The compass is an 8-direction compass which can interface directly to the Altera UP1 board with only pull-up resistors. The thermistor and vibration sensor require an analog-to-digital converter for interfacing.

Internally, the sensor is composed of four Bipolar-Junction-Transistors. When one of the transistors is aligned with its representative direction the BJT goes into saturation (sinking up to 25mA). When the BJT is facing any other direction it is in cutoff. I.e. when the BJT representing North is aligned north it outputs 0 volts, align it in any other direction and it maintains its cutoff collector voltage.

Our compass was designed using a 9V raw power Vcc. The compass power was tested using both a 9V adapter and a 12 V battery pack (8 D batteries); both methods were sufficient to drive the logic 1 & 0 thresholds on the Altera board. The two 10Mohm pull-up resistors are required as a voltage divider and for pulling up the collector voltage while in cut-off.

The output pin connection of the Dinsmore compass is shown in figure 1

The connections for each of the output pins has been implemented and tested successfully with this configuration.

The Dinsmore compass gives

8-way directional sensing. (i.e. when both the North & East internal BJTs go into saturation, the direction is North-East.

The ADS7816 ADC is a 12 bit serial output analog-to-digital converter that requires an external clock and a falling edge select line for conversion.

Each ADS7816 ADC is clocked with a 1.25 MHz clock. From experimentation, we were only able to latch every other bit of the 12 bit ADC in effect treating it as a 6 bit ADC with a resolution of 64 levels. Further testing might allow latching of all 12 bits or you might just want to try another ADC. The hardware interfacing in the reset of this document is still valid regardless of ADC resolution.

adcinfo.vhd

Vibration sensing was done by implementing piezo film vibration mass sensors. Some piezo film properties are

-wide freq. range 0.001Hz to 10^9 Hz

-high dielectric strength (to withstand strong fields)

-high mechanical strength and impact resistant

-moisture resistant

Piezo film sensors convert mechanical energy to electrical energy . Implementing and testing the sensor as shown gives (roughly) 0.2 Vpeak-max (at 0 Vdc) output when the sensor is untouched. Vibrational activity produces voltage overshoots of up to (and sometimes beyound) 5v.

vibadc.vhd

tempadc.vhd

[1] Tennessee Technological University, "debounce.vhd"

http://digital5.ece.tntech.edu/Public/Xilinx/Ex...les/xilinx/calc

http://www.ee.ualberta.ca/~elliott/ee552/studentAppNotes/99w/timer/