Monthly Archives: August 2016
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.
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.
More more information, please visit http://www.wisense.in.
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.
For more information, please visit http://www.wisense.in.
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.
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).
For more information, please visit http://www.wisense.in
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.
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.
For more information, please visit wisense.in.
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.
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.
|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
||-123 dBm @ 1.2 kbaud
|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
|Support for re-transmissions||No||Yes|
|Support for auto acknowledgments||No||Yes|
|TCXO Support and Control
(Temperature compensated crystal oscillator)
For more information on WiSense, please visit wisense.in.
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.
For more information please visit wisense.in
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.
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 user guide: http://hydreon.com/wp-content/uploads/sites/3/2015/documents/rg-11_instructions.pdf
For more information please visit wisense.in