Smart Table Top

Here is a short video to show you what you will be creating!

For Table Top

• 4 sheets of plexiglass/acrylic
• Weld On 3
• Frosted Finish Spray Paint
• Black Acrylic Paint
• Mod Podge
• Command Strips

Electronics

• Addressable RBG LED strips
• Load Cell Weighing Sensors (We used these)
• HX711 A/D Amplifier Weight Module (We used the one that came with he load cells, here)
• Arduino Uno

The Smart Table Top is designed for restaurants to alert waiters of how full each customer’s drink is to improve efficiency and prevent thirsty customers.

The tabletop can fit on top of any restaurant table and will have coaster built into them that have load cells embedded. These send an analog input based on weight back to an embedded arduino which will then illuminate an LED strip signalling different weights left in a drink depending on the color. Red being needs to be refilled, yellow meaning a refill may need to occur soon, and red meaning the drink is full.

Our idea for this project went through many different iterations. At first, the idea was to create and entire table that would change colors. This would just be for individuals to use at their houses Then, after realizing that was too big, we came up with the idea of creating coasters. If we wanted to use these coasters to assist waiters at restaurants, we realized that these would not be big enough. Finally, we found a perfect solution: a table top. This was a flexible solution that could be implemented at many different locations, and we believe that the lights would be large enough to see from a distance, unlike a coaster.

To begin this project, we started with a cardboard prototype. To do this, we used the same laser cut design we were going to use for our final project. We then taped together the cardboard using simple scotch tape that could be easily removed to change the position of the cardboard.

Prototyping was helpful because we realized we had not allowed enough tolerance between the table we were using and the hole in the bottom of the prototype. Thankfully, we were able to adjust the measurements to ensure that the actual design would fit on top of our selected table.

The second step, after we ensured our prototype's dimensions were correct was to laser cut the actual plexiglass/acrylic. The PDFs we uploaded to the laser printer are attached. Pictures of those files are also included.

We then used Weld on 3 (photos included) to carefully weld the pieces of laser cut plexiglass together. We began with the bottom, sides and support. Then we added the top. We then used 120 grit sandpaper on the inner rectangle to give the clear plexiglass a frosted, more polished look. After that to ensure the frosted look we coated the outside of the whole box with a frosted spray paint.

To create the coasters on the table, we used the acrylic circles that were cut out of the table top sheet of acrylic. We did not remove the safety paper attacked and instead and painted it black. To dry the paint faster since many layers of paint were applied we used a heat gun. After the black paint dried, we then applied a layer of Mod Podge to add a glossy finish.

Finally, we put our tabletop on top of a small green cabinet we were using for our base and for the final finished project covered the cabinet with a black plastic table cloth.

For the brains of this project, you will need to use load cells that will take input from the weight of the cup and communicate that with Arduino. If you choose to buy "2 Sets 50kg Human Scale Load Cell Weighing Sensor Resistance Strain Half-Bridge Sensor + HX711 A/D Amplifier Weight Module DIY Kit for Arduino" or something similar this guild will be helpful in setting them up: https://circuitjournal.com/50kg-load-cells-with-HX...

However, I DO NOT RECCOMEND BUYING THESE. The wires are extremely fragile and the weights are inconsistent and unreliable.

Instead buy a bar load cell similar to this option on Amazon: https://www.amazon.com/Bolsen-Tech-Portable-Electr...

Although you may spend more time creating a counterbalance platform for the load cell you will spend infinitely less time trying to get the finicky wires and load cells to just simply do their job.

They both use the same amplifier so whichever path you choose to take you will have to do the following steps.

• Solder the 4 wires from the load cell to the A+, A-,E+, and E-
• From here you will want to connect wires to your Arduino on the other end of your amplifier to power, ground, and two pins on your Arduino.
• You can then download the HX711 library to Arduino using this link: https://www.arduinolibraries.info/libraries/hx711...
• If you download it here make sure you move the file to your Arduino library folder.
• From here you can run the calibration sample code to make sure the load cell is sending information.

For this table, we created a load cell platform and then added wooden legs to make it the height of the inside of the table. We then connected it to the Arduino and LEDs. The photos show the internal view of the table and load cell.

ALL OF THE CODE IS LINKED HERE: https://github.com/jennasilverman/smarttabletop.gi...

For the coding portion of this project, you essentially want to create a code that takes the input from the load cell and converts it into usable data for the LEDs. We created a program that takes in ranges of weights from the load cells and indicates to the LED was color it should output. For the table, we used two Arduino Unos and sent ranges in the code to each one. Since the load cells were reading different values we essentially have different ranges for each cell. These files are labeled "Final 1" and "Final 2" in the repository. They both do the same things just use different ranges. Also in this repository is a file that tests to confirm that the load cell is properly set up and is sending input to the Arduino.

In order to assemble the tabletop, we pushed two tables together and used the large hole underneath to gain access to the inside.

To attach all of the electronics to the tabletop, we used a double-sided adhesive tape the was easy to remove or restick if needed but kept a firm hold to the acrylic, unlike many other gluing options.

We used the same adhesive tape to tack down the LEDs inside the table as well (hot glue was tried first but was not strong enough)

We also used the breadboard adhesive that is included to adhere it in place as well.

For the load cells, we did use copious amounts of hot glue to adhere the legs, we didn't want the supports to have any wiggle room side to side as that could affect the counterbalance of the load cells.