GSM/GPRS Modem Board

This week we tested our new Telit GL868-Dual GSM/GPRS board. The GL868-Dual is a dual band 900/1800 MHz GSM/GPRS device.

This board is suitable for providing cloud connectivity to a remote instance of a WiSense wireless mesh network. The board can work directly off a Li-Ion battery which could in turn be charged by a solar panel or even mains AC if available.

This board can be easily interfaced to a Raspberry PI using an USB to serial (RS-232) adapter. The 5V output of the Raspberry PI should be used to power the board’s comm interface (see supply (2) below).

The GL868-Dual board can also be interfaced to an external micro-controller such as the MSP430 on a WSN1120CL coordinator node. The external micro’s supply voltage can be different from the power supply provided to this board. This is possible since this board utilizes voltage translator ICs for all exposed GL868-Dual signals. The external micro’s supply voltage should be used to power the board’s comm interface (see supply (2) below).

The GL868-Dual peak current draw is around 2 Amps.

Interfaces:

  • Power supply (1): 3.8V  to 4.2V  (Allows the board to work directly off a single cell Li-Ion battery) through 4 pin screw less terminal block.
  • Comm interface voltage supply (2) allows board to be interfaced with external micro-controller / R-PI etc through multiple voltage translator ICs. This is independent of the power supply (1) mentioned earlier.
  • Mini-SIM card holder
  • Comm interface:
    • RS-232 (TX/RX) through a  DB-9  connector
    • UART (TX/RX) on 2.54 mm pitch headers.
  • Other exposed GL868-Dual signals (through voltage translator  ICs) on 2.54 mm pitch headers.
    • RESET_M
    • ALARM_M
    • BUZZER_M
    • RFTXMON_M
  • External signal which controls a load switch gating power supply (1) to the GL868-Dual modem.
  • Antenna  connection through u.fl connector.

PCB specs:

  • Layers: 4
  • Dimensions:  69 mm x 82 mm
  • Finish: ENIG
  • Mounting holes: 4
  • All components mounted on top side.

Here is a  pic of the board.

gsm_board_pic

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

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Wireless Soil Moisture Sensor

We got a 3d printed enclosure for our soil moisture sensor thanks to Vikram Rastogi who runs Hacklabs.in  (co-located at Nasscom COE-IOT). This was our first experience with 3d printing and we are happy with the outcome.

The 3d enclosure has two parts. The top part can be screwed on/off the longer bottom part.

The moisture sensor is connected to a WiSense WSN1120L sub-GHz wireless node through 4 wires (2 for power and 2 for the I2C bus).

In the pic below, you can see the soil moisture sensor connected to the WSN1120L mounted inside another weather proof enclosure.

wms_pic_1

Here’s a close-up of the 3d printed enclosure.

wsm_pic_3

Here’s a pic showing  the sensor in action outside Nasscom COE-IOT in Bangalore. The soil moisture data is being  sent (every  5 minutes) to our data collection/visualization application “WiSight” running  on AWS.

wsm_pic_2

Here is a  snapshot of the sensor data from WiSight.

wsms_graph_1

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

Solar + Li-Ion Power Supply Unit

This week we started  testing our brand new solar charger PSU design. The solar PSU powers a WiSense WSN1120L node operating in full function device (FFD) mode. FFDs are involved in mesh  routing and therefore need to keep their radio on at all times.  The WSN1120L’s current consumption in this mode is around 31 mA  in normal receive mode and  around 50 mA  when transmitting at +13 dBm.

The solar PSU also supports continuous measurement of the panel voltage and current as well as the battery voltage and current. This data is being sent every 5 minutes to the  cloud. See the graphs at the end.

The  PSU supports panels with voltage output up to 10.5V. The PSU allows charge current of  up to 2 A which allows high capacity Li-Ion batteries to be charged by high wattage panels.

 

sol_li_ion_charger_pic

Test Panel Specs

  • Peak  power: 3  Watts
  • Voltage output at peak power point: 8.5V
  • Current output at peak power point: 300 mA

Test Battery Specs

  • Chemistry:  Single  cell Lithium-Ion Battery
  • Capacity: 1100  mAh
  • Output voltage: 3.7 V  (nominal), 4.2 V (full charge)

Charger PSU Board Specs

  • Max  input voltage:  10.5 V
  • Max charge current: 2  A
  • Max  battery discharge  current: 4 A
  • Li-Ion battery charged in 3 phases (trickle charge,  pre-charge, constant  current and constant voltage).
  • Battery under-voltage lockout supported as load is not connected directly to battery.
  • Charger IC can power the load and charge the battery simultaneously.
  • Multiple output voltages
    • 3.3V  (Max 1 A)
    • 4.9V (Max 50 mA)
    • Li-Ion battery output (Max 4A). This supply is gated by a load switch which can be controlled by a signal external to the PSU (for example – by an external micro-controller).
  • On board  current and  voltage sensors which measure the following  parameters:
    • Solar  panel output voltage (Available over I2C)
    • Solar  panel output current  (Available over I2C)
    • Battery voltage  (Available over I2C)
    • Battery current  (Available over I2C)
  • PCB specs
    • Layers: 4
    • Dimensions:  53 mm x 48 mm
    • Mounting holes:  4
    • Finish:  ENIG

