Monthly Archives: August 2016

WSN1120L current consumption

The current consumed by a WiSense  LPWMN  wireless sensor node in sleep mode determines how long the power source will last if the node is configured to operate in RFD (reduced function device) mode and is running on limited energy supply such as a pair  of  AA/AAA batteries.

The WSN1120L  has a bunch of  ICs  (micro, radio and two serial EEPROMS).  When the WiSense  stack puts the node into sleep mode, all of these ICs are put into their  respective sleep modes (usually the mode  with the lowest power consumption). The node’s total sleep mode current is the sum of the sleep mode currents of all these chips.

The pic  below shows the total current (2.2  uA) consumed by a WSN1120L node in sleep mode.

cc1120_rfd_i_1

 

The pic  below shows the current (0.1  uA) consumed just by the radio (in sleep mode) on a WSN1120L node. This matches the number (0.12  uA) given in the CC1120’s datasheet. The  CC1120 retains all of the important configurable registers  in sleep mode so no need to reprogram these registers after waking up the CC1120.

cc1120_rfd_i_2

 

More more information, please  visit http://www.wisense.in.

 

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Hardware Update: New Multi-Sensor Board

We assembled and tested our latest sensor board which supports 7 different sensors.

The different sensors on the board  are:

  • TEPT5700: Ambient light Sensor (Analog)
  • NXFT15XH103:  Thermistor (Analog)
  • LM75B: Temperature Sensor (I2C)
  • CC2D33S: Relative Humidity and Temperature (I2C)
  • MS5637: Barometer/Altimeter (I2C)
  • LIS2DH12:  Accelerometer (I2C)
  • TSL45315CL:  Ambient Light  Sensor (I2C)

In addition there is a buffer IC (SN74LVC1G125DBVR) for interfacing with flow meters with pulse output.

The pics below show the sensor board mated to a WSN1101L wireless mesh node through two 2×7  connectors.

We have  written drivers for each sensor on this  board. All the digital sensors are accessed over a single  I2C bus. We  made sure there is no address conflict. Each sensor responds to a unique 7 bit address.

Each of these digital sensors has a sleep mode to conserve battery life. The analog sensors  are connected to different 10 bit ADC channels on the WSN1101’s  MSP430 micro-controller. Power to each analog  sensor is  gated by a MOSFET which can be  switched off to cut off power to the corresponding sensor and  associated  signal conditioning circuit. Each MOSFET is controlled by a separate GPIO on the WSN1101’s  MSP430 micro-controller.

The  thermistor and the analog  ambient light sensor can be  mounted outside a weather proof enclosure while the rest of the node and battery etc can stay inside.  These  two sensors are connected  to the sensor PCB  through two terminal blocks.

A  U.FL to SMA  RF cable assembly is  used to connect the  WSN1101L’s radio board  to an external bulk-head mounted  antenna.

sns_v3_snsr_brd_pic_1

 

 

sns_v3_snsr_brd_pic_2

 

sns_v3_snsr_brd_pic_3

 

 

For more information, please  visit http://www.wisense.in.

New Sensor Update – Ambient Light Sensor

We recently evaluated an ambient light sensor (TEPT5700) which can be used outside an enclosure. Our requirement is to keep the sensor outside  while the rest of the electronics  stays inside a  weather  proof  enclosure. This allows us to use the light sensor in the outdoors. The other option is to use a PCB mounted light sensor inside an enclosure with a transparent lid.

We chose a through hole photo-transistor which is sensitive to visible light (just like the human eye).  The  current through a photo-transitor  is  directly proportional to the intensity of  light falling on it.

tept5700_ckt

We used used  an op-amp in negative feedback amplifier configuration to amplify the voltage across a current limiting resistor (between the photo-transistor’s  emitter and ground). To increase the supported range (of light intensity) we used an analog switch to change the  gain of the op-amp between two  values  (low gain (2) and high gain (102)). The amplified output (of the  op-amp) was hooked up to a 10 bit ADC channel on the WSN1101L wireless mesh node. The software driver (for this sensor) gets  the ADC output for  both gain values but selects one for  calculating the photo-transistor current depending  on the two values. If the photo-transistor current is low (low light conditions), the ADC output (measured) in the high gain configuration gets  used.  If the photo-transistor current is high (bright light) causing the op-amp output to get clamped at the positive rail in the high gain configuration, the ADC output (measured) in the low gain configuration gets  used.

Here  is a pic of the circuit built on a WiSense  proto board (PB-200).

th_als_eval

 

References:

 

For more information, please visit http://www.wisense.in

WSN1120L Range Test

We did a quick range test of our new CC1120 radio based sensor nodes. We did this within Pruksa (community in east Bangalore).  This  was a non line of sight test in which one WSN1120L node was  configured to send packets to a  coordinator node (a WSN1120CL) once every second. The nodes  were around 526 meters apart with lots of houses in  between.  The nodes were at a height of  around 5  feet above ground. The walls in these houses are fully concrete  (no bricks). Even at this distance the signal strength was pretty good (around  -75  dBm). The nodes were  configured  to  transmit at +14 dBm at a data rate of 1.2  kbps (GFSK modulation) with channel bandwidth configured to 25  kHz.

non_los_test

Map showing location of non-LOS range test

We tried to do a line  of sight test along a nearby highway but we could not find a  flat  stretch longer than 1.1 kilometers close by. The two nodes  were able to communicate up to a distance of 1.1 kilometers. The signal strength  was  again very good (around -80 dBm). We will be doing further  tests to find out the max range  under line of  sight and non line  of  sight conditions.

