====== Tire Pressure Sensor ======

The pressure is determined by the formula, <m>P=0.145*{{{ADC/2^10}-0.04}/0.0012858}</m> where ADC is the value from the 10-bit DAC and P is the pressure in PSI. The pressure sensor is ratiometric with respect to V<sub>dd</sub> which makes it easy to interface to the PIC. Instead of the LCD display the finished project will use the [[7segdisplay]] to make it easier to read under different lighting conditions. Also, I have not been able to locate a small, backlight display, or even a small single line display that is inexpensive.

===== Prototype =====
{{:projects:electronics:tirepressuresensor:pconbrdtop.jpg?300|}}
{{:projects:electronics:tirepressuresensor:pconbrdbottom.jpg?300|}}
{{:projects:electronics:18f_control_board.jpg?300|}}

{{:projects:electronics:18f_control_board_etch.pdf|}}


===== Parts =====
^  Part#  ^  Description  ^  Source  ^  Cost  ^
|MPX5700DP-ND|0-101.5PSI Pressure sensor|[[http://www.digikey.ca/|Digikey]]|$16|
| |2 Ft 1/4ID hose|Home Hardware|$1.50|
| |2 crimp style hose clamps|Home Hardware|$1.60|
| |Barbed hose connector|Home Hardware|$1.19|
| |Compression fitting|Home Hardware|$1.95|
| |Street Elbow|Home Hardware|$2.29|
| |Barbed hose connector|Home Hardware|$1.19|
| |Click on air chuck for valve stem |Princess Auto|$3|
| |1/8NPT tank valve|Princess Auto|$2.50|
|  Total ||| $<php>print 16+17;</php> |



===== Development =====
Here are the {{:projects:electronics:excel_calculations.pdf|calculations}} I did for the module using a spreadsheet to graph the transfer function, then working out the math to something which can be easily done in assembly.

{{:projects:electronics:mpx5700.pdf|MPX5700 Datasheet}}

{{:projects:electronics:p1020101.jpg?300|}}{{:projects:electronics:7segdisplay:display_working.jpg?300|}}