Design Project



Theory of Operation

Power Supply:

A +12VDC supply from the solar car provides power to the driver interface board, which is stepped down to +5VDC using a switching regulator LTC1174-5 [1] configured to provide current up to 600mA . The estimated power consumption of the driver interface board, with the LCD backlight on 100%, is less than 2.25W (450mA at 5VDC) so there is plenty of margin in the power supply design. The +5VDC supply was chosen to simplify the power requirements since all of the peripherals where also chosen to support at +5VDC supply. Decoupling is provided in accordance with [1] Low ESR surface mount capacitors.

Microcontroller:

The PIC18F4680 [2] microcontroller was chosen for this project. The PIC microcontrollers provide In-Circuit Serial Programming (ICSP) capability using just 3 pins on the microcontroller which are brought out to a header. The microcontroller receives the input of a 10MHz crystal and then will use a PLL to achieve desired operating frequency which will be determined by the solar team to balance needed frequency with the power considerations. The crystal load circuit is configured as shown in the PIC datasheet previously referenced. The user input (except the RPG) is received through the SPI port which is connected to the PLD. The LCD is driven by I2C which can share the SPI port as shown in [3]. In the case that this method causes problems, additional circuitry is provided to allow the SPI interface to be implemented on general purpose I/O. The microcontroller also provides PWM signals to manage the on-board LED brightness to help conserve power. The on-chip A/D is used to check supply voltage level and read the voltage from a temperature sensor. Regular I/O is used for the cable detect signals for the CAN connections and the RS-232 connection. In order to provide debug support, an RS-232 interface is provided. Decoupling is provided in accordance with the recommendations by Microchip [4].

.

LCD Interface:

The LCD interface [6] is an I2C interface to be implemented on the SPI bus as previously described. The two I2C pins and power and ground are brought to a header since the LCD module will be mounted away from the board. Backlight management and LCD contrast are controlled in software by commands from the microcontroller to the LCD controller.

User Interface:

The user interface consists of an RPG with an integrated select button, and up to four other buttons. Since space is limited on the steering wheel in the solar car, there will only be 2 buttons and the RPG available to the driver while driving and the other 2 buttons will be available for future expansion. Because the buttons will be mounted away from the enclosure and routed through a wiring harness, optical isolation is provided as a precautionary measure to protect the microcontroller and PLD from damage.

Analog:

This product has very little contact with the analog world, but there is a temperature sensor (LM19CIZ [7]) that provides a linear output voltage dependant on the ambient temperature as well as a photosensor that produces a changing resistance (from 8KOhms to 16KOhms) in response to the amount of ambient light. This will allow dynamic LCD backlight control since the microcontroller will have information about the brightness in the cockpit of the car and adjust the backlight accordingly (this feature can also be disabled by the operator).

Indicators:

LEDs:

There are 9 LEDs on the circuit board which will provide functionality as described below. A green LED will light when power (5VDC) is applied to the circuit, a second LED will blink alternating between red and green to show microprocessor operation (watchdog), a third will light green to denote debug mode (serial cable plugged in), and the six remaining will be available for debug and status purposes and have three of each color (red and green). With the exception of the watchdog and power LEDs, the LEDs are configured in two banks in common anode configuration and a PWM signal is supplied to each of the banks to control brightness. The two PWM signals will be out of phase by 180 degrees so that only one bank of LEDs will be lit at any one time to minimize power consumption.

Buzzer:

A 12VDC buzzer with integrated drive circuitry is provided to provide additional alerts to the driver of important information or errors. The LCD backlight can also be strobed to provide visual alerts.

2. Summary

The preceding circuit description shows how the circuitry was constructed to achieve the desired operation for the driver interface. The power supply, microcontroller, LCD, and user interface have all been glued together with interface logic to build the complete system. A number of decisions were made in an effort to reduce the power consumption of this product while still providing the desired functionality. Enclosed below are the Bill of Materials (BOM) and the output of the schematic Design Rule Check (DRC). As noted below, the errors and warnings that show up on the DRC are not really errors but part of the design or symbol differences which do not affect the functionality of the design.

List of References

1]

2]

3]

4]

5]

6]

7]

Appendix A: Design Rule Check Report

All warnings and errors were checked and do not present a problem.