Here  is a  pic of one of the nodes used in the range test. The node was powered by two AA batteries.

wsn1120l_rt_pic

WSN1120L Sensor Node 

 

For more information, please visit wisense.in.

 

 

Hardware Update – New Radio Board

We  are currently evaluating the CC1120 Sub-Ghz radio from TI.  Our existing solutions use the CC1101 Sub-Ghz  radio (again from TI).

Here is a pic of the first version of  our WSN1120l  mesh node. The radio board is mated to our micro PCB which hosts the MSP430G2955  ultra-low power 16 bit micro from TI. Our modular design allows us to easily change the radio and micro-controller.

wsn1120l

The CC1120 radio board (WSR1120) has a PCB  antenna as well as a U.FL connector to connect to an external antenna.  We will be offering two different CC1120 radio boards (one with a PCB antenna and the other with U.FL connector). The U.FL version will have a smaller form factor (similar to our CC1101 radio board which is 30 mm x 27.5 mm).

This node will also operate in the 865-867 MHz  license free band  in India.

The CC1120 radio control and user interface are based on the widely used CC1101 transceiver.  This relationship enables an easy transition between the two platforms. The command strobes  and the main radio states are the same for the two platforms.

 

Here  are some of the  key differences between the CC1101 radio and the  CC1120 radio. Will include selectivity/blocking in another post. The table shows that the CC1120 is  better in every respect except that it costs more.

Parameter CC1101 CC1120
Data FIFO RX-64 / TX-64    RX-128  / TX-128 
Data Rate    0.6 to 600 kbps 0 to 200 kbps
Sensitivity           –112 dBm @ 1.2 kBaud

  • 865-867 MHz
  • 58 kHz CHF
  • GFSK
  • 5.2 kHz deviation
-123 dBm @ 1.2 kbaud

  • 865-867 MHz
  • 10 kHz CHF
  • GFSK
  • 4 kHz deviation
Max Tx Power +10 dBm +14 dBm   
Operating supply Voltage 1.8V to 3.6V 2.0V to 3.6V
IO GPIO0, GPIO2 GPIO0, GPIO2, GPIO3
External Crystal Oscillator 26 MHz 32 MHz
Digital channel filter programmable BW (CHF)   58 KHz to 812 KHz 8 KHz to 200 KHz 
Narrow-Band            No Narrow-band Wireless Systems With Channel Spacing Down to 12.5 kHz
RF carrier phase noise (indicates quality of carrier signal) -92 dBc//HZ  at 40kHz offset -111 dBc/HZ  at 10kHz offset

(Much better)

Support for re-transmissions No Yes
Support for auto acknowledgments       No Yes
TCXO Support and Control

(Temperature compensated  crystal oscillator)

No Yes
Wave-Match No Yes

 

References:

 

For more information on WiSense, please visit wisense.in.

 

New Prototyping Board – PB200

 

We modified our proto board slightly before ordering another batch. The supply and ground lines are now on both ends.  The PCB material is 1.6 mm thick FR-4 with 1 oz (35 um) copper thickness. The finish is  ENIG. The proto board  is  42  mm by 42  mm with 4  mounting holes. Our WSN1101L PCB is also 42  mm x  42 mm with 4 mounting holes.

PTH (plated through hole) pitch is the standard 2.54  mm (.1  inches) found in breadboards.

These are inspired by the Adafruit perma-proto boards. Very useful when interfacing our sensor node (WSN1101L) to sensors etc.

pb200_front_1

PB200 – Front Side

 

 

pb200_back.jpg

PB200 – Back Side

 

 

pb200_with_wsn1101l

PB200 attached to a WSN1101L

 

For more information please visit wisense.in

Another day, Another Sensor

This time, We interfaced a rain detection sensor to a WiSense WSN1101L wireless mesh node. This is another component in our smart community test bed at Pruksa (East Bangalore).

We are  using  the RG-11 rain sensor from Hyderon. It has multiple modes  of operation. In the “rain detection” mode, the RG-11 output turns on when a given rate of rainfall is detected, and turns off after it has dropped below a threshold. The output remains on for between about 30 seconds and 5 minutes after the last detected rain drop, depending on sensitivity setting and actual conditions.

The RG-11 output voltage goes high (to supply voltage) when the  sensor  turns on. We have interfaced this output signal to a GPIO  pin on the WSN1101L’s micro (MSP430G2955) through a voltage divider  + op-amp circuit. The op-amp output goes high when rain is detected and remains low otherwise.

The  rain detector  sensor node has a simple output – 1 if it is raining, 0 otherwise. This information is being sent continuously to WiSight (our cloud platform running on  AWS).

The RG-11  requires a  minimum of 12  Volts to operate. We get this supply from a  wall wart. This supply is also converted  to 3.3  V to run the WSN1101L .  As you can  see in the pic  below, the  WSN1101L and associated electronics  is enclosed  in a  weather proof  enclosure. The antenna is  mounted outside.

rg_11_inst

 

One use case is to send an SMS  alert to residents who want to be informed when it just starts to rain. Smart watering (of private and public green spaces) can use this  information to decide whether to water on a particular day or not.

 

rg-11_wisight

Snapshot of WiSight (running on AWS) showing data from the RG-11 sensor node.

 

 

References:

RG-11 user guide:  http://hydreon.com/wp-content/uploads/sites/3/2015/documents/rg-11_instructions.pdf

 

For more information please visit wisense.in