Here is  a pic of  the  setup. You can  see the 3W  panel lying flat and connected to a weather proof enclosure containing the PSU, battery and an WSN1120L. This location is not the best with tall structures/buildings in the vicinity.

solar_psu_pic_1

Snapshot of battery voltage and current (captured from WiSight running on AWS).

li_ion_batt_charge_graph_1

li_ion_batt_charge_graph_2

For more information on our products, please visit wisense.in.

RS-485 interface for water meters

This week we tested a new RS-485 board to be used for wiring water meters for apartments. This is in addition to the wireless water meter solution we developed last year using the WSN1120L wireless mesh nodes.

In apartment complexes, water meters are usually one below the other in one or more plumbing/utility shafts. Wiring meters using a multi-drop bus such as RS-485 is a  more  cost effective and reliable solution in this case.

In India, it is common for apartment complexes to have multiple water supply entry points for each apartment. This means we need multiple water meters for each apartment. These entry points are usually not close to each other. Multiple RS-485  strings are therefore required to connect all these meters. All this adds to the cost of the overall solution.

We have so far tested 1  master  RS-485 node and 2 slave RS-485 nodes.  Each master node can collect metering data from up to 31 slave nodes.  A slave node can  accommodate two water  meters. The master node will have a wireless interface (WiSense Sub-GHz radio or GSM/GPRS module) for cloud connectivity. Even if there are multiple RS-485  strings, only one master  node needs to have GSM/GPRS connectivity.  All the other master nodes will connect to this one over the WiSense Sub-GHz radio network. Broadband internet connection (if available) can be used  instead of GSM/GPRS.

Here are a  few pictures of our initial test setup. You  can see the master connected to a  slave through 50 feet of shielded twisted pair  CAT-5E cable.

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Here is a closer  look at our RS-485 interface board.  Each board has a micro-controller, an RS-485 transceiver providing half-duplex communication and a 5 bit dip switch for assigning address (1 to 31) with 0 reserved for each string’s master node. All the nodes are daisy  chained. Power is supplied through the master node over the CAT-5E cable.

rs_485_board_pic_2

Here is a pic of  a water meter connected to a slave board.

wwm_pic_1

For more information, please visit wisense.in.

WiSense Wireless Node for Agriculture

We have developed a multi-sensor wireless node for agriculture related monitoring and control applications.

This sensor node is  based on the WiSense  WSN1120L sub GHz wireless mesh node.  This “agri node” operates in the license free 865-867 MHz in India. The nodes have  a max transmit power of  +14  dBm and a range of about 1 KM (LOS) and around 0.5 KM  (non LOS).

The node includes the sensors listed  below:

  • Relative Humidity (CC2D33S)
  • Temperature (CC2D3SS,  LM75B and an NTC thermistor)
  • Ambient  light (TEPT5700)
  • Atmospheric pressure (MS5637)
  • Soil temperature (based on an NTC thermistor)
  • Soil Moisture (Capacitive)

We can add  more sensors based  on customer requirement and energy budget. The selected sensors are relatively low cost.

The node can be  operated as an  FFD (takes part in mesh routing) or as an RFD (no routing). In the RFD configuration, the sleep mode current consumption  is  around 2 microamps which enables the node to run on limited energy sources such as a pair of AA/AAA batteries, small solar panels and low capacity  rechargeable batteries etc.

The WSN1120L,  battery and related electronics is protected against the elements by a weather proof  enclosure  (IP65/ABS).  The humidity, pressure  and temperature sensors are protected by a radiation sensor. These external sensors connect to the  WSN1120L through a weather proof 4 wire cable.  Similarly the soil temperature and soil moisture sensors connect to the WSN1120L through a 2 and 4  wire cable respectively.

In addition, the “agri node” can be used to control valves, motors etc using add on relay boards.

The coordinator node (WSN1120CL) can be interfaced to the available back-haul mechanism such as GSM, 3G, WiFi etc.

We are currently testing a solar  + single cell lithium-ion power supply  unit  which can keep these nodes running  for at least 1 year without any  need to  replace the  battery.

Here is a pic of  a WiSense coordinator node and an “agri node”.

agri_n

 

Here is a pic of  another  “agri node” with an enclosure having a transparent hinged lid. You can see the white colored radiation shield enclosing the three sensors mentioned  above.

agri_n2jpg

 

For more details,  visit wisense.in.

NASSCOM CoE-IOT

WiSense is now part of the NASSCOM CoE-IOT. This a co-working space located on old airport road (Diamond  district) in Bangalore.

