Approach Draft - Senior Design
Contents
1. and power the unit There is a built in parasitic capacitor that the sensor pulls power from while the microcontroller is reading the data The DS18B20 has a temperature range of 55 C to 125 C This will satisfy the temperature requirement for the ADIC This sensor will be implemented on the ADCI The ADCI is designed to allow for added sensors in the future The possibility of having more sensors added allows the user to customize the ADCI to their particular needs It would be easy to incorporate a barometric pressure sensor or some accelerometers to add to the collected data This data can also be processed by the microcontroller data logged and wirelessly transmitted just as all the current sensors are capable of Other data collection devices may include an onboard camera A camera that has remote triggering capability could be triggered by the microcontroller to take pictures periodically The pictures cannot be sent through wireless communication or stored in the ADCI s data logging module All pictures are held in the camera s internal memory where the user can access them once the package is on the ground 3 2 3 Data Logging As mentioned above the ADCI requires data logging capability Due to the possibility the cellular module fails to send a message the current sensor data must be stored for the user to access after flight The microcontroller gathers the data from all the sensors including GPS location and has to store it al2. cell phone tower making it readily accessible from the ADCI to the computer via text messaging The connection is billed on the amount of data exchange number of text messages transferred and not on the time spent connected or the distance the module has to cover This makes it plausible for the module to always stay connected and ready to receive send data on demand Shown below in figure 3 3 is the block diagram of the Cell module P1018 GPS RESET PIO19 GPS WAKEUP FIGURE 3 3 Cellular module block diagram 3 Above in figure 3 1 there is a RS 232 block this is where the communication will come from when the cell module is active For a clear picture of where the RS 232 connects on the cell module see figure 3 4 shown below otto F Figure 3 4 Serial Interface plug 3 The RS 232 connects to the computer so that the messages being communicated from the ADCI will get transferred to its correct location The Embedded interface is a 50 pin dual row header that allows the ADCI to access many of the available ports and features of the cell module through a single interface 3 Figure 3 5 shows the connection points Bottom View Pans PaRBLAA STARING RLIaBEIS i Pn Figure 3 5 50 pin dual row header 3 As shown above in figure 3 5 the connector is located on the bottom of the unit To aid the ADCI the interface divides up into two groups General Purpose 1 0 input and output interface and GPS Rec
3. some code added after some testing For instance we may want it to send the data to a different e mail in flight by sending a pre selected message to the module Also for cases where the message was unable to be sent from the ground it may be possible to queue the message to be re sent when in contact range without input from the microprocessor Power ON Stage 0 j Get E mail Input Stage 1 l Check Today s Flight Data Stage 2 Pull Data Into GUI Stage 3 NO YES Check for New NO Data Stage 4 Figure 3 7 GUI State Diagram 3 3 3 GUI The current GUI state machine is shown above in Figure 3 7 On startup the GUI is supplied an e mail address by the user where the data is being sent The GUI then polls the e mail account for any data from the current day s flight and displays it along with a timestamp for each piece of data After the initial start up the GUI will check the e mail account every minute for updated flight information and append it to the information on the screen In the future it may also be possible to display the GPS data on Google Maps to give an idea visually of the balloon s path 3 3 4 Usage Cases Graphical User Interface GUI E Mail Client Figure 3 8 GUI Sunny Day Case Figure 3 8 above shows the sunny day case for the GUI On start up it asks the user for e mail address information to poll for data The user pro
4. work for the ADCI and the decision on which was used was not based on any physical parameters The team leader has worked with the PIC18 and PICAXE system before and is more comfortable with it than the PIC24 The main embedded programmer in the group has worked with both the PIC18 and the PIC24 with mini Bully before so both were quite familiar In the end the PIC18 with PICAXE system was chosen due to the group overall being more comfortable with it 3 2 2 Sensors The ADCI has to be capable of measuring location altitude speed and temperature In order to meet these needs several sensors are required The most important measurement for the ADCI is location Location is measured using a GPS module that is incorporated within the Terminus cellular module The Terminus cellular module was chosen for the ADCI because of its capability to measure GPS data and communicates as explained in section 3 2 3 The next sensor on the ADIC is the temperature sensor There are many types of temperature sensors available The first sensor consider for the ADCI was a liner LM34 The LM34 is a three wire IC sensor in a TO 92 package This sensor is inexpensive and is easy to interface with the microcontroller The LM34 has a temperature range of 45 C to 148 C providing a suitable range for the ADCI 1 After consulting with an experienced professor it was determined the LM34 would not be the most suitable choice for the ADCI Since the LM34 is a linear typ
