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Safety Board for a Battery Operated Cooling Unit

Safety Board for a Battery Operated Cooling Unit. Jeffrey Harris Carla A. Swierenga. Outline. Introduction Requirements Benefits Circuit Modules Testing Ethical Concerns. Introduction. The project was to make a safety board for use in a air-conditioned vest

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Safety Board for a Battery Operated Cooling Unit

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  1. Safety Board for a Battery Operated Cooling Unit Jeffrey Harris Carla A. Swierenga

  2. Outline • Introduction • Requirements • Benefits • Circuit • Modules • Testing • Ethical Concerns

  3. Introduction • The project was to make a safety board for use in a air-conditioned vest • A company in the Champaign-Urbana area, Creative Thermal Solutions, provided the requirements

  4. Requirements • Shut down the unit on low voltage (8.3 V) and high current (2 A) • Monitor temperatures for abnormal conditions • LED indicator for fault condition • Onboard programming to adapt to different units

  5. Benefits • Prevent damage to other electrical components • Easily changed for other applications • Troubleshooting aid using fault indication • Compact design

  6. Modules • Voltage Regulator • Over Current Detection • Under Voltage Monitor • Temperature Monitor • Control Logic • LED Signals

  7. Block Diagram

  8. Circuit

  9. Voltage Regulator

  10. Voltage Regulator • Will regulate output voltage to 5 Volts • Powers the PIC, which is used for the Control Logic Module • LM 1117MP -5.0

  11. Voltage Regulator: Testing • The testing process for the voltage regulator involved inputting possible voltages and monitoring the output • The undervoltage module shuts off before 5 V, so having the output be 4.1 is not a problem

  12. Over Current Detection

  13. Over Current Detection • Uses the MAX5932 and IRF 640 chips • A .025 Ω current sensing resistor determines the current. • If over 2 A, sends a signal to the PIC

  14. Under Voltage Monitor

  15. Under Voltage Monitor • Uses the MAX5932 and IRF 640 chips • Will send a signal to the PIC when the voltage gets below 8.3 Volts • When the MAX5932 chip reads in 1.233 V, a low voltage signal is outputted • To get the chip to send a signal at 8.3 V, a voltage divider circuit is used

  16. Under Voltage Monitor • With Vout connected to the MAX chip, the voltage is monitored. Once the voltage to the MAX chip is at 1.233 V, it sends a signal to shutdown the circuit • To get the signal sent when the circuit reaches 8.3 V, the theoretical resistor values had to be around 2k Ω and 11.46kΩ

  17. Under Voltage Monitor • Since we did not have the theoretical values in the lab, various combinations of resistors were tested • 15 k Ω and 2.7 k Ω were the values used in the final design

  18. Temperature Monitor • There will be two temperatures monitored using thermistors • Thermistors are resistors that change resistance based on temperature. • Both of these two will be monitored using thermistors in a voltage divider method. • The wheatstone bridge method was not used.

  19. Temperature Monitor: Wheatstone Bridge • A Wheatstone bridge is one way to find an unknown resistance. • To find the resistance, the voltage must be known at both point B and point D. • This method was not used because it needs two analog inputs per resistor and PIC chosen only had two analog inputs total. • Also, the less wires going from the thermistors to the board the better. Wheatstone Bridge Circuit

  20. Temperature Monitor: Voltage Divider • The thermistor is in the R1 spot and a 10k Ω resistor is in the R2 spot. • Vout is one of the analog inputs to the PIC.

  21. Temperature Monitor • To get the right values for the input to the PIC, different temperature conditions were used to calibrate the PIC • A soldering iron with variable temperature setting was used to find the right values

  22. Temperature Monitor • Testing the thermistors and the ADC together produced the above values • With these values, we were able to estimate the threshold value of 217

  23. Control Logic

  24. Control Logic

  25. Control Logic • The control logic is written in C • The chip used is PIC18F1330 • There are two digital inputs: under voltage and over current • There are two analog inputs: two thermistor readings • The two analog inputs needed to have an Analog to Digital converter in the script • Low pass filter on the analog inputs to ensure fault condition

  26. LED Signals • The LED will blink depending on the different faults. • It will blink between 1 – 4 times, depending on fault, then stop and start again. • LED will continue to blink until the power has been turned off.

  27. Testing • Each Module was tested individually • The entire project was then put together and tested

  28. Ethical Concerns • We have considered the best options for both safety and reliability for our client • We did quality testing to insure the board will do what we claim and met or exceeded expectations

  29. Conclusion • Thanks for listening • Any questions?

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