Introduction: MSPF Common Ground

Common Ground was a sidewalk installation designed by Cloud Arch Studio for the Market Street Prototyping Festival. Please start by watching the video made by Autodesk, and then continue to learn more about how we made it!

Please feel free to contact us at with any more questions!

Step 1: Step 1: Materials

To construct Common Ground structure we used the following:

  • 2x2's, about 500 lf
  • 3/4"x3/4", 36 lf
  • 3/4" ply, about 150 sqft
  • Reclaimed redwood siding (or other finish of your choice), about 300 lf
  • Plastic sheeting, about 50 sqft
  • 1" foam, about 25 sqft
  • PP53006 submersible fountain pump from PonicsPumps, x12
  • 3/4" PVC pipe at 12", 18", and 24" lengths, x4
  • 3/4" PVC street elbow, x24
  • 3/4" to 5/8" or less nipple, x12
  • 5 gal bucket, x12
  • 4" drainage cap, x12
  • White exterior satin enamel paint
  • Screws, staples, glue
  • Gravel or rocks
  • Landscaping
  • Water, about 60 gallons every day
  • (Optional) Waterproof LED fountain light, x12

For the control system we used the following:

  • Limit switch, x18
  • Arduino Mega 2560, x1
  • Octocoupled relay, 4A, x12
  • Solid core wire, about 250 lf
  • 1.8"x7" DIP solder board, x6
  • Garbage disposal cord, x12
  • Male and female Molex connectors, 2-pin and 3-pin
  • Duplex outlet, x6
  • 3.3 K resistor, x18
  • 4-40 threaded inserts
  • Audio jack, female and male, x18 each
  • 1/8" Acrylic sheets, about 10 sqft
  • Screws, electrical tape, solder, glue
  • Power strips and extension cords

Step 2: Step 2: Design

Our design concept was an active game that requires participation from two or more strangers. We chose switch-based panels for their accessibility by all pedestrians, whether they were kids, adults, handicapped, in a stroller, or on a bike. We chose the activated feature to be a water fountain because of its visual effect (in practice this can be a light, sound, or kinematic feature of any type). We wrapped all these features together into an elegant landscape complete with plants and reclaimed redwood to appear warm and inviting on the street.

Given eighteen digital inputs (one for each panel), the electronic control system needed to be able to switch not only twelve different pumps but also twelve different lights for nighttime operation. We used limit switches to sense whether or not someone had stepped on a panel, and we selected an Arduino Mega 2560 to control the system because of its abundance of digital I/O pins. We decided to switch twelve wall outlets so that any device with a wall plug could be switched by our system, and we used optocoupled relays to isolate the wall circuitry from the Arduino circuitry.

With the help of the Market Street Prototyping Festival team, we were able to get feedback from the public in two prototyping sessions. Based on their ideas, we were able to settle on the final number of features and their undulating geometry, as well as the use of natural materials.

To design Common Ground we primarily used SketchUp and hand drawing. We also built many prototypes at full scale to test the basic interaction. Our design captain, Autodesk, gave invaluable advice throughout the design process.

Our specific prototype was designed for the specific constraints and guidelines of the festival, but we see the concept of Common Ground being scalable and infinitely adaptable to the urban landscape. If San Francisco were to pursue this concept, we would tailor each Common Ground to its unique location and provide a myriad of magical moments all throughout the city.

Step 3: Step 3: Fabrication

Once we felt confident in our design, we started fabricating the real structure and control system. This process took roughly 150 man hours.

The wooden structure was constructed using 2x2 frame construction and plywood sheeting. The structure has four main sections:

  1. Sidewalk panel, 12 2'x2' plywood pavers framed in by 2x2's
  2. Planters, 4'x12'x2' frame upon which individually heighted boxes can be placed
  3. Step area, 2'x12'x1' frame with decking
  4. Seating area, 2'x12'x3' frame with 6 2'x2' redwood seat panels

These pieces should be kept separate for easy assembly/reassembly.

The panels on the sidewalk and seating sections should be 3/4" plywood with 3/4"x3/4" joists below. In the remaining spaces between the joists, 1" foam should be added so that the entire panel can displace about 1/4" when stepped on. Right in the center of the panel, a switch should be screwed into the side of a joist. The switch should be connected to an adequate length of wire to reach the control box. More information about the control system can be found below.

The planter boxes themselves are constructed of plywood or OSB and sided with the finish of choice. On the top face plastic sheeting is placed under the edge trim for drainage into a 4" hole in the center, which is capped with a drainage cap (with an widened hole). This allows for water that shoots out of the fountain to drain back into the bucket.

The buckets will be installed on site, but the pumps should be prepared with PVC pipe nozzles to the desired height such that the tip of the nozzle will just penetrate the drainage cap.

Each set of panels (two pavers, one seat) requires its own circuit board. Each board consists of three switch inputs, corresponding outputs for the Arduino to sense the switches, two optocoupled relays (one for each outlet to be controlled), two inputs from the Arduino to control the relays, 5V power and ground inputs for the small-signal circuitry, and 120V high, neutral, and ground inputs for the power circuitry. Six copies of this board should be manually soldered, in addition to a power distribution board. An acrylic box should be laser cut with appropriately spaced mounting holes for all the outlets, switches, and circuitry.

Step 4: Step 4: Installation

Once the entire structure was fabricated off-site, we were ready to disassemble, transport, and reassemble Common Ground on Market Street for the festival.

We rented a 15' U-HAUL truck and strapped in all the individual pieces. Once we got to Market Street we put all the pieces back together again with clamps. The order of the pieces should be as follows:

  1. Planter base
  2. Sidewalk panels (feeding wires through planter base)
  3. Buckets with pumps (feeding wires through planter base)
  4. Step area
  5. Seating area
  6. Planter boxes (feeding nozzles through openings)
  7. Control box (plugging in all wires and cords)
  8. Plants and landscaping
  9. Add water

The control box should be tested before any power is brought to the box by plugging the Arduino into a laptop and checking for signals from all of the 18 limit switches. The pumps can also each be tested manually by plugging its cord directly into a power source just to check that the pumps are working properly. Finally, the entire control system can be plugged into a power source and Common Ground is ready to go.

Step 5: Step 5: Interaction

Common Ground was a huge success at the Market Street Prototyping Festival. From the moment we went live, the installation drew delighted crowds, especially kids. We discovered that Common Ground was especially good at connecting strangers in cooperative play, as well as helping kids open up to express themselves. Even dogs found the installation fun.

We found that due to the wind and inaccurate alignment of the nozzles, we started to run out of water in certain buckets after a few hours. Of course in a real installation there would be little to no water loss, but in our case we had to get access to a municipal water source and refill specific buckets with a water hose. We also found that some of the panels had to have their foam replaced after a day of use. Some of the plants also wilted from the excessive watering, so we had to replace plants after a day. At the end of each day we disconnected the control box from its power source and put a tarp over the installation since we didn't want to leave the wires exposed.

On the last night, we decided to have some fun and show an alternative form of Common Ground that didn't require water. We swapped out all the pumps for lights and found this version to be just as engaging.

We look forward to the opportunity to develop this prototyping and implement it in San Francisco and cities all around the world! Please feel free to contact us at with any more questions!