Author Archives: rkris

New enclosure for sensor nodes

We are now offering sensor nodes with extruded aluminium enclosure.

Enclosure material is anodized extruded Aluminum

Anodizing is an electrochemical process that converts the metal surface into a durable, corrosion-resistant, anodic oxide finish (anodizing.org).

Extrusion is defined as the process of shaping material, such as aluminum, by forcing it to flow through a shaped opening in a die. Extruded material emerges as an elongated piece with the same profile as the die opening (bonnellaluminum.com).

Pics below show a wireless temperature sensor with an external probe. The extruded aluminium enclosure shown is 94mm x 83mm x 30mm in size. The two end-plates have 4 screws each. We have drilled holes in the end plates for the panel mount U.Fl to SMA RF cable assembly and two LEDs. The opposite end plate has a hole for the sensor cable. This enclosure is not IP rated.

Since the material is a metal, this enclosure is not suitable for applications requiring an internal antenna.

For information on WiSense products, please visit wisense.in

WiSense IoT Dashboard

The WiSense IoT dashboard offers real-time sensor data collection and visualization on the cloud. The dashboard has a powerful relational database storage with fast response time for UI data updates. The UI comes with various visualization options and also supports configurable SMS/Email alarm generation features. 

WiSense builds and maintains this dashboard for our customers. Our customers can use it even when they are not using WiSense hardware.

The dashboard can run in the cloud or locally within customer premises.

The snapshots below show a simple dashboard built for a customer’s factory having five WiSense WXI-RH/T-10 wireless sensor nodes sending relative humidity and temperature data to the cloud.

The customer has a (WiSense provided) login id and password to access this data.

The snapshot below shows the visualization screen which can show both real time and historic data. This particular snapshot is showing temperature (T) and relative humidity (RH) data stream from a WiSense WXI-RH/T-10 wireless sensor node installed in chamber 01.

The snapshot below shows the last received sensor data and associated time stamp from the sensor node in chamber-01. In addition, this screen allows the generation of e-mail/SMS alerts through configuration of sensor data thresholds for each sensor data stream.

I will take the relative humidity (RH) data to illustrate the threshold settings. The snapshot shows the upper threshold set to 80 %, the lower threshold set to 40 % and a hysteresis value of 2.5 %. The corresponding chamber will enter an alarm condition when –

  • RH rises above 80 %
    • Here the chamber enters the alarm condition “RH above upper threshold”
  • RH falls below 40 %
    • Here the chamber enters the alarm condition “RH below lower threshold”

The chamber is not in any alarm condition as long as the RH value is between 40 % and 80 %.

The hysteresis value of 2.5 % prevents unnecessary alerts (e-mail/SMS) from being generated in case the RH value fluctuates around the threshold value. It is up to the customer to choose the appropriate threshold and associated hysteresis value.

The dashboard will send out a e-mail and/or SMS to configured recipients if alert generation is enabled (“yes”) for the corresponding sensor data (see snapshot above) stream. An alert e-mail and/or SMS is sent when an alarm condition is entered as well as when the alarm condition gets cleared.

If customer has not enabled alert generation (“no”) for a particular sensor data stream, no e-mail/SMS will be sent out but this event will be recorded and displayed in the “alarms” history window shown in the snapshot below.

Once an alert (e-mail and/or SMS) is sent out, another alert will not be sent out until the alarm condition gets automatically cleared or a different type of alarm condition is entered. For example, if the RH value increases beyond 80%, the chamber will remain in this alarm condition until the RH drops below (80 – 2.5) = 77.5 %. Similarly, if the RH falls below 40 %, the chamber will remain in this alarm condition until the RH rises above (40 + 2.5) = 42.5 %.

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

For inquiries about our dashboard, please write to us at contact@wisense.in.

RH/T Sensor with 3D Printed Enclosure

WiSense is now offering a “Relative Humidity and Temperature Sensor” (WXI-RH/T-10) for demanding applications.

