Class Participation Input Device - Project 38 Report | ECE 445, Study Guides, Projects, Research of Electrical and Electronics Engineering

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CLASS PARTICIPATION INPUT DEVICE

By Ching Man Hui Debi Misra ECE 445, SENIOR DESIGN PROJECT SPRING 2006 TA: Hyesun Park May 1st, 2006 Project No. 38

ABSTRACT

Our project aims to improve the current wireless class participation input device by expanding on the feedback features. The two main components are the Input Device, used by students to input their answers, and the Receiving Device, used by the professor to receive and record the answers into a file. Our main goal is to create a more user-friendly device by implementing an LCD to allow students to ensure that their input device is on the correct channel, as well as to confirm their answers before submission. The improved version will also implement 2 LEDs, one to signal that the data has been transmitted and one to signal that the data has been received. Overall our project was successful, although there are still improvements to be made such as incorporating a “power save” feature. Other future improvements are discussed in the conclusion. Also, our final cost of implementation was higher than expected. We can reduce the costs by using less expensive transmitters/receivers, as discussed in the Cost Section. ii

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iv

1. INTRODUCTION

Several professors at the University of Illinois, Urbana-Champaign (UIUC) have recently begun to enforce student attendance and participation by implementing a wireless input device system in their classes. When a professor asks a question, the students choose an answer using their wireless input devices, and the students’ answers are to be recorded onto the professor’s computer in a data file. If a student answers a question correctly, he or she receives a point for participation. In a particular course held at UIUC, an input device by Turning Technologies, called Response Card RF, is used. Information about this device can be found on the Turning Technologies website.^1 The keypad contains 12 buttons labeled digits 0-9 (A-J), “Go” and “?”. There is also only one LED on the input device to signal successful transmission. What inspired us to improve the class participation input device was the tremendous confusion during the first few lectures of the semester. Due to the lack of a display on the input device, students were not able to confirm that their input device worked properly, was on the correct channel, and sent the desired answer. Students were also unable to confirm that their answer was received and recorded. 1.1 Purpose Our project aims to improve the current class participation input device by creating a more user-friendly version. We believe that the improved input device will benefit students and ease their anxiousness in submitting answers. It will also benefit professors by not wasting valuable class time to set up the system. The improved class participation input device should allow each student to change the channel of his or her input device to use in different classes, ensure that the input device is on the designated channel, confirm answer before submitting, and verify that an answer has been sent and received. 1.2 Specifications The features of our improved input device include: a 16 button keypad, an LCD, and two LEDs. Each input device also contains a transmitter to send answers to the professors’ computers, as well as a receiver for feedback purposes. Our improved input device should meet the following performance requirements:  Illumination of LEDs to confirm data transmission  Less than 2 seconds response time for LEDs to illuminate  200 ft transmitting range The input device will be simulated in a classroom environment. The student will use the input device to submit their answers, and the professor will use the computer to record students’ answers. Improving feedback is one of our main goals, and the LEDs will signal successful data transmission to the students. The response time should be less than 2 seconds to minimize confusion and anxiousness of students. A typical classroom would be no longer than 200ft, thus the input device should meet the 200ft transmitting range.

PIC

The PIC sends the answer to the MAX232 chip, then through the RS232 cable to the computer. With the use of the program HyperTerminal, the professor can choose when to begin and when to stop accepting answers. After the answer has been sent to the computer, the PIC sends a “high” signal to the transmitter to acknowledge successful transmission. Transmitter The transmitter sends a signal to the receiver of the Input Device to confirm that the answer has been received. MAX The MAX 232 chip changes the voltage level from the PIC desired level (5 volts) to the RS desired level (12 volts).

2. DESIGN PROCEDURE

2.1 PIC as Processor for Input Device For the Input Device Processor, we chose to use the PIC16F877A microcontroller because it is easy to use and it is readily compatible with the lab equipment. Also, it is recommended by the Teaching Assistants. The PIC16F877A also has RS232 pins ready for RF communication and numerous I/O pins.^2 The RS232 pins were helpful in outputting the answer to the transmitter, and we used many of the I/O pins to receive input from the number pad, as well as to output data to the LCD and to send a “high” signal to the Red LED as necessary. Unfortunately, neither of us had much experience in code, thus, we chose to program the PIC in C to make use of the given example programs. We were also able to use PIC-C Compiler Reference Manual 3 to understand the built-in-functions. 2.2 Number Pad We used the number pad as provided by the Part Shop. The number pad is a four by four grid with (1, 2, 3, A) in the first row, (4, 5, 6, B) in the second row, (7, 8, 9, C) in the third row, and (*, 0, #, D) in the last row. According to the data sheet, when a button is pressed, two of the eight pins will be connected. So for example, if any of pins1-4 is high while a button on the number pad is pressed, one of pins 5- will be high depending on which button has been pressed. Table C.1 shows which pins are connected when a particular button is pressed. 2.3 Transmitter & Receiver Design The transmitters and receivers, with output from the PICs, are responsible for the RF communication. We chose to use the LINX TXM-900-HP3 transmitter^4 and the LINX RXM-900-HP3 receiver^5 mainly because they were readily available in lab and the range is 1000ft, which more than satisfied our performance requirements of 200ft. Also, both chips provide the capability to choose one of many channels to communicate across, which is crucial to our project because students can change the channels of their Input Device. Furthermore, the power supply necessary for both the transmitters and the receivers was 2.8 V – 13 V, which easily allowed for use of our intended 5 V battery supply. 2.4 PIC as Processor for Receiving Device After much debate, we decided to use a PIC on the Receiving Device to register received data and to transmit the data through the RS232 cable onto the computer. Again, we chose to use the PIC16F877A microcontroller because it is easy to use and it is readily compatible with the lab equipment. Also, it is recommended by the Teaching Assistants. The PIC16F877A also has RS232 pins ready for RF communication. The RS232 pins were helpful in receiving data from the receiver and outputting the answer to the RS232 cable. We were also able to use PIC-C Compiler Reference Manual to understand the built-in-functions. This PIC is also responsible for sending a “high” signal to the transmitter to confirm that the answer has been received.

