Monthly Archives: February 2017
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.
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.
Snapshot of battery voltage and current (captured from WiSight running on AWS).
For more information on our products, please visit wisense.in.
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.
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.
Here is a pic of a water meter connected to a slave board.
For more information, please visit wisense.in.
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”.
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.
For more details, visit wisense.in.