WXI-RH/T-10 (With internal Antenna)

The sensor itself is located inside a 3D printed enclosure. It is connected by a cable to an IP-65 enclosure containing all the electronics (micro-controller, Radio, Battery etc).

The sensor node can be customized according to customer requirement. Here is a list of customizable components –

Radio

  1. USA – FCC compliant (902 – 928 MHz Ban)
  2. EU – ETSI compliant (868 MHz Band)
  3. India – WPC Compliant (865-867 MHz Band)

Sensor

  1. We can replace standard sensor with customer specified sensor
  2. We can also include more than one sensor of any type. Each sensor node can support multiple sensors.

Antenna

  1. Internal to the enclosure
  2. External (connected to the radio through panel mount U.Fl to SMA cable assembly)

Enclosure

We can change the enclosure based on customer specified material, dimensions and ingress protection rating. The default is an ABS enclosure, 120 mm x 80 mm x 55 mm in size and IP-65 rating.

Specs of the default sensor used in WXI-RH/T-10

  • Temperature Sensor
    • Operating Range: -25°C to +60°C
    • Resolution: 14 bit (0.01°C)
    • Accuracy: ±0.3°C
    • Repeatability: ±0.1°C
    • Drift: < 0.05 °C/yr
  • Humidity Sensor
    • 0 to 100% Relative Humidity ( Non- Condensing)
    • Resolution: 14 bit (0.01%RH)
    • Accuracy: ±2.0%RH
    • Repeatability: ±0.2%RH
    • Drift: < 0.5 %RH/yr (Normal condition)
    • Filter cap to resist condensation.

Here is a snapshot of the WiSense cloud dashboard showing sensor data received from a customer’s factory. The wireless sensor node is inside a steam chamber with relative humidity reaching 99 % and temperature above 40 deg C.

Pic below shows a steaming chamber in which one of the sensor nodes was placed. The sensor nodes are sending data to an external gateway node with WiFi back-haul (WSGWIX-110).

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

SIM868 / SIM868E Board

We are going to offer our own SIM868 daughter board in the coming weeks. We are currently testing some of the boards we have assembled.

The SIM868 is a Quad-Band GSM/GPRS + GPS module. The SIM868E modules has BT LE modem in addition. The two modules are pin compatible.

Fully Assembled SIM868/SIM868E Daughter Board

Details

  • Modem: SIM868 / SIM868E (U2)
  • SIM Holder: Micro SIM card holder (J1)
  • PCB
    • Dimensions: 60 mm x 40 mm
    • PCB Thickness: 1.6 mm
  • Antenna Connectors
    • U.Fl RF connector for GSM/GPRS Radio Antenna (P2)
    • U.Fl RF connector for GPS Antenna (P1)
    • U.Fl RF connector for BT module (P3) – SIM868E only
  • Power Supply
    • VBAT
      1. VBAT on J3 powers the SIM868 (Both the GSM/GPRS and GPS parts)
      2. VBAT should be between 3.4V and 4.4V. Recommended voltage is 4.0V.
      3. VBAT should be able to supply up to 2A.
  • Mounting Options
    • This board has been designed to be used as a daughter board mounted on a base board using castellated mounting holes.
    • Four groups of castellated mounting holes (J2, J3, J5 and J9).
  • External Interface
    • V_HOST
      1. This board can run on a voltage (VBAT) which can be different from the voltage (V_HOST) at which an external host controller/processor (to which this board is interfaced) operates. This requires V_HOST to be supplied to this board through a pin on castellated connector J5.
      2. Voltage translated UART Tx and Rx signals. A voltage translator IC is used which take V_HOST and VDD_EXT as input. VDD_EXT is generated by the SIM868/SIM868E module.
    • PWR_KEY (Power ON/OFF control)
      1. This signal can be used to power on / power off the SIM868/SIM868E module.
      2. When signal is low, module is powered off.
      3. To power cycle the module, bring signal low and then take it high.