5. 3 Approach The design constraints technical and practical mentioned in section 2 provide an exclusive focus on the development of the ADCI However an analysis of the design aspect is taken into consideration individually to determine the approach of the ADCI prototype this approach is explained in detail in the following sections 3 1 System Architecture The ADCI integrates different sensors along with a long distance communication system A diagram of the system layout is provided below in Figure 3 1 Cellular Temp Module 4 Sensor Microcontroller Figure 3 1 System layout for the ADCI The microprocessor is the central piece of hardware in the system collecting the information received from the different sensors logging that information and sending it on to the cellular module In the best case the temperature sensor and GPS would be completely separate from the rest of the system allowing for them to both be easily replaced later on The temperature sensor follows this ideal but the current GPS unit for cost purposes is on the same board as the cellular module It is however isolated from the cellular module and if a separate GPS is needed later it can be easily added to the system and the current one can be disabled As stated above the microprocessor will be logging the information gathered from the sensors and storing it in memory stored off the chip This will enable a back up of the information in case any of it
6. e temperature sensor operating it at low temperatures will cause electrical noise over the signal wire This will cause the microcontroller to read erratic voltages into the ADC yielding erroneous data Since the balloon will be reaching altitudes of up to 10 miles the ADCI will encounter very low temperatures causing the LM 34 to give incorrect data The current solution to replace the LM34 is the DS18B20 temp sensor The DS18B20 is a programmable resolution one wire digital thermometer The DS18B20 temp sensor can be read using 12bit resolution where as the LM34 could only be read using 10bit resolution The increased resolution means the sensor is more accurate The DS18B20 does not just change its voltage as a function of temperature it also has a built in buffer and hi and low temperature triggers This enables temperature ranges to be set within the sensor itself to notify of an over or under temperature situation Since the IC has a buffer it contains the received information until the microcontroller accesses it A block diagram of the DS18B20 is shown below in figure 3 2 MEMORY AMD CONTROL LOGIC 64 BIT ROM D AND 1 WIRE PORT TEMPERATURE SENSOR SCRATCHPAD HIGH TEMPERATURE TRIGGER TH LOW TEMPERATURE TRIGGER Ti 8 BIT CRC GENERATOR Figure 3 2 Block diagram of the DS18B20 thermometer 2 Yopa CONFIGURATION REGISTER The thermometer can be used as a one wire sensor meaning that only one wire is needed to read
7. e total number of messages the data storage space required is calculated as shown below using equation 1 1408 yter x 120messages 168008 ytes After determining the number of bytes required for a two hour flight we have narrowed down the total choices of data storage to a few that can meet the needs of the ADCI The easiest and cheapest way to store data from the microcontroller is by using an Electrically Erasable Programmable Read Only Memory IC or EEPROM An EEPROM is an integrated chip that is used for non volatile data storage The microcontroller can read and write data to an EEPROM as need without any problem It provides adequate storage space but it is not a removable device If an EEPROM was used the user would be required to have the ADCI connected to a computer in order to extract the data that is stored on the IC This method is not practical because of the added difficulty for the user to retrieve data Another data storage device is a secure digital card or SD card SD cards are very popular in many electronics that stored data such as digital cameras and cell phones SD cards provide data storage ranging from a few MB ranging to 32GB greatly exceed the 16 8KB required by the ADCI unit A disadvantage of the SD card is cost The SD cards themselves are not expensive but the card slot that is used to read and write to the SD card itself is This would accrue added cost to the ADCI package but would also make it more user friend
