A good cents exit survey

A Penny for Your Thoughts

© Lead Image © olegdudko, 123RF.com

© Lead Image © olegdudko, 123RF.com

Article from Issue 216/2018

Get feedback for live events with an exit survey that counts pennies.

To generate useful feedback for live programs at the Fort Worth Museum of Science & History's Noble Planetarium on the campus of Central Texas College in Killeen, Texas, we conceived, designed, and built a custom feedback system centered around pennies. The goals were (1) ease of use for both guests and staff, (2) a fast participation process, and (3) immediate feedback to the presenters and managers.

The Guest Experience

When you attend a planetarium show at the Noble Planetarium, you are handed a penny on the way into the theater. As a part of the show, we ask you to hold out the penny at arm's length and imagine that you are looking through Abraham Lincoln's eye. That approximates the field of view of the Hubble Space Telescope, which is the frame of reference for the remainder of the program.

As you exit the theater, the presenter has rolled out an interesting device that looks sort of like a coin bank (Figure 1). You are invited to return the penny in one of five slots to indicate how much you liked the show. As the pennies are returned, they are tallied by the machine; once everyone has exited, the presenter submits the counts, which are immediately visible on an internal web page.

Figure 1: The Penny Counter on the planetarium console ready to accept pennies. Different locations were tested to see whether response levels changed. Staff always step away from the counter as guests are exiting, so they don't influence the ratings.

Hardware and Software

The funnels and case for the penny counter were designed using Blender [1] and printed with a 3D printer [2]. The completed counter is shown in Figure 2.

Figure 2: The Penny Counter after final assembly. Note the captured screws along the back and the nuts visible along the bottom panel.

Under the hood, the Penny Counter's brain is a Raspberry Pi. A two-line by 16-character LCD display shows a menu for the operator; five buttons in a cross pattern provide navigation, and five GPIO pins read infrared sensors at the bottom of each funnel that watch for pennies. The Penny Counter's code is written in Python. It connects to a MySQL database to retrieve show names and post the finished tally after all of the guests have departed.

The Rasp Pi was connected to a generic printed circuit board (PCB) that breaks out the connections from the GPIO header to spring-loaded European-style terminal blocks (Euroblocks), which makes the slot sensors themselves easily interchangeable, as well [3]. The buttons also were wired into spring-loaded Euroblocks. The LCD display was mounted between the buttons and the PCB (Figures 3-6).

Figure 3: The buttons as seen from inside the Penny Counter. Wires were twisted with a power drill to keep each button pair together. The white board is the 2x16 LCD panel. The smaller bundles of blue, white, and green wires are the phototransistor side of the slot sensor. The small red and black wires visible next to each funnel are for the infrared LED illuminating the sensor on the opposite side.
Figure 4: The interconnect PCB. The green blocks on the left are the spring-loaded Euroblock connectors. The blue board on the right is a Rasp Pi GPIO breakout board. The buttons are wired directly to the header because they are not "public-facing" components and therefore not subject to rough handling. The grey ribbon cable connects to the Rasp Pi.
Figure 5: The Rasp Pi and an excellent view of the bottom of the blue funnel. You can just see the network cable in the lower right of the picture. I added the Rasp Pi to the wired network to eliminate connection problems between the Rasp Pi and the museum's wireless network.
Figure 6: The wiring diagram for the Penny Counter.


The Penny Counter is powered by a Python script that monitors the coin slots and buttons and displays information to the user on a small LCD display. The complete penny.py script [4] is available at the Linux Magazine website.

The script begins with several import statements, demonstrating how Python includes libraries with additional functions and methods (Listing 1). The as keyword at the end of lines 4 and 6 creates an alias for easier reference to these modules. The libraries needed for this project are:

Listing 1

Import Statements


  • serial – Allows access to serial ports. In my case, this is a USB device that emulates a serial port.
  • time – Gets current time information.
  • curses – Lets me put text at specific terminal coordinates and captures keypresses. I used this library to simulate the Penny Counter before all of the hardware was built.
  • MySQLdb (mdb) – Accesses MySQL databases.
  • datetime – Gets information about the current date and time and supplies functions to perform calculations.
  • RPi.GPIO (GPIO) – Accesses the 40-pin GPIO header on the Rasp Pi.
  • os – Talks to the underlying operating system on which Python is running. In my case, it is Raspbian, but it could also be Windows or other Linux distributions, depending on your hardware and host system.
  • subprocess – Starts secondary threads for parallel processing.

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