References

FCC Regulations for  Intentional Radiators in the 902 – 928 MHz Band

In the US, the Federal Communications Commission (FCC) regulates the use of frequencies for wireless communication. The FCC rules and regulations are codified in Title 47 of the Code of Federal Regulations (CFR). Part 15 of this code applies to radio frequency devices operating at unlicensed frequencies and is often colloquially referred to as FCC Part 15.

In the 902-928 MHz band, are no restrictions to the application or the duty cycle which makes this band very popular for unlicensed short range applications such as general wireless sensing and control whether periodic or even driven.

Wireless nodes operating in the 902 – 928 MHz ISM band are classified as intentional radiators and their emissions are subject to the limits given in FCC section 15.209. The maximum power allowed for unlicensed short range applications is –1.23 dBm (EIRP) or -3.38 dBm (ERP).  This limit is applicable to PHYs such as FSK and GFSK.

Even higher output power can be used if the system employs some form of spread spectrum such as frequency hopping or direct sequence spread spectrum. The reason such allowances are made is that spread spectrum systems are less likely to interfere with other systems than are single frequency transmitters. They also have the advantage in that they are often more immune to interference from other systems. The limitations and qualifications of a spread spectrum transmitter are defined in FCC section 15.247

Frequency Hopping Spread Spectrum

  • ≥ 50 channels: +36 dBm (EIRP)
  • < 50 channels: +30 dBm (EIRP)
  • Requirements
    • The transmitter pseudo-randomly hops between frequencies that are separated from each other by at least the 20-dB bandwidth of the data channel, but not less than 25 kHz. 
    • The 20-dB bandwidth of the hopping channel is not larger than 500 kHz.
    • If the 20-dB bandwidth of the hopping channel is less than 250 kHz, the system must use at least 50 hopping frequencies. The average time of occupancy at any frequency (dwell time) must not be larger than 0.4 seconds within any 20 second period.
    • If the bandwidth of the hopping channel is larger than 250 kHz, the system must use at least 25 hopping frequencies. The average time of occupancy at any frequency must not be larger than 0.4 seconds within any 10 second period.

 

Spread Spectrum using Direct Sequence or Spread Spectrum using High Data Rate Digital Modulation 

  • +36 dBm (EIRP)
  • Requirements
    • The 6 dB bandwidth of the modulated signal is not less than 500 kHz.
    • The peak power spectral density conducted to the antenna must not be greater than +8 dBm within any 3 kHz bandwidth. This corresponds to distributing the +30 dBm output power uniformly over the 500-kHz bandwidth.

As the numbers clearly show, FHSS and DSSS radios are allowed to transmit with much higher power.

 

Spurious emission requirements for intentional radiators in the 902-928 MHz band.

For non spread spectrum radios, the spurious emission limit is -41.2 dBm (EIRP). 

For spread spectrum radios, the emission in any 100-kHz bandwidth outside the 902–928 MHz band must only be at least 20 dB below the emission in the 100-kHz bandwidth within the band that contains the highest power. There is a catch though. For fundamental signals in the 902–928 MHz band, the 3rd , 4th , and 5th harmonics all fall into restricted bands. Section 15.209 puts a more stringent limit of -41.2 dBm (EIRP) on these harmonics leading to some design constraints on the output filtering in these systems.

