We had a few issues along the way. The capacitance sensor was something that we had to build from scratch. So it was a challenge at the beginning. But fortunately we had plenty of help from the professor and TAs, and we were able to solve all the hardware issues. We also encountered some issues on the free keypad. First, we found out that the keypad (from the old project) did not work properly and some of the pins might be malfunctioning. The keys on the bottom row and the rightmost column just don't seem to be detected. This is more of a hardware issue and if we resort to using just the keys other than those malfunctiong ones, such as 2,3,5,6, things work fine. In the end, because we were still under budget, we decided to use the keypad from the lab instead and cost it for another $5. Even after we did this, we are still under budget.
Secondly, we also had some problems with the UART serial connection at the beginning. The system was too slow to respond to some of the functions from the keyboard, due to some unnecessary serial transmission. However things were sorted out when we cleaned up those part in the code that causes this issue.
We also had an issue with the PIR sensor, by having a hard time trying to determine how it actually works. We tried to find out how the output voltage actually relates to the surrounding temperature sensed by the PIR. But even now, the detail operating characteristics of the PIR sensor is still unknown.
Other than those issues mentioned above, most of the design aspects work fine and testing results are fairly accurate. We do testing at each stage to make sure things are good before we move on to the next level. We make sure that all hardware are working properly according to standard before we move on to software. Program codes are also tested at each stage, separately for transmitter side and receiver side. This is to ensure that we don't end up debugging the wrong part and to make sure that errors and bugs are easier to diagnose, if there is any.
This project is safe for usage because it only applies two 9V battery sources and there is no other external factors that could contribute to any safety issues. There may be some RF interference caused by other people's design but our transmitting scheme is fairly robust so it should be able to stand the interference. This project is usable by anyone who wants to put it in a room for the basic purpose of security.