From the Lab ...

... Hacking and Slashing since 2002

Since I published the Nordic Smart Beacon, I thought I'd show off what we've been playing with for the past 9 months or so. We've used this same design to do various types of demo sensors. The unit pictured is of a Sensiron SHT21 humidity sensor interfaced to the nRF51822. 
 
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Purchased these a few weeks ago, and have been toying with them. Nice. 
 
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Finally found a nice, gently used, RF current probe. FCC makes some of the best kit out there, and I'm happy to have found this unit for a very reasonable price. Covers DC to 1GHz. 
 
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We've been doing a lot of hacking around with BLE lately, so I thought I'd start publishing some of it. Sorry in advance about the scarcity of details. 
 
Recently we took apart a Belkin Conserve Insight energy monitor (model # F7C005) and determined that the unit used a simple SPI interface to an Analog Device's ADE7753 Metering IC. After sniffing the SPI comms of the original unit, it was pretty easy to tweak some BLE code we had lying around, and get it working with a Nordic EVK. The only real trick was interfacing the power ... the small (ugly) board in the upper right is a small 5V to 3V LDO, which is used to power the EVK. NOTE that we can not (nor should you try) to interface this set up to a computer for debugging. The 5V power supply in the main housing is non-isolated! 
 
The comparative wattage results from our setup to another F7C005 and a Kill-A-Watt were within 1 - 2W over a 1KW range. 
 
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Image of the cable termination (SPI+Power) on the PCB. 
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Pinout. 
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The unit does a little level shifting (the ADE7753 is a 5V part, and the uC in the display unit is 3V). 
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We finally fixed a nagging power consumption issue related to the TWI (nee I2C) on early rev Si of the nRF51822. You can see the PAN for all of the gory details. Suffice it to say, the TWI wasn't shutting down correctly, leaving us with an unexpected +1mA current draw. We poured over some code that Nordic uses in the nRF Smart Remote 2, and adapted it for our needs. Problem solved. 
 
We'll post some "TWI to XXX sensor" examples shortly (IR Temp, Barometric pressure, Humidity, Ambient Temp, etc). 

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