 

Restricted frequency bands relevant to radiators in the 902-928 MHz Band (Section 15.205)

Harmonic # Harmonic Frequency Range Overlapping Restricted Band Frequency Range
1st Harmonic / Fundamental Freq 902 MHz – 928 MHz None
2nd Harmonic 1.804 – 1.856 GHz None
3rd Harmonic 2.7 – 2.78 GHz 2.6 – 2.90 GHz
4th Harmonic 3.6 – 3.71 GHz 3.6 – 4.40 GHz
5th Harmonic 4.5 – 4.64 GHz 4.5 – 5.15 GHz

References:

 

For queries, write to contact@wisense.in
web: http://www.wisense.in

                                                   

Wireless Sensor for monitoring Insulin Temperature

We are working on a wireless temperature monitor for Insulin. Insulin (like the one in the image below) needs to be stored between 2 and 8 degree Celsius. Insulin can be expensive. A single pack containing 5 NovoRapid insulin cartridges costs around Rs 2600 (about $37) . Insulin gets damaged if it freezes. It also gets damaged if exposed to high temperatures. An in-use cartridge can tolerate up to 30 deg C but it should be consumed within 4 weeks.

Even inside a refrigerator there can be lot of variation in temperature from one spot to another. Whenever the refrigerator door opens, temperature rises because of exposure to warm air from outside and it takes some time for the temperature to return to normal after the door is closed. In some refrigerators, the cyclic variation in temperature around the set point (which may be user settable) may result in temperature falling below zero during some part of the cycle.  For instance, a set point of say 2 degrees may result in temperature falling below zero and then rising above zero periodically.

Our solution is a small form factor, single CR2032 coin battery powered sub-GHz wireless node suitable for continuous temperature monitoring. The sensor sends ambient temperature and battery voltage to gateway node which in turn forwards this data to the cloud over WiFi.  A single gateway can handle up to 128 sensor nodes.

We are offering three variants –

  • With FCC certified radio.
  • With ETSI certified radio.
  • WPC/GOI compliant radio for India.

The images below show the tag without enclosure.

insulin_vertical_smaller

Low profile temp tag_smaller

We did not use a BT-LE (Bluetooth Low Energy) radio because of its limited range. These tags will usually be inside a refrigerator while the gateway may be in some other room (next to a wall socket). Sub-GHz radios operating at a low data rate (1.2 Kb/s) will provide a stable link in this situation where as 2.4 GHz BT-LE radios with data rate of 1 Mb/s will most probably not work.

Transmit Power is +10 dBm.  Receiver sensitivity at 1.2 kbps is -112 dBm.

Our solution provides 24/7 monitoring where as a BT-LE only radio talking to a cell-phone will be useful only when the cell phone is in range of the temperature tag.

WiSense offers a gateway with a sub-GHz radio interfaced to a Photon WiFi module.  Here’s a pic of our gateway. We also offer another version with internal antennas.

 

particle_coord_gw

 

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

Temperature tracking in reefer trucks

We are currently working with a client to add wireless temperature sensing to their fleet of reefer trucks.  WiSense wireless sensor nodes are a perfect fit for such applications.  These nodes have a sleep mode current consumption of less than 2 micro-amps – vital for achieving long battery life.  They operate in the license free 865-867 MHz ISM band which has a longer range and better penetration compared to the 2.4 GHz band. Whats more , the sub-Ghz band is virtually unused in India.

Reefer trucks are a vital component of any cold chain.  These trucks have a refrigerated cargo unit to keep perishable goods such as fruits, vegetables, ice cream etc at the optimal temperature.  I was talking to a group of reefer drivers near a cold storage facility in East Bangalore. This group had just delivered trucks full of Amul ice cream from Gujarat to Bangalore – a non stop journey of forty hours in the blistering heat of  an Indian summer.

Here are some pics courtesy Eicher – a major supplier in India.

The solution required interfacing our coordinator/receiver node  with a GPS/GPRS tracking device. The trucks are currently equipped with a wired temperature sensor. This sensor is installed near the AC inlet at the front of the container. The sensor is wired to the GPS/GPRS tracker inside the truck’s cab. This wiring is also making the solution unreliable,  hence the move to a wireless link.

reef_final

How does the system work ?