3.4 PIC as Processor for Receiving Device The design for the PIC on the receiving device is very simple. It simply takes input from the receiver, and sends it to the MAX chip. It also sends a high to the transmitter on the Input Device to indicate that the signal was received.

4. DESIGN VERIFICATION

Our main test was not one involving quantitative data. We want the Input Device to be able to identify input and the Receiving Device to identify user and to record the input. 4.1 Testing Before testing how well all the modules work together, it was important to ensure that all of our modules were independently operating to our satisfaction. How we tested each module is described in the respective locations below. 4.1.1 Number Pad Our results verified that every button on our number pad functions correctly. For example, Figure C. shows the output of pin5 when button 1 is pressed and when we send ‘high’ to pin 1. 4.1.2 LCD The LCD required a series of instructions to initialize. Unfortunately, we had to test both the initialization steps and the write procedure at the same time to receive feedback. We followed the instructions as given in the datasheet, and hardwired the 8 ASCII bits for a “1” to display. We eventually received positive results. Later, we relied heavily on programming the PIC to display students’ choices for answers and channels. We tested each function with the use of LEDs to ensure that every part of the code is reached as desired. 4.1.3 LEDs We tested that the LEDs properly illuminate when voltage is high. We also tested the Red LED to ensure that it illuminates after an answer has been confirmed and ready to be sent, and we tested the Green LED to ensure that it illuminates after the answer has been received by the Receiving Device. 4.1.4 Transmitter/Receiver For preliminary testing of our transmitter/receiver network, we sent a 5V peak to peak square wave from the function generator to the transmitter. Figure C.2 shows the output of the receiver, which confirmed that our transmission was successful. Our signal strength was also relatively strong within the Senior Design Lab. Next, we tried to send data from the PIC to the transmitter. This was relatively easy because the putc( ) built-in-function on the PIC basically sends the 8 bits serially. When this was successful, we implemented user identification in a similar manner. Figure C.3 shows the output of the receiver, which displays a user ID and the answer. A low bit is always the start bit because the receiver is high when the transmitter is not sending anything. Finally, to test for a long distance, we took our circuit to test from one end of the EL Second Floor Hallway to the other. We found that our signal strength was relatively weak but can be improved by using antennas with higher gain.

5. COST

This product is designed to improve class participation. Each classroom would need only one receiving device, and as many input devices as there are students. A mass production cost analysis is included for a classroom with 1000 students. 5.1 Parts Our most expensive parts for the Input and Receiving Devices were the transmitters and receivers. For our design, we chose to use Linx Technologies HP-3 Series. If instead we used a less expensive transmitter/receiver such as the LC Series6,7, we would save a considerable amount of money. We ended up with a total cost for one Input Device and one Receiving Device of $202.94 and a mass production cost for 1000 Input Devices and one Receiving Device of $92,180.25. If we had used the LC Series, our total cost would have been approximately $123.34 with a mass production cost of $57,685.13. The cost analysis can be seen on Tables D.1 to D.4 in Appendix D. The analysis shows the single production cost and the mass production cost for both the HP-3 Series and LC Series transmitter/receivers. 5.2 Labor We estimated our salary to be around $50/hour. We spent around 130 hours each researching, developing, and debugging our product. Using Equation 5.1 below, we calculated the labor cost to be $32,500. Labor Cost = (Ideal Hourly Salary ´ (Hours Spent) ´ 2.5) (5.1) (2.1)

6. CONCLUSIONS

We were happy with our project’s success. We were able to take in the student’s input and transmit it onto the professor’s computer. Our feedback features (the LEDs and the LCD) also proved to be useful according to our surveyed students. We met all three of our performance requirements. The Red LED illuminates when data is successfully transmitted and the Green LED illuminates when the data is successfully received. Our response time is well under the 2 second performance requirement. In fact, the LEDs indicate the response time is virtually instantaneous. The distance requirement was also met through our testing across the second floor of Everitt Lab. We determined that the 200 ft range was the maximum distance with our current antennas. There are several future improvements that can be made to our design. First, antennas with higher gain can maximize our transmitting range. We found that the antennas we used had some difficulty transmitting across the length of Everitt Lab. Half wavelength antennas may be able to cure these inconsistencies. Second, we would like to make our input device battery powered. We have calculated a power analysis in Appendix F which shows that the device would last 48 hours with Energizer AA batteries. The battery life analysis utilized data from [8], [9], and [10]. With a battery powered device, it would be necessary to implement a power save feature. After implementing the power save feature, the battery life would be sufficient. We would also like to make the device more portable by building the circuit on a PCB. This change may slightly increase the cost, but we feel it would make the product more marketable. From our surveyed students, we also found that multiple digit submissions would be a desirable feature that we can add in future work. This change would be a simple PIC code alteration. The HP-3 series transmitters and receivers contain more functionality than necessary for our design, and therefore added unnecessary cost. Our cost analysis shows that the LC Series would be more cost effective for our purposes. Appendix F shows a power analysis for our design with the LC Series transmitter/receiver.

APPENDIX B– SCHEMATICS

Figure B.1: Input Device Schematic

Figure B.2: Receiving Device Schematic

Figure C.2: Transmitter/Receiver, Top: input to transmitter, Bottom: output from receiver Figure C.3: Transmitter/Receiver, output from Receiver 00001110 10101100

Figure C.4: RS 232, HyperTerminal and Excel extraction