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Tiara Prototype Assembled

I assembled one of the tiaras in more or less final form last week and while everything is working, and it meets the original criteria, I am working on additional modifications to improve ease of fabrication.  Here is what it looks like at the moment:


The fabrication problems are mostly around the wiring between the PCB and the LEDs.  Soldering to the WS2812s is fussy and the wiring isn't too attractive as seen in this photo from the back:


In addition, I've hot glued a pin header to the PCB and wired to that.  All very unprofessional looking.  There was also a potential problem with shorts when inserting and removing the battery.  So, I've modified the PCB as follows and put them on order:


This will allow soldering in a pin header or in the case of the TSOP 38 direct soldering.  The three LEDs on the old receiver PCB have been replaced by a four pin 5050 SMD version of the WS2812. In addition, I am switching to the same LED for external lights and designed a small PCB to make attachment easier - they are a bit more than 11 mm in diameter:


There was a recent blog on Hackaday about cables and I am thinking about ordering some custom ones to tidy up the wiring:  http://hackaday.com/2017/06/25/dirty-now-does-cables/.  Of course this will require yet another spin of the PCBs to accommodate the new cables but in the end it is all easier to assemble and neater.

Meanwhile, the prototype I built for the transmitter looks crummy and I am still waiting on some parts.  Plus, it was suggested that I needed to simplify the programming by the user further and perhaps have an automatic mode that would somehow work without programming on behalf of the user.  So, I've ordered some MSGEQ7 Band Graphic Equalizer chips with the idea of using that plus volume to create some kind of automatic light show (feature creep alert).  I will probably switch to a Raspberry Pi for the transmitter.

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New IR Transmitter Prototype Assembled

I have not received the new PCBs yet but I did get the IR LEDs so I put together a "boosterpack" transmitter and a separate module to test coverage and range.


They can be used together with crossed beams for coverage from two sides.  The IR LED array on the left is lit, but since it looks to be off, it is apparent that my iPhone has an IR filter on it.  Total current when on is on the order of 400 mA per bank and is controlled by a TIP120 Darlington Transistor which is all I had on hand that could carry the current.  The TIP120 on the left has a heat sink on it but I found that wasn't necessary and the one on the right is bare. The LEDs are capable of 100 mA continuous each but are seeing less than 50 mA at peak here.  If you look closely at the bottom row on the booster pack you can see the 0805 SMD resistors that are in series with each LED.  Power is coming from a 1200 mAh lipo beneath the LaunchPad which seems sufficient for the task.

This thing puts out a lot of photons compared to what I was using before.  Indoors with white walls it even bounces around corners.

I learned the following which will need to be incorporated into the next iteration:

  • The beam is too narrow.  I discovered this by testing outdoors with no walls to bounce off of.  The LEDs I bought were from China and did not have a complete datasheet.  Possible solutions are wider beam LED(s), angling them in such a way as to spread the beam, possibly reflect them with an umbrella as is sometimes done with a photographic flash.
  • Use more SMD components.  I would like to reduce the hand soldering.  Looking for a SMD enhancement MOSFET that can handle 1A at 3.3V and not overheat in a small enclosure plus IR LEDs that fit the spec.
  • Find an off the shelf enclosure and design around it.

The receiver PCBs and WS2812 PCBs should come in next week.

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Once you start down the rabbit hole there is no end of unexpected things :smile:

I believe the ones I have are for TV remotes or something like that where the user aims the controller at the device and tight focus is desirable.  For example, here is the Everlight IR333A - my crude measurements show something similar:


My idea for angling would be to make the PCB something like this for the desired angles and bend the legs of the LED 90 degrees to point them in the right direction:


This would not be a good solution if the goal is SMD and simplified manufacture of course.  Plus, it wouldn't fit neatly into a off the shelf enclosure.

Other LEDs can be purchased that have a wider beam.  For example there is a Kingbright  SMD 0605 LED that is good for 50 mA and has 50% relative radiant intensity out to 120 degrees.  Note that the example about had 50% relative radiant intensity only out to 20 degrees.  I would need a lot more of them but they should be easier to assemble than bending leads and through hole soldering.  It is also possible to get single LEDs rated at 1 Watt which might do the trick.

Another idea to reduce parts is to use resistor arrays instead of individual resistors.

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  • 2 weeks later...

Project Closure

Here are the original objectives along with closure notes that may be of interest to some...

  • cost - unit cost for the receiver of $10 or less - The project came in at less than $10 for each receiver, even in small quantities.
  • technology - common off the shelf components, MSP430G2553 - The G2553 was more than adequate for the project.  Also used the TSOP38238 for infrared and the SK2812 for LEDs which are readily available and inexpensive.
  • construction - standard double sided PCB spec, keep SMD parts large enough to be hand soldered - I used OSH Park for the PCBs and 0805 components for the jelly bean parts.  Everything was hand soldered.  I did find it a bit difficult to hand solder the SK2812 and had to go back and retouch a number of them up.  Not sure why, the part is relatively large.
  • power - CR2032 (rated 3V and 225 mAH) - Worked well, even with the SK2812 which have a higher voltage on the datasheet and despite drawing 10 mA or more.
  • life - needs to run at least half an hour on fresh batteries - Battery life is easily an hour or more the way I am using it.  Current is on the order of 10 mA as noted above.
  • reception - 10m with clear line of sight, update at least every 100 ms - This is easily done provide there is line of sight and IR LEDs with sufficient beam width are chosen.  As noted in the thread above, multiple transmitters can be used which can help meet this requirement.
  • transmission - desirable but not required - I chose not to make the receivers capable of transmission.
  • size - 40mm/1.6" diameter for receiver - Easily done, see photos below.
  • programming - Energia desirable - The receivers were programmed in Energia as noted in the thread above.  The transmitter was programmed with CCS but I ended up using UART to communicate with it.  Accordingly, any computer or microcontroller with UART can be used to direct the transmitter.  This was actually one of the more interesting parts of the project and I may write a tutorial on the method at some point in future.
  • schedule - 6 month completion - It ended up taking 7 1/2 months but could have been done in half the time without my usual side tracks and procrastination.

Here are some shots of the finished parts...


Each receiver has a SK6812 soldered to it - it is lit red in the photo.  The onboard SK6812 is not used in this project, instead a string of SK61812s is soldered on the 0.1 inch pitch header on the right side of the board (Dout, GND, and 3V3).  The IR receiver is soldered to Pin 3, GND, and 3V3.  Other pins, labelled with Energia pin numbers, are also available to the user.  Programming access is at the top and I usually use Pogo pins although a male or female 0.1" pitch header could be soldered in.


The 2032 battery is inserted from the bottom.


On earlier versions I used WS2812 LEDs already soldered to PCBs for the string that is hot glued into the tiaras but ended up making my own and soldering SK2812 LEDs to them for the final project.  The pins are "breadboard friendly".  SK2812s are essentially the same as WS2812s and "Neopixels".


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