We have a high accuracy temperature sensor (with probe) connected to a WiSense WSN1120-P node. This node has an internal PCB antenna and is powered by a couple of AAA batteries.  This sensor node can be installed outside the container with the sensor probe inserted into the container through a hole in the body.  The other option is to install the whole node inside the container.  If the Reefer container is a metal box, it will form a Faraday’s cage which can severely impact RF communication between a sensor node inside the container and the receiver in the truck’s cab. Having said that, reefer containers are not perfect Faraday cages. We placed our sub-GHz transmitter node inside the  container. The coordinator/receiver node in the cab continued to receive packets from the sensor node although we did observe packets being dropped now and then. To avoid any reliability issues, it may be better to install the sensor nodes on the outside of the reefer container.

reefer_500

 

Our coordinator/receiver node is connected to a GPS/GPRS tracker device. We used an analog input on the tracker to forward temperature data received from our sensor node. The receiver node converts the temperature data in to an analog voltage signal using a DAC. This signal is converted in to a digital value by an ADC in the tracker unit and sent to the cloud. The cloud software converts this voltage value back in to temperature.

Here are some pics of the installation.

reefer_100

 

reefer_200

 

reefer_300

 

Here’s a snapshot of the sensor’s data visualized in the cloud.

Temperature Graph

 

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

802.15.4 CSMA/CA

The WiSense MAC is based on the IEEE 802.15.4 standard. It uses the un-slotted CSMA/CA algorithm for transmission of all frames (data and control).

Each time a device wishes to transmit data frames or MAC commands, it waits for a random period. If the channel is found to be idle, following the random back-off, the device transmits its data. If the channel is found to be busy following the random back off, the device waits for another random period before trying to access the channel again. Acknowledgment frames are sent without using a CSMA-CA mechanism.

csma_ca

The algorithm is implemented using units of time called back-off periods, where one back-off period shall be equal to aUnitBackoffPeriod.

In un-slotted CSMA-CA, the back-off periods of one device are not related in time to the back-off periods of any other device in the PAN.

Each device  maintains two variables for each transmission attempt: NB, and BE.

  • NB is the number of times the CSMA-CA algorithm is required to back off while attempting the current transmission; this value shall be initialized to zero before each new transmission attempt
  • BE is the back-off exponent, which is related to how many back-off periods a device shall wait before attempting to assess a channel. BE is initialized to the value of macMinBE.

 

MAC  constants

aUnitBackoffPeriod

  • Description: The number of symbols forming the basic time period used by the CSMA-CA algorithm.
  • Value:  20

 

MAC PIB attributes

macMaxBE    

  • Data Type: Integer
  • Range: 3–8
  • Description: The maximum value of the back-off exponent, BE, in the CSMA-CA algorithm.
  • Default value:  5

 

macMinBE

  • Data Type: Integer
  • Range: 0 – macMaxBE
  • Description: The minimum value of the backoff exponent (BE) in the CSMA-CA algorithm.
  • Default value:  3

 

macMaxCSMABackoffs

  • Data Type: Integer
  • Range: 0 – 5
  • Description: The maximum number of back-offs the CSMA-CA algorithm will attempt before declaring a channel access failure.
  • Default value:  4

 

macMaxFrameRetries

  • Data Type: Integer
  • Range: 0 – 7
  • Description: The maximum number of retries allowed after a transmission failure.
  • Default value:  3

 

CCA

CCA is performed by the radio chip (CC11XX) when requested through the STX command.

  • In IDLE state: Enable TX. Perform calibration first if SETTLING_CFG.FS_AUTOCAL = 1.
  • If in RX state and PKT_CFG2.CCA_MODE != 0: Only go to TX if channel is clear.

If the radio controller is in RX when the STX or SFSTXON command strobes are used, the TX-on-CCA function will be used. If the channel is clear, TX (or FSTXON state) is entered. The PKT_CFG2.CCA_MODE setting controls the conditions for clear channel assessment.

 

Examples

Baud Rate:  20000 symbols/sec, symbol_time is  50 microsecs

Assume macMaxBE is 5 and  macMinBE is 3.

