected directly, you’d have to check the data sheet I/V curve to know for sure. However the author isn’t taking any chances. Once the magnets are epoxied to the 2.4 volt LEDs he cuts one of the leads and joins the ends together with a 1206 surface mount resistor. That’s a lot of fiddly soldering!
When the LEDs are done, you place them on the grid to the unabashed delight of any kids nearby.
A few things occur to me. First would be to avoid any soldering by using LEDs with integrated current limiting resistors. These are marketed as “5 volt LEDs” or “12 volt LEDs” and have the appropriate resistor integrated right into the LED. These are available in the 25 cent each range in small quantities.
Second would be to use a PCB instead of conductive spray paint. If there are kids around then there’s probably a spouse around also, and a spouse may not approve of painting the fridge. The grid could be etched onto the PCB, and the PCB in turn attached to the fridge with double sided tape or a couple dabs of silicon glue. Once you have a PCB then you have other interesting possibilities, like a display that plays tunes as well as lighting up. You could have circuitry that times out and shuts the grid off after a certain amount of time. The display could automatically adjust to ambient light conditions. With that you might be able to run the whole thing on batteries.
Another possibility is to use bicolor LEDs, which are two LEDs of different colors, connected with opposite polarity to a common set of leads in a single package. This LED lights up with two different colors depending on the applied polarity. This would give you two colors for each LED depending on how it was placed in the grid, assuming you use a DC power supply instead of AC.
You could also try RGB LEDs. Maybe a careful arrangement of LED leads accompanied by multiple power grids with matching spacing would give you many different colors depending on the rotation of the LED.
Lots of ideas for experimentation. If you have any ideas leave them in the comments section below. And if you’ve seen, built, or heard of any interesting gadgets let me know and they may be featured here. Actually, if you’ve built a gadget then you should consider submitting it and possibly getting paid for it.
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