Operation

When originally planning our system design, our display system was an area of contention. We had initially planned to upload our results online through TCPIP server but ultimately we decided to use the AdaFruit Touchscreen LCD we had been using for our labs due to time limit concerns.

Our planned display system included a simple statement letting our user know how many people were currently in the dining hall of their choice. It would also include a visual aid; a listing of each seat at a specific table color coded. Red for unavailable set and Green for one that is available. We decided that this would get the message across simply and effectively.

Display, lit with information

Operation

The Laser Link Body Count system was responsible for monitoring the number of people at any specific point in time at any dining hall employing our system. It uses an ingenious combination of lasers and photoreceptors, two of each, to achieve this, placed one in front of the other. Each laser would be met on the other side by a phototransistor, both placed on one side of monitored dining halls. As people walked into a hall, they would trip the laser, then the other laser. Our microcontroller would record the time at which these two actions occurred and preform some simple algebra to figure out if a person was leaving or not.

• The Laser Link would be placed at least at waist height to make sure people trip the lasers as they walk in and also avoid inaccurate readings from lasers being tripped by two legs from the same person.

Setup and Design

Lasers

The lasers we used were provided by our very own Professor Nadovich instead of the purchases we had already planned. They were the very ones the school used for its audio over laser projects. Setup was achieved through the use of an external 9V battery scaled down to the required value. Though the lasers could have been powered with voltage from our microcontroller, the use of external sources was a design choice we made after consideration of the distance that needed to exist between them and the phototransistors. After getting them setup, we were ready to proceed with the phototransistors.

Laser : Front View

Laser : Back View, alterations made are visible, including altered wiring.

Through very fortuitous, the lasers we acquired were not without their problems. The default wires were very weak, short, frayed, and much too weak to even penetrate our breadboard let alone hold up the relatively heavy lasers; and as such, made testing a right pain. We had to custom-make stands for them through the school hardware shop, and make sure to add extra wire to increase length and use some heat-shrink tubing to enhance their durability. A visual of the modded lasers as well as the accompanying circuit can be seen below.

Laser with Accompanying Circuit

Phototransistors

We were also given some phototransistors to work with by Professor Nadovich. These served as the other half to the system by detecting the lasers and sensing when they were tripped. They ran on power supplies in the range of 1.8V to 5.5V, which could easily be supplied by our microcontroller. When not detecting the phototransistors defaulted to outputting 0V, and output a voltage of 3.3V when detecting the lasers. Setup of the phototransistors included the use of an MCP6242 op-amp comparator for getting more precise outputs for aid in calculations.

After setup was completed, testing was relatively straight-forward. We monitored the photo receptor output voltage from the phototransistors through oscilloscope to make sure expected operation was achieved and verified that it was. The scope-capture below shows our two phototransistors tripped one after another; each outputting a voltage of 3.3V for the duration and returning their default 0V output after.

Week 4

This last week of the project saw us take the final steps to finish up the functionality of our project. Our main goals for this week were as follows:

• Pick up hardware implementation gadgets we had made by the hardware shop including laser mounts and guards for the motion sensors.
• Implement testing using the gadgets.
• Setup and finalize the project functionality.

Laser Mounts

On Thursday, we received our laser mounts from the hardware shop. These were designed and requested by Preston in week 3. The mounts greatly improved our testing procedure as they brought an extra degree of stability that was welcome. The mounts are pictured below.

In addition. Raji resoldered the connections to the lasers for length and a sturdier connection. Heat shrink tubing was also used to cover the joints between the two different wires. This process required a soldering iron, 24 gauge wire and an heat gun.

Sensor Limiter

On Friday, we received acrylic tubes we had requested from the hardware shop to limit the sensitivity scope of our Motion Sensors. The sensors initially had a spherical scope that was much too wide for the application we had in mind. Our plans were to suspend motion sensors above each seat at the table to be monitored and the relatively large default scope would keep picking up readings from other seats. To combat this, we used the tubes to limit the scope of the sensors strictly downward. The Sensor + Tube setup in question are presented below.

From Top                                                                       From Front

Mounted Hardware Sensor Testing

Laser Link

After installing the lasers into our mounts and positioning the phototransistors and the corresponding circuits in place, we ran some hardware tests. Results were as expected. The phototransistors have a low voltage output if detecting the laser and vice versa, by blocking the laser a high output is observed. Scope output results from the phototransistors are shown below are shown below.

• The picture shows the output from the Laser link circuit as Preston walked through simulating a person walking through a door. The first pulse is the front laser being broken, and the second pulse corresponds to the second laser.

Motion Sensors

Raji ran similar tests with the adjusted Motion Sensors and we got the expected results. A low signal is output from the sensor when nothing has been detected in the field of view and a high is output for a duration of 10 secs when movement is detected. We are using this property to determining if the seat being monitored is empty or not.

Putting it Together

Preston built the voltage regulator/laser and phototransistor circuits of the project. The former being the “transmitter” and the latter the “receiver”. The voltage regulator used a LM317TO-220 which stepped the 9V battery down to ~3.3 for the laser. The phototransistor circuits outputted a high voltage (3.3V) when the laser link was blocked. This is similar to the circuitry implemented in lab 5.

Having gotten successful hardware testing out of the way, for the final part of this week, we focused out efforts on the software side of things. We used the outputs from our laser link to trigger interrupts and figure out if somebody was going or leaving. And we used our motion sensors to monitor table activity. The interrupts have been giving us severe trouble however not triggering when expected.

Our goal for last week was to make progress on the software side of our project including the Laser Triggering setup, the LCD outputs and the Motion Sensor control operational. We also aimed to get significant work done on the Motion Sensor setup that will be used to monitor individuals at tables. In addition, we ran into some problems with the photo-detector output current we had to fix.

• The photo-detector we were using for our Lasor Link was outputting currents that were not allowable by the PIC, to fix this, we used the same MCP6242 Op-Amp setup used in Lab 5. A picture of the setup follows below.

Our second task this week was the software side of our project. The following tasks were achieved in regards to this.

• Configured Timer for Photo-transistor interrupts
• Configured input capture & interrupts for Photo-transistor input. We are now able to determine if a person just entered the room or left.
• Configured motion sensor input to the PIC and the timer. If any motion has been detected around the seat we are monitoring within the last 5 minutes, we can conclude that that seat is occupied.
• Configured various proto-threads
• Configured LCD to display the current number of people in the room.

Our plans for next week are as follows.

• Obtain a stable mount for the laser link
• Tune sensitivity of the motion sensor
• Finalize table occupancy graphics on LCD
• Obtain motion sensor mounts