The CSMA/CA procedure starts with BE  = macMinBE

Back_off_duration = (rand((2^3)- 1)) * aUnitBackoffPeriod * symbol_time 

Assume rand(7) returns 7 in which case

Back_off_duration = 7 * 20 * 20 = 2800 micros  = 2.8 milli-secs.

If the  rand(7) returns 0 in which case   “Back_off_duration = 0  microsecs

If BE is set to macMaxBE (5), then

Back_off_duration = (rand((2^5)- 1)) * aUnitBackoffPeriod * symbol_time 

Assume rand(31) returns 31 in which case

Back_off_duration = 31 * 20 * 20 = 12400 micros  = 12.4 milli-secs.

 

If macMaxBE is set to 8 – 

If BE is set to macMaxBE (8), then

Back_off_duration = (rand( (2^8) – 1)) * aUnitBackoffPeriod * symbol_time 

Assume rand(255) returns 255 in which case

Back_off_duration = 255 * 20 * 20 = 102000 micros  = 102 milli-secs.

 

Reference:

Radio power and range – recap

From Wikipedia –

“In electromagnetic and antenna theory, antenna aperture, effective area, or receiving cross section, is a measure of how effective an antenna is at receiving the power of electromagnetic radiation (such as radio waves).

The power received by an antenna (in watts) is equal to the power density of the electromagnetic energy (in watts per square meter), multiplied by its aperture (in square meters). The larger an antenna’s aperture, the more power it can collect from a given electromagnetic field.”

Power density at a distance “d”  from the transmitting antenna (with output power  Pt) is given by

Pd =  Pt / (4* (pi) * d*d)

Where  pi  is 3.1414.  The denominator is the surface area of a sphere of radius “d”.

As the distance increases, the power density reduces as square of “d”.

Assuming receiving antenna has an aperture “Ar” sq-m, then power received is  given by:

Pr = pd * Ar = (Pt * Ar)/ (4* (pi) * d*d)

Let us  assume that the receiver is d0 meters away in line of sight from the transmitter and there are no obstructions in between (completely ideal scenario).  Assume Pt0 is  the  transmitter’s  power output.  Then Pr0 is theoretically given by:

Pr0  =  (Pt0*  Ar)/(4*pi*d0*d0)

Let us  calculate the power required if we  want  to double  the  distance “d”  but  still receive  the  same power Pr0 at the receiver.

Pr1 =  (Pt1 * Ar)/(4*pi*d1*d1)

Here d1 = 2*d0   and Pr1  = Pr0

d0*d0 = (Pt0 *  Ar)/(Pr0 * 4 *  pi)  –      [1]

d1*d1 = (Pt1 *  Ar)/(Pr1 * 4 *  pi)     – or –    4*d0*d0 = (Pt1 *  Ar)/(Pr0 * 4 *  pi)  – [2]

Using [1] and [2]

4  * (Pt0 *  Ar)/(Pr0 * 4 *  pi) =  4*d0*d0 = 4 * (Pt1 *  Ar)/(Pr0 * 4 *  pi)

– or –

Pt0 =  Pt1 / 4

– or –

Pt1 = 4 * Pt0

The transmitter has to increase it’s output power 4 times to reach twice the distance such that the receiver sees the same power as before.

How much is this increase in “dB” ?

10 * log (P1/P0)  = 10 * log (4) ~ 6 dB

So for every 6 dB increase in transmitted power, the range should double (under ideal conditions).

Let us take a real example. Assume transmitter power is 14 dBm and the receiver is around 1000 meters away and receiving the signal at -106 dBm.

The path loss here is 14 – (-106) = 120 dB.

120 = 10*log(F) =>     12 = log(F)   =>    F =  10^12

The received signal is 10^12 times weaker than the transmitted signal.

 

Let us say, we use a bad RF cable to connect the radio PCB to an external omni-directional antenna on the transmitter and the RF cable has a loss of say 1 dB. How much range loss does this translate to ?

