CELSS – System Control Module Schematic is used for controlling the vacuum pump, LED light, pressure pump, defrosting cycle, DP trigger thermo-electric device, freezer and control air valves. The main purpose for this control module is to have a physical connection to all off the CELSS functional equipment and displays all of the data it receives from other modules. It displays on the LED module on the front panel. Data cycles through all variables starting with the measurement name to the left and the measured number to the right, blinking.
This module connects with a laptop where commands can be sent for updating time and date. The connection is through an RS232. Data is also collected on PID commands, gas measurements and control commands. Below is a list of sections just for the Control Module. At the end of this posting is a list and description of each piece of control equipment used to regulate the CELLSS.
The circuit below is a general purpose CPU PIC processor. This particular processor has two I2C and RS232 communication ports. One Rs232 port is used to send data to a laptop while the other is used to send updated information, commands and statuses to other modules through the RS232 network.
I2C communication is used to talk with the Relative Humidity sensor, SHT11. This is shown the second drawing below.
In this application, I’m using the ICD3 by Microchip. The circuit at the top of the drawing shows the connections. The whole system runs on a 20 Mhz crystal. As seen in the picture above, power running this module comes through the network cable. The refrigerator module supplies power. The entire circuit is built on a 0.1″ spacing perforated bread board. Two screws mount it to the CELSS outer box. A MAX232 chip is used to create the typical RS232 logic levels.
This section contains the display. The display is a 16 segment LED display form 1985. I picked this vintage display because it is cheap and easy to interface with the PIC CPU. There are five LED display chips fastened to a board. The interface is a simple 7 bit ASCII data word where the data word is an ASCII character less than 128. No lower case letters. All uppers. Below is a picture of one segment of the display. The part is made by Siemens, DL1416.
The complete display module is made by Siemens, CDA6-1H16-20. It shows up very well at night, but the daylight illumination is very poor. None-the-less this device is priceless when building the entire system. It goes through all of the possible measured and non measured variables and displays them. You can check if data is getting through by watching the display.
The Control Module contains an RH and temperature sensors. These are used to monitor the outside of the system for ambulant changes. When building and designing this system, the project did not turn into a control module for an internal environment, but a huge insulator and compensation device to react to ambulant conditions. I’m spending more time on counter reacting ambulant conditionsthan than trying to accomplish a climate profile. Below is a picture of the RH and temperature device (SHT11).
Since this is the main Control Module for the system, it needs to contain a chip where the Climate Profile is saved. This chip is a I2C 1 MEG EEPROM. The chip is an identical image of the data collections used out in the field for climate characterizations.
Below is the schematic of the I/O control lines. These lines are connected to opto isolators connecting to replays. The replays are connected to the controlling equipment. It is very simple how it is put together. Since the LED display takes 8 bits for each character that is saved in the display, the same pins are used on an external latch. The only difference is another two pins are used for commanding the latch to operate. Data is presented on the same data lines as the display, but are latched be other pins. One pin for each 8 bit latch. You can see the connections for the EEPROM and for the RH devices. The output of the latches are connected to opto isolators. See the drawing below this one.
The next two sections describe all of the systems actuators and control lines to them. So far, there are 9 control devices that directly influences the CELSS. This part of the system is simple; all control lines go through an opto isolator to prevent noise screwing up the CPU. Downstream, the opto isolators control a SSR (solid State Relay). There is an external power supply (not shown) delivering +12 to +16 volts to an isolated noisy system. All SSRs are connected to 120 VAC which powers the system actuators. Please see drawing below.
All of the control lines are connected back to the previous schematic.
Pictured below is a typical refrigerator compressor vacuum pump. It’s connected to 1/4 non-collapsible plastic tubing. The tubing goes into a solenoid. The tube continues out of the solenoid and into the tank. This is where the air pressure in the tank is controlled. You can see the oil level in the vacuum pump.
This fan is used for chilling the whole tank. There is a 4 to 5 inch air gap between the tank and the outer insulation box. Air is moved out of the freezer section of the refrigerator and passed around the tank. Another pipe is installed inside the CELSS system which returns the warmed air back into the freezer. The freezer contains chunks of metal to help stabilize the air.
Aluminum insulation is surrounded the fan and pipes.
Pictured below is a typical airbrush pressure pump. When running, it compresses air until it hits 70 psi. At that time the pumps stops. It’s connected to 1/4 non-collapsible plastic tubing. The tubing goes into a solenoid. The tube continues out of the solenoid and into the tank. This is where the air pressure in the tank is controlled.
LED lights are used instead of HID or florescent lamps. Since the system is very sensitive to additional heat, the heat generated from lights need to be kept to a minimum. The blue/red LED lights are the correct spectrum for plants to grow. HID lamps make way too much heat. Some heat is generated from the LED lamps. This heat is transferred into the tank. Hence, this is how the temperature is controlled when trying to heat the tank. It does not take much heat to raise the tank temperature.
The vacuum pump and air pump each has a solenoid attached to their outputs. The two remaining ports on each solenoid are connected together in a T coupler. The remaining port on the T coupler is piped into the tank. The function of the soilnoids is to keep the air pressure constant in the tank while a vaccuum pump or air pump is coming up to pressure. The vacuum pump and air pressure pumps are not kept on all the time. Once the pressure is correct in the lines, a solenoid is opened and allowed to control the air.
These two solenoid are located under the CELSS system. Below is an “upward” looking shot under the table.
This control device triggers condensation inside the tank. It is used to control the RH inside the tank. Lowering the whole tank temperature to near the Dew Point of the air is not sufficient to reduce the amount of water in the air. There needs to be an abrupt change in temperature, then the water condenses and falls back onto the ground. Think of this device making dew on the grass and the grass is cooled by a clear sky at night.
The freezer is controlled because it needs to be turned off during defrost cycles. Since the freezer interal compartment is somewhat exposed to outside temperatures and moistures, it collects a lot of ice around the in and out ports for the CELSS. Daily, the freezer needs to go through a defrost cycle to clear ice out of the entrance and exit air ports. A 25 watt electric lamp is placed under the holes while the freezer is turned off. The cycle takes about 20 to 30 minutes.
These lights are used for defrosting ice from the in and out ports of the freezer. See the Freezer description for more information.