8. e will poll the e mail account and take any new messages and display them in an easy to read format 3 3 1 Microprocessor The microprocessor cycles through each of the sensors reading new information off them into buffers In the case of the GPS it chooses the middle value from the buffer and stores it For the other sensors the data will be averaged and this number is stored Every minute the microprocessor takes the current sensor data and sends it on to the cellular module and also saves a record of the sent data in the data logger After sending the data to the cellular module the microprocessor waits to see if the message can be sent if not then it makes a note of this in the data logger before starting to read from the sensors again The state diagram of this process can be seen in Figure 3 6 below Power ON Stage 0 Send Data to Cell NO Send timer gt YES gt Module Stage 5 Read Temp Sensor Stage 1 Rees A Pan ecord Failure Successful NO gt Stage 6 Read GPS YES Stage 2 4 Log Sent Data Stage 7 Read Sensor 2 Stage 3 Log Recorded Data Stage 4 Figure 3 6 Microprocessor State Diagram 3 3 2 Cellular Module As of this moment there is no code of our own in the cellular module There are built in commands to take input and send it as a text message to a phone number or e mail address There may need to be
9. eiver interface This enables the module to be accessed through a single port 3 2 5 Power Supply ADCI uses Lithium Sulfur Dioxide LISO2 Batteries to supply energy Each battery has a voltage of 2 9 V and putting 4 of them in series allow approximately 12 V for the ADCI The LISO2 provide the ADCI with mobility portability and reliability The LISO2 batteries are decided due to the power needed for the ADCI power consumption it uses Lead acid nickel metal hydride and lithium ion are three types of batteries that are cable of producing the voltage for the ADCI Lead acid battery is an inexpensive but heavy battery that could form a memory a memory in a battery is caused by overcharging of the battery which will diminish the battery life overtime 4 With nickel metal hydride battery forming of memory and weight are not an effect but it is expensive Lithium ion battery has less weight and no development of memory and it is said to have a better life span when introduce to cold weather With those effects the LISO2 is chosen for the ADCI 3 3 Software Software for the ADCI consists of C code to control the microprocessor and Python for the cellular module as well as the GUI The microprocessor programming allows it to get raw data from the sensors and convert it into a format usable by the cellular module The cellular module coding is then used to convert the data into a text message which can be sent to any preselected The GUI s cod
10. essor is constantly reading new data off of the attached sensors and occasionally sending the data to the data logger Once every minute the microprocessor creates a data package containing most recent sensor information and sends it onward to the cellular module It then waits for the cellular module to say that the message was sent successfully before storing the package and resuming its reading of the sensors The normal operation can be seen below in figure 3 10 Requests Sensor Data s Sensor Data o 2 Log Data o 7 Requests Sensor Data Sends Sensor Log Data Data Logger Microprocessor Send Data Package y Sent Data Package Successfull Cellular Module Log Data Package Figure 3 10 Microprocessor Sunny Day Case Send Data Package Could Not Send Log Data Package Send Data Package Successfully Sent Data Package Data Logger Microprocessor Cellular Module Log Data Package Request Failed Package Send Failed Package Send Data Package ckage Successfully Sent Data Pa Figure 3 11 Microprocessor Rainy Day Case Above in figure 3 11 the rainy day case for the microprocessor can be seen The data package that is sent to the cellular module returns a failure to send notice In this case the microprocessor must make a note along with the logged data that there was a problem sending the package It then returns to
11. is not properly transmitted There are many different storage devices that can be used and these are discussed further on The information gathered in the microprocessor is buffered and then sent onward to the cellular module at one minute intervals The cellular module is able to interpret these messages and turn them into text messages which can then be sent to either another cellular device or to an e mail address where the information can be gathered by a base station computer If there are any problems with sending the data a message can be relayed back to the microprocessor to have it make a note of the failure to send thus allowing data which failed to transmit to be quickly found on the accompanying data logger 3 2 Hardware 3 2 1 Microprocessor The microprocessor has many tasks in the ADCI It must read on data from the different sensors and create buffers for this data At regular intervals it will store the data it has collected on the attached data logger as well as send the current sensor readings to the cellular module at one minute intervals The microprocessor must also be able to identify when the cellular module has an error sending and ensure that the data is not lost There are many different types of microprocessors but due to previous knowledge only the PIC family was researched for this task specifically the PIC24HJ32 using the mini Bully and the PIC18 using the PICAXE microprocessor system Both of the microprocessors will