Let Pt0 be the power (in watts) out of the transmitter’s antenna  when using an RF cable of say 0 dB (ideal) loss. Let Pt1 (In watts) be the power out of  the transmitter’s antenna when using an RF cable of  1 dB loss.

10 log (Pt1/Pt0)  = -1 dB

Pt1/Pt0  =10^(-0.1)

Pt1 = Pt0 * (.795)    [3]

The output power at the transmitter’s antenna is now 0.795 times the previous  power.

Pr0  =  (Pt0 * Ar)/(4 * pi * d0 * d0)         [4]  When using cable with 0 dB loss

Pr1  =  (Pt1 * Ar)/(4 * pi * d1 * d1)         [5]  When using cable with 1 dB loss

We  are interesting in finding the new distance  “d1” at which Pr1 is same as  Pr0.

Pr1 = Pr0       [6]

From [3], [4], [5] and [6]

(Pt0 *  Ar)/(4 * pi * d0 * d0) = ( 0.795 * Pt0 *  Ar)/(4 * pi * d1 *d1)

We  get,

d1*d1  = 0.795 * d0 * d0    =>     d1 = 0.891 *  d0

The range has reduced by around 11 %.

If power loss is 2 dB,  range loss is 20.5 %.  For 3 dB loss in power, the range loss is 29.2 % and so on.  We think 1 dB loss is not a big deal since we are not used to thinking in dB. As you can see now, small losses here and there (low quality cables and connectors, non optimum RF layout,  mismatched antenna etc) and add up to considerable loss in radio range.

 

 

Solar Li-ion charger board for sensor nodes

We got our first batch of 100 machine assembled solar Li-Ion charger boards useful for powering all kinds of outdoor electronics like wireless sensor nodes and associated sensors/actuators etc.

 

li_ion_c_april_29_18_v1

 

 

Here are the specs for the WLIBPSU v4.0

  • Max  input (solar panel) 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.
  • NTC thermistor as required by charger IC.
  • Multiple output voltages (On separate headers/connectors)
    • ~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 PCB current and voltage sensors (two ICs) which measure the parameters listed below. All values reported over a single I2C bus.
    • Solar panel output voltage
    • Solar panel output current
    • Battery voltage
    • Battery current
      • Positive values reported when battery is getting  charged
      • Negative values reported when battery is getting discharged
  • PCB specs
    • Layers: 4
    • Dimensions:  48.5 mm x 48.5 mm
    • Mounting holes:  4
    • Finish:  HASL
    • All terminals are 2.54 mm pitch

Assembled in Bangalore using genuine components (including passives) from USA.

We have tested this PSU with a 3W solar panel and  2600 mAh Li-Ion battery.

Test Panel Specs

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

Test Battery Specs

  • Chemistry:  Single cell Lithium-Ion Battery
  • Capacity: 2600  mAh
  • Output voltage: 3.7 V  (nominal), 4.2 V (full charge)

 

Here is a pic of a WiSense 866 MHz wireless low power wireless node (WSN1120L) powered by the  WLIBPSU v4.0.

Charger PCB, enclosure and battery are inside the enclosure

solar_psu_pic_1

 

 

Battery Voltage Data

solar_2018_may_graph

In the snapshot above, you can see the Li-Ion battery voltage falling during the evening/night and recovering quickly in the morning. This WSN1120L node is operating in RFD mode in which the node stays in ultra low power sleep mode (< 2 uA consumption) and wakes up periodically (in this case every 10 minutes) to sense and transmit data.

If you want to use this charger in your product, we will provide the driver ( c code) for reading the current and voltage measurements.  Note that the charger IC works in stand alone mode. It does not need any external configuration. The voltage and current measurements are performed by two separate sensor ICs (external to the charger IC).  These sensors can be accessed over I2C. You may choose not to read this data.

If you want to use a solar panel with a different Vpeak, we will change the relevant passives free of cost to suit your panel.

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