Monday, March 25, 2013

SPI, Buttons, Toasters, and More

Just a small update today on what I’ve been working on.
  • nRF51422 – Talking to the ADS1247 on the SPI bus, figuring out the reference code, and reading and writing pins.
  • Looking into Gyro’s. They have very very high current consumption. 4.2 – 6.4ma. This is much to high. I can’t find any stats on start up time. Sleep mode doesn’t reduce current below 2ma. Still too high.
  • Strain Gauges – Not much new, but I’m hoping I can find 1000 ohm gauges instead of 350 ohm. This will save power
  • Toaster Oven – I’ve decided to make a reflow oven. This should speed testing new circuit boards. I have an SSR on order, and a thermocouple and sensor chip on order from Adafruit. Let’s see if I get dinged with Tarrifs.
  • I’m interested in going to the ANT+ Symposium in Sept, but looks like I’ll have to upgrade to Alliance Membership. $1500 dollars a year is a little hard to swallow right now. If I’m in the market for beta testers by June I’ll sign up then and just suck it up.
  • Beta Testers – If you’re a cyclist in Ontario or know someone who might be interested in testing my next prototypes have them drop me a line at either or Oh no, I gave away my new company name! Website coming in a month.
  • I’m thinking about making the board, or a variation of it, available to the hacker community. The plan would be to have space that other sensors (Accelerometer, Gyro, Magnetometer, General Purpose Analog Input with Gain [ADS1247/8]). Idea for now. ANT+ for all I say (but become an Adopter to get the ANT+ Key of course at )
  • Below is some testing. I’m sure all are becoming familiar with my laptop layout.
  • While I might pick up a BTLE sensor Tag from TI, I have no ambition to pursue BTLE at this time. Cost mainly. ANT+ will require FCC + $1500 membership + $750 device registration / testing. BTLE requires $22500. I am not joking. I became a BTLE adopter and I can barely understand the documentation and only have the vaguest ideas how it works compared with ANT+. Right now that’s a learning curve I am not willing to accept. If Accuity gets off the ground, has people test some prototypes, then I’ll reconsider.


  1. ST's L3GD20 has a sleep state that draws 2mA OR a power down mode the draws 2uA.

    Both mention a 'turn-on' time, but give no reference numbers in the datasheet.

    Hugely keen for a hacker board. I would love to make my own power meter I can tinker with and have been following your blog closely.

    1. Sadly 2ma is actually higher than I want and it's 6.1ma while reading. I'm trying a 4ma analog one. I'm undecided on analog versus digital. More to come.

  2. The MPU-6050 might also be a option for a gyroscope, at least during prototyping since it is not only a gyroscope but also an accelerometer. The gyro is still power hungry with a consumption of 4 mA, but when you can turn it off and only use the accelerometer.

    1. This is the option used on the BTLE Sensortag from TI I think. It looks similar to most I've seen, low cost, etc, but again 4ma is "a lot" in terms of coin cell operation and the 120ms turn on time on some of these is a killer. This necessitates that I can sleep the IO but I can't turn it on or off at will.