Table of Contents
Deployable Generic Wireless Controller
The DevKit Solar Controller is a powerful, low cost solution to monitor and control a wide variety of things. It has also been successfully tested with a solar hot water system. This little device has Built-in-Functions for fast deployment, is easily programmable in BASIC, has an LCD display (3 buttons, 3 LEDs), comes with an External Antenna with a range of over 100m, and has a customizable sensor board. It is powered by household current, as well as from Solar Power. The solar power enables the battery to remained charged in case all power is lost.
Figure 1: Wireless Controller
Simplicity and Diversity
The AIRcable http://www.aircable.net/ DevKit is designed with two major points in mind: simplicity, and diversity. Simplicity comes with the deployable, ease of use design. Diversity is inherent within the device’s programmable options that suit individual needs. In other words, thes controller can acommodate both the novice who simply wants to install a solar hot water system in their home, as well as the engineer who wants to build a custom system with specialized sensors.
Programmable Data Sensing
The diversity lies within the ability to program the device utilizing the easily programmable BASIC, for a virtually unlimited range of data sensing applications. Additionally, the Sensor Interface can be customized since the board itself is customizable. With these two features: a modifiable Sensor Interface, and programming ability, there are an almost unlimited number of applications where the DevKit can “sense” the necessary data, retrieve it, display it, and even perform automatic data logging using the AIRcable Server http://www.aircable.net/server-xr.html with pre-installed Linux, and interpret the results.
Customizable Sensor Board
The housing itself is a generic piece that fits over the customizable sensor board. The board iteslf allows for virtually any type of data sensing for a multitude of applications.
Figure 2: Sensor Board
The DevKit is comprised of the following pieces of hardware:
|ADC converter||3 channel, one common ground, 1.8V pull up for each channel.|
|Battery Voltage Converter||Battery voltage to analog input 1 of the AIRcable controller.|
|Flow Sensor||Frequency to voltage converter, reference voltage for the sensor, analog output to analog input 2 of the AIRcable controller. Has a little turbine inside with magnets on the fan blades. The blades turn when water flows through which measures the amount of water passing through the pipe.|
|Heat Exchanger||Does as the name states, exchanges heat, in this case, lowering the initial temperature of the water coming out of the main water tank before it continues on up to the solar tubing on the roof. This will only run if the Water Tank Temperature Sensor indicates that the water is too warm. When the Heat Exchanger is triggered, the heat is transferrred to an external source. In Figure 4, “Flow System,” on page 12, the Heat Exchanger triggers the pool pump to begin flowing water through the system in order to transfer the heat away from the solar cold water pipe.|
|Sensor: Light||Sensing voltage from the solar cell to run the pump as well as to charge the battery in the controller.|
|Sensor: “overheat”||The “overheat” sensor measures the water temperature after it passes through the heat exchanger on the solar cold water line. This is the water temperature that will go up on the roof into the solar panel. If the water is too hot to be allowed into the solar coils on the roof, it will trigger the Heat Exchanger to cool the water temerapture down further and transfer the heat onto another external source such as a pool.|
|Sensor: Solar Water Temperature||Provides a temperature reading of the water after it has been heated through the solar tubing.|
|Sensor: Water Tank Temperature||Provides a temperature reading of the water initially coming out of the water storage tank.|
|switch for pump #1||New MOSFET switch with TTL level gate. This pump works off of full pressure house water supply. Note: Pump runs off of solar energy which means that the pump only runs when the solar panel is converting sunlight to energy.|
|switch for pump #2||(pool: used in this case as an external place for transferring excess heat to) A low power pump using low pressure water from the external water source (the pool). Note: Pump runs only when the Heat Exchanger triggers it to run water in order to transfer heat away from the solar cold water pipe.|
Long Range Wireless Communication
The External Antenna provides a range of over 100m allowing for sensory data retrieval in areas where wired communication may either be unfeasible or impractical.
By using a flow sensor to determine how much water is going through the pipe, and multiple temperature sensors that provide temperature differences, the device is able to display the following bits of data on its LCD screen:
Figure 3: DevKit tied to Solar Panel
||Reads water temperature in the pipes on the roof. Measures in °C.|
||Reads the temperature of the water in the cold water line after the water has run through the Heat Exchanger. If the water is “sensed” to be too hot, the heat exchanger will be prompted to pull more heat away from the water to cool it down further. Measures in °C.|
||Reads the water temperature that flows from the main water storage tank. Measures in °C.|
|Solar Power (BTU)
||Measures the total kW that the solar panels are producing.|
|Flow Sensor (Energy)
||Has a little turbine inside with magnets on the fan blades. The blades turn when water flows through which measures the amount of water passing through the pipe. Measures enegry in Wh (Watt Hours).|
||Does as the name states, exchanges heat, or transfers heat from one place to another. In this case, if the water coming from the main water tank is too warm, the heat exchanger will cool the water by transferring heat to another source external to the flow system. Measures in BTU/Day or Wh (Watt Hours). Note: Shows up only if the solar temperature is less than the tank temperature.|
Flow System Basics
The flow system on its most basis level works in the following manner:
- Water from the storage tank is pumped out into the cold solar pipe.
- The water reaches the solar coils on the roof where the sun heats the water.
- The heated water runs back down into the water storage tank.
- The AIRcable Solar Controller monitors the entire process.
- The Solar Controller is monitored by the PC and accumulates data throughout the day.
Figure 4: Flow System
Utilizing Existing Hot Water Tank
Figure 5: Connection to Existing Water Tank
Web Display Basics
Your PC will display the accumulated data as it communicates with the controller. The data can be displayed showing daily information as well as information that has been stored into the database showing information over a longer period of time.
The following graph shows a single day of activity. Approximately every minute a reading is taken from the sensors within the flow system thereby providing a temperature difference that can be charted throughout the day. Additionally, the Flow Sensor reads the flow of water throughout the day. This combined data produces a chart showing the total Kw hours produced during the day between sunrise and sunset. The graph will resemble the example in Figure 2 showing the maximum energy being produced at the middle of the day when the sun is at its peak.
Figure 6: Energy Production Graph
The next graph details the type of reading taken throughout the day with flow and temperature difference that gives rise to the graph in Figure 2 showing total accumulated watt hours. This is why a reading is taken before and after the water enters the solar coils.
Figure 7: Flow and Temperature Difference Chart
We wire it like this:
+1.8V reference voltage from the AIRcable SMD
resistor 4.7k Ohm (attached curve shows 3 values: 4.7k, 2k and 1k Ohm)
+— connected to the Analog Voltage input
standard 10k NTC
This way we have a pretty good linear approximation of the sensor.
The formula used to calculate Celsius from Voltage is:
C = 105.1 - V * 0.06957
or approximate: C = 105 - ((V * 3) / 43)
This is one of those design decisions to intelligently attach analog sensors (NTC) to the AIRcable dev kit
slave-linkth-monitor example code
run the parser ./parser.py slave-solar-monitor > AIRcable.bas sort the number of lines, report duplicates ./clean.py file content: slave-linkth-monitor #* Example usage, this will generate monitor ambient testing code as MASTER *# #set global $stream="slave" #include "base/AIRcable.bas" #include "shell/AIRcable.bas" #include "monitor/AIRcable.bas" #include "LinkTH/AIRcable.bas"