Project overview and description
The goal of the environmental sensing module is to be attached to another
piece of equipment and record temperature, humidity, and shock applied to the other piece of equipment. Due to this goal, the environmental sensing module must be relatively small, low power, able to run off a separate power supply, able to store sensor data, and able to connect to peripheral devices. For this reason we used the Altera DE2 board, it comes with a cyclone II Field Programmable Gate Array (FPGA), serial configuration device (EPCS16), four megabytes of flash memory, a 50 or 27 MHz oscillator for clock source, a USB host/slave controller, eight megabytes of synchronous dynamic random access memory (SDRAM), and five hundred and twelve kilobytes of Static RAM (SRAM). Unfortunately it makes the environmental sensing module larger than what we would like, but if we were going to take this to production, we could easily remove the Altera DE2 board and instead use individual components. The sensors are already small enough, even on breakout boards, those coupled with our external power supply, voltage regulator and external clock are small enough to be placed inside another piece of equipment. All of these devices are very low power, which will allow for a longer battery life running on external power. All this coupled with our intention of only keeping extreme data means that the memory on the Altera DE2 board will be more than enough.
Theoretical concept, general design approach and system architecture
In order to accomplish the goal of creating an environmental sensing module we needed to attach two sensors to a microprocessor. The easy part is using the Alter DE2 board. The board requires a power supply greater than all the components so we do not have to worry about individual power for each component as it should be able to be powered by the same source as the Altera DE2 board. Then we connect the sensors to the general I/O ports on the board. The ADXL345 require very few inputs from the microcontroller, just the data and clock signal because we chose to use the I2C connection. The SHT21 will have two serial lines running from the microcontroller to the sensors. These lines are the serial clock input and the serial data lines. Both of these sensors will be connected to the Altera DE2 board via the 40 pin extension headers. The ISL12058 is a low power real time clock that will be used to timestamp events.