12. l someplace The microcontroller has enough non volatile memory to store a few samples of the sensor data but not enough to store all data recorded in a two hour flight In order to retain all measured data a data logger is required To meet the data logging requirements for the ADCI several criteria must be met The most important requirement for the data logger is it has enough storage space to hold all data collected during a two hour flight The second is the type of data logger used must be able to interface with the microcontroller The third requirement is that the data logger be removable from the ADCI This will allow the user to retrieve the data once the ADCI is on the ground without any support from the ADCI unit The final requirement for the data logger is cost Data loggers have a wide range of cost so a reasonably priced data logger that meets all requirements is desirable for the ADCI The first step to finding a data logger is determining the amount of storage capacity required For the ADCI the collected data will be stored once every minute over a two hour period of time adding up to a total number of 120 messages The amount of data accumulated for one flight is found by using equation 1 shown below total bytes needed bytes per message X total number of messsa ges 1 The GPS temperature and other sensor data measured by the microcontroller is estimated to be140 bytes Having the estimated number of bytes per message and th
13. ly Another disadvantage is it is more complicated to read and write to an SD card using the microcontroller Although it is more expensive and more complicated to interface it is worth the tradeoff to have the data stored on a removable more user friendly data storage medium Another data storage possibility is adding a USB port to the ADCI that will allow a jump drive to be inserted to store data Jump drives are inexpensive readily available and widely used for portable data storage The storage capacity of jump drives range into the hundreds of GB providing more than enough storage space for the ADCI application USB breakaway boards are available providing an interface for the microcontroller to read and write to an inserted jump drive This method of data storage will be the most portable and the least complicated within the price range for this project 3 2 4 Communication The cellular module is the chosen device to communicate the data primarily because of its speed to transfer data Also the procedure to set up the link between two peers a computer and the ADCI is not time consuming The connection for the Cell module is made towards the internet to achieve a point to point connection between the two Think of the cellular module as a cell phone whereas a phone number is not needed the connection is done with AT amp T wireless This approach has the advantage of shifting the control of the application through the modem directly on a
14. normal operation until a data package is successfully sent When this occurs and the microprocessor receives confirmation that it was sent successfully a request is sent to the data logger for the failed package from earlier and resends that package onward to the cellular module in an effort to transmit any failed data Reference 1 National Semiconductor Datasheet LM 34 precession Fahrenheit temperature sensor Online Available http pdf1 alldatasheet com datasheet pdf view 8853 NSC LM34 html 2 Dallas Semiconductor Datasheet DS18B20 Programmable Resolution 1 wire digital thermometer Online Available http www rev ed co uk docs ds18b20 pdf 3 Janus Remote Communications Datasheet Terminus GSM864Q Hardware User Manual Online Available http www janus rc com pr GSM864Q user_guide pdf 4 Online Mississippi State University Senior Design Archives Available http www ece msstate edu courses design 2008 pwrsupply home html
15. vides information causing the GUI to poll the e mail account for any e mails from the current day The GUI then displays this information for the user Every minute after that the GUI polls the e mail account for any new messages and updates the information for the user A rainy day case for the GUI occurs if it cannot access the e mail account Ifthe user provides incorrect e mail information the GUI will first try to connect to the e mail server If it cannot connect the first step is to check to ensure there is a connection to the internet If not it will inform the user and ask them to ensure that the computer is connected Otherwise if there is a connection then the GUI will tell the user that something is wrong with connecting to the e mail account and requests new account information After this provided the user gives correct e mail information the GUI will poll the e mail and return to normal operation This case is outlined below in figure 3 9 User Provide Correct E Displays Current Fligh uest E mail Address Infor mail Address Info mation Provide Incorrect E mail Address Info mail Address Info t Data Graphical User Interface GUI Requests Today s E mails Could Not Connect Check Internet Connection Internet Connection Okay E Mail Client Requests Today s E mails Sends Reque Figure 3 9 GUI Rainy Day Case During a sunny day the microproc
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