Flexible Hardware Configurations for Studying Mobile Usability
Antti Oulasvirta and Tuomo Nyyssönen
Journal of Usability Studies, Volume 4, Issue 2, February 2009, pp. 93-105
Article Contents
System Description
ARMIv2 is based on experiences and technology from ARMIv1 (Oulasvirta et al. 2005). It highlights the following features:
- Belt-mounted, backpack-mounted, and wireless configurations are supported. All non-camera equipment, except cables, attach to a belt worn by the user or can be placed in a backpack. A third alternative is to use wireless transmitters and let the moderator carry non-camera equipment. However, due to signal interference, this results in poorer video quality especially when outdoors.
- Environmental cameras are supported. Surveillance cameras can be assembled to different places of the study site and can be switched to on based on signal strength (Figure 2). These cameras offer a very high image quality and their number is not limited. This enables us to run studies where users can move about autonomously without a shadower. Alternatively, we can also run a study with moderator-controlled cameras (Figure 4).
- Wireless and wired transfer are both supported. All cameras can operate either with cables or wirelessly.
Figure 2. From left to right: All non-camera equipment attaches to a black leather belt worn by the user. In this setup the front camera is in a small black box (a necklace). (b) A lightweight pole attachable to almost any mobile device can host two minicameras; one camera capturing the face of the user, the other camera capturing the events on the display and keyboard. (c) Environmental cameras allow for higher quality third-person views. The receiver switches to the nearest camera automatically based on signal strength.
To our knowledge, these three are novel features in comparison to previous systems. The following are several other improvements that have been made in comparison to ARMIv1:
- Higher quality integrated video. New, compact MPEG-4 recorders provide the advantages of on-the-fly encoding, quick data transfer, and post-trial delivery via USB. Maximum recording times are about ten times longer than a cassette recording. Lower power consumption, price, and smaller size also promote these recorders. ARMIv1's original video quad was replaced by the smallest digital quad available. It was custom-built into a more compact and usable video hub with a smaller die cast aluminum housing and integrated power and camera signal connectors. With the integrated connectors on the hub and cameras it is easy to use one to four cameras and arrange them into the quad view simply by unplugging and plugging them into different inputs. This combination of a recorder and a hub results in 234 kbps AVI files, with a resolution of 640 x 544, a frame rate of about 17 fps, and a MS ADPCM 180 kbps 4 bit audio sound track.
- Increased operational duration (optimally up to 4 hours without a battery change). In practice we reached about 2.5 to 3.0 hours, which is a significant increase in comparison to previous systems. LiLiPUT (Schusterisch et al., 2007) and ARMIv1 both achieved about 90 minutes.
- Lower weight. Due to using hand-crafted casings and generally the smallest available components, the user-worn system part weighs less than 2 kgs. The previous version required the user to carry a backpack of about 4 kgs. LiLiPUT's user-worn part weighs about the same, but includes less functionality.
Figure 3 conveys the system architecture. The stabile part is marked with dark grey coloring; all receivers for A/V data can be either wireless or wired.