OpenBeacon Sensor

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OpenBeacon Sensor Tag with a 10K potentiometer and constant ADC converting the resistance every 132ms (2.4GHz transmit every 13 seconds and upon change) runs 6 years from a single CR2032 coin cell.
Actual setup when measuring a resistive divider button set - running from a CR123 battery
resistive divider textile button set - each button press corresponds to a certain resistance
Hardware modification for a pressure sensitive wireless touch sensor based on OpenBeacon Proximity Tag to detect high resistances - see picture below for the sensor layout
Special version utilizing the On-Board Darlington transistor circuit to detect resistances in the range of >10MOhm. This allows to detect the pressure intensity on the touch sensor in this picture.

Programming Work Flow

If you want to avoid compiling the latest sensor tag sources, you can find a precompiled sensor firmware here - a script is contained in the ZIP-archive to assign encryption keys and to increment tag IDs by creating patched versions of the contained firmware hex file.

OpenBeacon Sensor Tag related firmware source may be found on our server for occasional browsing and for development purposes in our git repository: 

 git clone http://www.openbeacon.org/openbeacon.git

Please refer to our compiler setup instuctions. Alternatively to git the latest source code snapshots can be downloaded here:

Active 2.45Ghz Sensor Tag Hardware Design

The active 2.45GHz RFID Sensor Tag source code can be found at /firmware/pic16/tag-sensor. You can find further instructions on using our GIT source code repository here.

Basic Sensor Tag Hardware Overview

The OpenBeacon Tag design consists of

  • nRF24L01 2.4GHz transceiver (1/2MBps)
  • PIC16F688 PIC14 microcontroller
  • powered by CR2032 coin cell (220mAh) for up to 6 years of operation
  • resistance scanned 7.5 times per second
  • every 14 seconds or on every resistance change a packet containing the current ADC value is transmitted using the 2.4GHz OpenBeacon protocol. The currently unused field reserved of the protocol RFBPROTO_BEACONTRACKER is used.

Hardware modification for resistive wireless sensor

See picture on the right for actual setup.

  • attach 90° 0.1" 6 pin header
  • connect 3 pin potentiometer (10K) to P1 pin header pin 3 to 5 (3 [V-], 4 Center, 5 [V+])
  • remove R4
  • remove U6
  • replace R5 with zero-Ohm resistor or bridge U6-1 and U6-2 pads with a solder blob after removing U6.

Hardware modification for pressure sensitive wireless touch sensor

See picture on the right for actual setup.

  • attach 90° 0.1" 6 pin header
  • resistive sensor inpit is connected to VBAT
  • resistive sensor output is connected to P2 (before R6)
  • to extend the touch-range, R7 needs to be increased to 22K
  • the darlington circuit (Q1/Q2) needs to be connected to ADC input (RA0/AN0) on P1 (pin 4)
  • remove U6
  • replace R5 with zero-Ohm resistor or bridge U6-1 and U6-2 pads with a solder blob after removing U6.
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