The CoE-IOT has lots of very nice equipment and a friendly and engaged support staff. They are always open to ideas on improving the experience for startups.

The equipment includes a top of the line RF spectrum analyzer, an RF vector network analyzer, a signal generator,  oscilloscopes, bench top and hand held multi meters, power supplies etc. In addition they have soldering, rework and inspection equipment.

The  equipment is really useful and  we are now getting our work done much faster. For  example, the PCB inspection scope has helped us identify soldering issues with the tiny Balun IC on our RF board.

You get to meet other startups and people working in IOT and related fields. The center regularly hosts guests from within India and abroad. You get a lot of exposure here.

If  you are in the IOT space and need incubation, talk to CoE-IOT. They are always looking for startups which can benefit from the center.

Web: http://coe-iot.in/

Cheap prop/stand for WiSense nodes

I  have  been  looking for a cheap and easy way  to use WiSense nodes in the lab without having to put each node in an enclosures. I want to be able to quickly attach and remove the debugger on any node. The problem is keeping the bulky half-wave dipole antenna upright. The  antennas need to be propped up properly otherwise it will keep falling. This week I found a way to do it and  it doesn’t look too bad. All I need is a U  clamp and a long screw. Here are  some pics.

jugaad_node_1

 

Here’s  a closer  look at the  sensor  node. You can see a  CC2D33S humidity + temperature sensor sticking out from the node. 

jugaad_node_2

 

 

For more  information on WiSense, visit wisense.in.

WSN1120L / WNS1120CL Block Diagrams

 

wsn1120l_block_diagram

WSN1120L Hardware Block Diagram

 

wsn1120cl_block_diagram

WSN1120CL Hardware Block Diagram

 

Work in progress – New Micro

It’s  been a while  since we upgraded the microcontroller on WiSense nodes. The last upgrade was from the MSP430G2553 to the MSP430G2955.

The MSP430G2955 has 56 KB code memory (on chip flash) , 4 KB of  RAM and max clock speed of 16 MHz. The current  set of features  have  exhausted the code  memory so it is time to move to another member of the MSP430 family. This time we are upgrading to the MSP430F5419A. This is  a 100 pin micro with 128 KB  of  code  memory (again  on chip flash) and 16  KB of RAM. This micro can run at a  max  speed of 25 MHz. It has far  more  GPIO  pins (87 compared to 32 on the G2955). It has 16  12-bit SAR ADC  channels  compared  to 12 10-bit SAR ADC channels  on the  G2955. The  F5419A  has  4 “Universal Serial Communication Interface (USCI) blocks” compared to 2 on the G2955A. Obviously the F5419A costs more. So it is an upgrade on all fronts.

Since we chose to have separate PCBs  for the  micro and the  radio, changing either the radio or the micro is not a big effort.

Reduced  function devices can still use the MSP430G2955 but all FFDs and coordinator nodes will use the  MSP430F5419A going forward.

Board changes will include a 25 MHz crystal for the F5419A  and a  bigger external  EEPROM  to accommodate two 128 KB  images (for  firmware upgrade). Will add a JTAG  interface in addition to the 2 pin SPY-BI-WIRE. Debugging with the full JTAG  interface is far more convenient (and fast) compared to the SPY-BI-WIRE interface. I  have not yet decided on the PCB size and the number of GPIO pins which will be exposed.

The advantage of sticking with the MSP430 family is that all the code base (pretty big now) runs on the F5491A as it is. Peripheral register naming is slightly different between the F5419A  and the G2955. The F5419A has a highly configurable 12 bit ADC so all the device drivers using the simpler  10 bit ADC on the G2955 need to be modified to use  the new  12 bit ADC module.

I  was able to interface the CC1120 radio and  got the UART working on the F5419A. I tested both the FFD and Coordinator configurations. Looks good so far. Was not able to get the clock speed to 25 MHz maybe because I am currently using the MSP-TS430PZ5x100 Target Socket Module instead  of a PCB mounted micro.

Here are some pics of the eval setup.

img_1862

 

img_1863

 

 

For more information, please visit wisense.in.

WSN1120L/WSN1120CL with low profile radio boards

We reduced the size of the radio boards  on our WSN1120L and  WSN1120CL nodes. The earlier version (WSR1120 Rev 1.0) of the radio board had both a U.FL connector and a PCB antenna. The new version (WSR1120 Rev 2.0) only has a U.FL connector. The dimensions of the new radio board are 27.5 mm x  27.5 mm. These radio boards use the CC1120 radio from TI.

 

cc1120_latest_ffd

WSN1120L  with the new radio board (WSR1120 Rev 2.0)

 

 

cc1120_latest_coord

WSN1120CL with the new radio board (WSR1120 Rev 2.0)

 

wsn1120l

WSN1120L  with the earlier version of the radio board (Rev 1.0)

 

For more information, please  visit wisense.in.