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I am going to try and update this weekly in the hope it will give me extra impetus to get it done.  I've done more looking at IR and as is normally the case have found lots out there that I didn't know, including some good stuff on 43oh.  To quickly summarize:

  • The IR receiver I am using (TSOP38238) works on 2.5V - 5.5V, and has a typical supply current of 0.27  - 0.45 mA. - seems like it will work OK with coin cell for this application
  • Using a matched 950 nm IR LED with the receiver at the moment.  Even with a single LED transmitter can get 10 m although not 100% reliable.  I expect to overcome this with a more powerful transmitter (e.g. IR illuminator as suggested by chicken)
  • The receiver is sensitive to transmission frequency but that is easily configured in software
  • The receiver is sensitive to burst length but that is also configured in software
  • The receiver is sensitive to spectral wavelength - need to consider this when ordering an IR illuminator ring or constructing a multi-LED transmitter
  • It has vertical and horizontal directivity but this isn't expected to be a problem

Rather than use existing code or libraries I decided to strike out on my own as an educational exercise since it appears to be within my capability.  I started by writing a simple output function at 38 kHz that looks pretty good coming out of the G2553:

post-45284-0-04439500-1482127934_thumb.jpg

Here it is on the oscilloscope after being processed by the TSOP38238 IR Receiver:

post-45284-0-99296700-1482128019_thumb.jpg

Next I made up a protocol for sending 1s and 0s:

post-45284-0-86868300-1482128084_thumb.jpg

OK, should be able to work with that.  Up to this point I had been working in Energia (one of my original objectives) but timing was too coarse in the micro second range.  So I have switched to CCS with the objective of using TimerA0 with interrupts, and then accessing it within Energia.  Tone() won't be usable, but hopefully there won't be other interference inside Energia and I don't need tone().

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I should have labelled this MSP430 Wireless Wearable instead of Wearable with Radio.  Anyway, I have been happy with the progress using IR and plan to commit to it for now.  Here are the options that I considered and the reason for choosing IR:

 

CC26xx - ruled out due to cost - did not pursue technical viability

ESP8266 - ruled out due to power requirements when using CR2032 coin cell - not viable technically

nRF24L - this is a potential alternate, the main concerns are power and distance which I did not pursue to the end.

IR - cost is low, power requirements are low for receiver, able to cram it all into memory and fast enough on the MSP430G2553 if I use CCS and direct register access with C.  The main concerns are distance which should be able to overcome with higher power transmitters  (possibly multiple transmitters) since they need not be powered by a coin cell, and the difficulty in acknowledging successful receipt of a packet.

 

I have started a new thread to document the development of the IR option: http://forum.43oh.com/topic/10098-msp430-infrared-controlled-wearable/

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