By Chelsea Mediavilla (Electronic and Control)

This post discusses single event upsets (SEUs) and their effects. The choice in SEU monitor and implementation for the Spring 2016 SPARCCS project is explored.

Table of Contents

Introduction

A single event upset (SEU) occurs when a high energy particle collides with sensitive electronic equipment. The energy required to cause an interrupt varies depending on the device but typically occurs from protons of 10-40MeV. The effects of these collisions generally consist of temporary hiccups in data, or changes in state of a device. Monitoring the frequency of these events is vital in circumstances where high energy is common (space, for example) in order to explain any discrepancies. Missions to space normally rely on advanced SEU monitors such as the European Space Agency’s Standard SEU Monitor. An option of this magnitude, however, is not feasible for the Spring 2016 CubeSat Team due to limits on resources.

SEU Options

The CSULB CubeSat Project provided our team with $250 to produce a completed printed circuit board with the necessary equipment implemented. This budget was to cover the expenses of a high voltage converter, an SEU monitor, RS-422 support circuity, a microcontroller, and miscellaneous circuit components. Because space-grade SEU monitors cost much more than we could allot for the device, the CSULB CubeSat Project suggested our team consider a CCD camera. The use of CCDs, or charge coupled devices, as high energy detectors has been documented in experiments, and thus would act as a reliable guide for our project.

Unfortunately, the camera suggested by the club did not provide enough information or include a datasheet, and thus was not a suitable option for the project. The next best CCD options ranged from $60 to over $200. Through research of CCD cameras, we discovered the commonly compared CMOS camera. While we were unable to find documents supporting the use of CMOS cameras as SEU monitors, we did find that CMOS cellphone cameras were being used as image sensors and radiation detectors. With this in mind, we decided to use these experiments as the basis of our SEU model.

Implementation

The µCam-II was ultimately chosen because of its low cost ($48) and its ideal operating voltage (5 volts). The camera has a built in micro controller that receives and sends data based on the command table provided below:

The camera is meant to work for the 4D systems IDE, but our Geiger counter code is designed in the Arduino IDE. After researching how to send and receive this data using an Arduino, I found an open source library created specifically for the µCAM-II in the Arduino IDE at Github.com. This library was used as the basis of our microcontroller/ micro camera communication. I edited the code from this library to remove unnecessary information collected and outputted by the MCU. I also added a code to filter out the pixels that read at a value of 255 (the max value of one byte); these pixels are considered saturated. This portion of the code is shown below:

In order to differentiate between saturated pixels caused by natural light and those from high energy particles, we covered the camera with insulating black electrical tape. The electrical tapes also filters out weaker high energy particles such as alpha radiation, which allows for detection of higher energy. The number of resulting saturated pixels are then summed and displayed by the microcontroller. An in depth analysis of the µCAM software is discussed in the Software Design blog post.

Conclusion

The Spring 2016 SPARCCS project requires a single event upset monitor included on the final printed circuit board. As suggested by the CSULB CubeSat Project, our team researched multiple CCD options, however, ultimately chose a suitable CMOS camera. The implementation of the camera as an SEU monitor is based on experiments conducted using CCD cameras and CMOS cell phone cameras. The final product reads high energy particles filtered through black electrical tape.