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LED nightlight for Sayo 555-based circuit Rate Topic: -----

#1 User is offline   aotsukisho 

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  Posted 19 February 2016 - 05:01 PM

This is a project I threw together for Sayo's gift for Valentine's Day...unfortunately I spent too long building a circuit that ended up not working (link). The output would pulse one good one, and then the remaining pulses were too weak to get decent brightness out of the LED.

I decided to scrap that one altogether, and use a different circuit (link). A sine wave is the end result I was trying to get anyway, and the good thing about it being used to just control an LED is that the exactness of the waveform doesn't matter. If it ramps up gently up and down more than an on/off I will be satisfied.

This was done over the course of around ten or twelve hours, spread out over the course of a week or so.

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The first thing I needed was a base, something that would be large enough to fit the pcb yet have a surface up top to diffuse light. Fortunately I had these laying around, they are broken Skylanders portals. It was a perfect enclosure for the project, seeing as it fit all the criteria and even had an integrated power source that was viable for use with the 555 chip (5v over USB).

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Flip them upside down and you can see their feet

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Rip out the feet

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Unscrew these four to loosen the base from the rest of the body

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This is what it looks like inside. Just like I thought, the actual PCB is very small. The wire ring up near the top is the antenna that reads the NFC chips inside the figurines.

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Popping off the top with some tabs, and you can see the entire structure

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Small Philips head screws inside here separates the lid from the body, there are four of these as well

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Closer look at the PCB, remove the two screws on it in order to take it out

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Here's the board underneath.

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Here's a piece of my protoboard that I've broken in order to fit the project dimensions, and weirdly enough its mounting holes line up exactly with the ones in the portal.

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Single shot of my solderwork underneath, all the empty pads covered in solder were from the failed circuit that I scrapped. The excessive length jumpers were also from the original circuit.

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Testing the circuit, and thankfully it works. The 50k pot is to adjust the speed of the 'breathing'.

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The PCB is screwed in and secure in the portal chassis.

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Closeup of the other side of the circuit, the long resistor lengths were just so the LED could be mounted roughly in the center of the chassis.

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Testing the circuit with the shell put back together. Thankfully it still works, so I filed down the top of the LED by hand in order to slightly improve the light dissipation. Ideally the entire surface would light up equally, but it's just not worth the extra complexity...and I have to keep the current draw as low as possible.

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Finally put back together and finished. I left out the green ring, partially because it looks better without it, and partially because I'm not sure if things will get warm in there seeing as there is a transistor driving a 100mA LED.

Not sure if you can make out the schematic as it's slightly blurry, but it's straight off of the 555 sine wave generator page just with a few differences:
  • 100nF capacitor on pin 5 removed since it was unnecessary
  • R1 (timing resistor) changed to a 50K pot since I had them laying around
  • C1 (timing cap) changed to 100uF in order to squash the oscillator frequency down to the range of 0.2Hz or so. The circuit was originally designed to run at 27KHz.
  • Output was coupled to a 2N2222 through a 62K resistor. LED limiter resistor is 110ohm I think.


I took a video and put it up on Youtube here:


I hope she likes it!
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