We have created a prototype Open APS device that would be installed at the North-East corner of 7th Ave and 23rd Ave W, for the crosswalk across 23rd Ave W.

Open APS map



The prototype is an black acrylic box measuring 6” x 6” x 2”, with a black 6” x 6” anodized aluminum sign face on the front. Behind the sign, there are two push buttons which can detect whether the sign is being pressed. The box is laser-cut, and includes small holes for the buttons to snugly fit (they are soldered through the backside). There are speakers mounted inside the base of the box, which has a grill for audio.

The sign is laser-etched. We also glue a laser-etched piece of black acrylic for braille (spelling out the street name) and tactile white acrylic arrow.

Prototype bottom

On the top of the box, there are two LEDs on the top of the box which correspond to the Walk / Don’t Walk pedestrian light. There is also an etched arrow pointing north (for wayfinding guidance) and a QR code with a unique ID associated with the APS.

Prototype top QR code, id

Inside the device, there is a Raspberry Pi computer; wires to the LEDs and buttons; and speakers. The computer is powered by USB. In our demo, the computer uses a pre-defined intersection timing, but in the real world wires would connect the computer to the intersection signals so our device would always mirror the actual pedestrian signal.

Computer and wires in the prototype


The box emits audio beeps (walk, don’t walk) and also plays synthesized human voice instructions. We detect short- and long-press events (long-press is used to get additional intersection information). Example sounds include:



Don’t Walk, long press (full information):

QR Code and Unique ID

Each device is assigned a unique UI. This is etched as a QR code on the top. This can serve a number of useful functions:

  • Maintenance and inventory control
  • The public can use the QR code to lookup information about NYC APS program, or to report issues
  • We can provide an API for the QR code to give precise location information, which could be used for e.g. mobile accessibility applications.

BLE Beacon

Our prototype emits a Bluetooth Low-Energy (BLE) read-only beacon to advertise its physical position and unique ID. A smartphone within 2 meters can detect the presence of our device, and the signal strength helps a person find the device. Our beacon identifier includes all the information needed to get precise GPS coordinates, crosswalk information, etc.

No Internet Connection

As currently envisioned, our device does not have an internet connection. This simplifies installation, and reduces the potential security risks of having a device which hackers could access wirelessly.

That being said, we could enable a WiFi connection (over a secure VPN) to enable over-the-air updates, or to transmit usage metrics. Alternatively, we could use a cellular SIM card; these are easier to install (no WiFi mesh required) but typically a cost at least $1/mo per device.

Prototype Future Features

We intend to add vibration to the device, too, for when the crosswalk is safe. This assists deaf-blind people as well as blind people when the environment is noisy.

Some other ideas we have considered include:

  • Plug-in audio connection
  • Multilingual support
  • Detect nearby low-vision or blind pedestrians (based on their cell phones emitting a pre-registered signal) to increase locator volume, and pre-configure language settings
  • Transmit intersection status data (walk, don’t walk) for connected apps

Laser Cutting

Our device was generated from these vector graphic (SVG) files which were cut by laser cutter. These vector graphics can easily be auto-generated, and used by anyone with access to a CNC laser cutter, router, or milling machine.

Sign Vector Graphic

Box Vector Graphic

Here is a time-lapse video of a Glowforge consumer laser cutter, creating the box using the above cut plan.

Low Cost

Our total cost of goods was $66:

  • Raspberry Pi: $40
  • 1Gb MicroSD card: $5
  • Acrylic: $4
  • Anodized aluminum: $6
  • Speakers: $11

Note that at scale, these COGs would be significantly lower; and also, we assume that the enclosure and electronics would most likely be mass-produced and pre-assembled.