1. Critical Air System Pressure Controller Senior Design Project, 2010 Morgan Hespe, Department of Electrical and Computer Engineering Mentor: Dr. Stanislaw Legowski, Professor of Electrical Engineering

2. Project Overview Design a printed circuit board controller Controller will operate 2 air compressors to maintain a desired pressure set by the user

3. Specific Goals/Benefits of Controller Alternates compressor starts to ensure equal run time. On low-pressure start-up, both compressors come on, but starts are staggered to reduce utility demand factor charges. This also reduces facility current inrush and local voltage sags.

4. Specific Goals/Benefits of Controller Monitors compressor performance. Initiates warning or alarm to notify user of faulty compressor. Alarm is interrupt reset. Controller has user adjustable settings through binary dip-switches mounted on board. Settings prominently displayed. Bang-bang controller reacts to large drop in pressure by bringing on 2 nd compressor.

5. Hardware Overview ATmega 16: 40-pin PDIP µController 16 K Bytes In-System Programmable Flash Memory I used 1 A/D channel I used 25 of the available 32 input/output pins System clock was set at 1 MHz via internal RC oscillator A/D system clock was set at 1 MHz/8 = 125 kHz (at 13 cycles per conversion: ~ 10k conversions/ sec) Timer system output compare was used to generate alarm/ warning codes

6. Hardware Overview Pressure Transducer: Typical response time of 100 µ seconds matches A/D setting of the µController Adjustable zero and span from 0 to 150 psi * Analog output voltage 0-10 VDC linearly proportional to pressure 35 mA minimum supply current

7. Hardware Overview (4) 3-digit 7-segment LED Display : ~8mA forward current Bright red display for industrial environments 12 total digits

8. Hardware Overview 4-to-16 line decoder/demultiplexer : Takes 4 bit address from µ Controller to de-assert channel corresponding to 7-segment digit of data to be loaded Maximum propagation delay from address input to output de-assertion is ~30 n seconds at VCC=4.5V 74HC154

9. Hardware Overview User-input settings : (3) 8-bit binary switches “load” user settings into D-type flip-flop latches. Latches are sequentially enabled by the ATmega 16 and read on bused port of ATmega 16 Maximum propagation delay from latch enable to output is ~11 n seconds at VCC=5V and load capacitance of 50 p Farads

10. Hardware Overview LED drivers : (12) BCD to 7-segment drivers take BCD data from ATmega 16 and “load” data at enable from demultiplexer Minimum latch enable pulse width is ~260 n seconds

11. Planning

13. Designing

14. Prototyping, First Tries

15. Designing

16. Results Transducer range was not as expected Propagation timing on bused lines was crucial Heat sink design on voltage regulator a must I learned a lot about IC’s, C-code, µControllers, prototyping, PCB design software, etc.

17. What I would do for next version: Surface mount components LCD display for settings SD card interface to adjust parameters in code