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  • Author Author: scottiebabe
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What's new in fairy tech?

scottiebabe

The first set of fairy lights I purchased a few years ago had a very rudimentary embodiment. Just two AA batteries, an on/off switch, and a string of miniature LEDs on enamel wire.

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I love the simplicity of the design... The design works well enough with disposable alkaline batteries. However recharge cells don't work very well on their own, as their combided state of charge voltage very quickly drops below the forward voltage of the white LEDs.

Fairy Tech 2.0

Browsing at the dollar store today, I found some new fairy lights which included some circuitry on a PCB. What could it be?

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Same general look and feel as before.

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Now included is a three position switch!

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The mysterious PCB

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No sign of an inductor anywhere Disappointed. Just a

- 8-pin MCU?

- Watch crystal

- SPDT Slide switch

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Fairy Tech 3.0

I can upgrade this new set of fairy lights with a boost converter module capable of operating of a single alkaline/Ni-MH cell

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Module based on ME2188 https://file.elecfans.com/web2/M00/64/78/poYBAGMHOg-APsG0AAge4TQOpd0961.pdf 

I bought a value pack awhile back thinking I would receive a selection of different output voltages. Nope, I got a bag of identical modules and each has a nominal output voltage of 5V. So, I added an additional 50 Ohm series resistor to limit the current to approximately 40 mA.

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I am taking a bit of a gamble assuming the MCU is 5V rated. If it gives up the ghost, I'll replace it too.

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All for now.

Parents

  • I bought one of these a few years ago. A simple device, no electronics (apart from the LEDs), just an on/off switch. The lights were quite Christmassy. The main problem was that the springs used for the battery contacts were far too strong. This resulted in the eventual bending-backwards of the end of the case furthest from the switch end, which took about three weeks. Upon close examination, there was a crack in both corners where the back panel meets the sides of the main body at almost 90 degrees. Verdict - Poor mechanical design of the case.

    As I don't work in The Repair Shop I bodged it with an elastic band and some Sellotape, which does not stretch as much as PVC tape. Scottiebabe might do better with only the one cell trying to push the case apart. I did think of replacing both cells using rechargeable 2/3rds AA's with solder tags, arranged so that the cells have to be disconnected while charging. One of those little jumpers would do, like the ones scattered about on PC mother-boards etc, in series with a solder tag. But then I decided that as these lights would only be used for a few days of the year and that not many visitors would be interested in the contents of the battery box, I'd stick with the Sellotape and the rubber band. 

Comment

  • I bought one of these a few years ago. A simple device, no electronics (apart from the LEDs), just an on/off switch. The lights were quite Christmassy. The main problem was that the springs used for the battery contacts were far too strong. This resulted in the eventual bending-backwards of the end of the case furthest from the switch end, which took about three weeks. Upon close examination, there was a crack in both corners where the back panel meets the sides of the main body at almost 90 degrees. Verdict - Poor mechanical design of the case.

    As I don't work in The Repair Shop I bodged it with an elastic band and some Sellotape, which does not stretch as much as PVC tape. Scottiebabe might do better with only the one cell trying to push the case apart. I did think of replacing both cells using rechargeable 2/3rds AA's with solder tags, arranged so that the cells have to be disconnected while charging. One of those little jumpers would do, like the ones scattered about on PC mother-boards etc, in series with a solder tag. But then I decided that as these lights would only be used for a few days of the year and that not many visitors would be interested in the contents of the battery box, I'd stick with the Sellotape and the rubber band. 

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