--------------------------------------------------

Checking Schematic: Team14

--------------------------------------------------

Checking Electrical Rules

ERROR: [DRC0003] Port has a type which is inconsistent with other ports on the net XTAL1

Team14, Microcontroller and PLD (4.70, 3.50)

ERROR: [DRC0003] Port has a type which is inconsistent with other ports on the net XTAL1

Team14, Microcontroller and PLD (2.90, 9.50)

ERROR: [DRC0003] Port has a type which is inconsistent with other ports on the net XTAL2

Team14, Microcontroller and PLD (4.70, 3.60)

ERROR: [DRC0003] Port has a type which is inconsistent with other ports on the net XTAL2

Team14, Microcontroller and PLD (1.30, 9.60)

ERROR: [DRC0004] Possible pin type conflict 5VDC Input Port Connected to Power

Team14, Microcontroller and PLD (1.30, 8.00)

ERROR: [DRC0004] Possible pin type conflict 5VDC Input Port Connected to Power

Team14, Microcontroller and PLD (2.90, 9.40)

ERROR: [DRC0004] Possible pin type conflict U3,Vdd Power Connected to Input Port

Team14, Microcontroller and PLD (6.80, 2.40)

ERROR: [DRC0004] Possible pin type conflict U6,VCC Power Connected to Input Port

Team14, Microcontroller and PLD (14.10, 2.00)

ERROR: [DRC0004] Possible pin type conflict U1,VOUT Output Connected to Input Port

Team14, Power And Communication (4.50, 1.40)

ERROR: [DRC0004] Possible pin type conflict U1,VOUT Output Connected to Power

Team14, Power And Communication (4.50, 1.40)

ERROR: [DRC0004] Possible pin type conflict GND Input Port Connected to Power

Team14, Microcontroller and PLD (1.30, 9.50)

ERROR: [DRC0004] Possible pin type conflict GND Input Port Connected to Power

Team14, Microcontroller and PLD (2.90, 7.90)

ERROR: [DRC0004] Possible pin type conflict U3,Vss Power Connected to Input Port

Team14, Microcontroller and PLD (6.80, 6.10)

ERROR: [DRC0004] Possible pin type conflict U10,gnd Power Connected to Input Port

Team14, Power And Communication (14.40, 8.80)

WARNING: [DRC0005] Unconnected pin U5,T2IN

Team14, Power And Communication (11.40, 6.50)

WARNING: [DRC0005] Unconnected pin U5,R2IN

Team14, Power And Communication (11.40, 6.20)

Checking for Unconnected Nets

WARNING: [DRC0007] Net has no driving source N51844

Team14, Microcontroller and PLD (14.71, 2.30)

WARNING: [DRC0006] Net has fewer than two connections N51844

Team14, Microcontroller and PLD (14.71, 2.30)

Checking for Invalid References

Checking for Duplicate References

Check Bus width mismatch

Appendix B: Bill of Materials Report

|ECE477 Team14 LEDs Optos and Misc Block Revised: Friday, February 24, 2006 |

|2 Revision: 1.5 | | | |

| | | | | | |

|Team 14 | | | | |

| | | | | | |

|Bill Of Materials February 24,2006 11:25:45 | | |

| | | | | | |

| | | | | | |

| | | | | | |

| | | | | | |

| | | | | | |

|Item |Quantity |Reference |Part | | |

|______________________________________________ | | |

| | | | | | |

|1 |1 |C1 |100uF | | |

|2 |2 |C2,C3 |22pF | | |

|3 |10 |C4,C8,C9,C10,C11,C12,C13, |0.1uF | | |

| | |C14,C15,C16 | | | |

|4 |3 |C5,C6,C7 |15uF | | |

|5 |1 |D2 |1n5818 | | |

|6 |6 |D3,D4,D5,D6,D7,D8 |dualLED | | |

|7 |7 |ISO1,ISO2,ISO3,ISO4,ISO5, |OPTO ISOLATOR-A |

| | |ISO6,ISO7 | | | |

|8 |2 |J1,J14 |CAN | | |

|9 |1 |J2 |Programming Header |

|10 |1 |J3 |LCD Interface | |

|11 |1 |J4 |12Vdc Input | |

|12 |1 |J5 |RS232, DB-9 | |

|13 |4 |J6,J7,J8,J9 |CON12A | |

|14 |1 |J10 |CON14 | | |

|15 |1 |J11 |ispGAL programmer |

|16 |1 |J12 |Extra I/O | |

|17 |1 |J13 |Light Detect | |

|18 |1 |L1 |100uH | | |

|19 |2 |Q1,Q2 |PNP BCE | |

|20 |1 |Q3 |NPN BCE | |

|21 |7 |R1,R2,R5,R6,R10,R11,R43 |10K | | |

|22 |2 |R3,R42 |300 | | |

|23 |11 |R4,R7,R8,R9,R12,R13,R14, |0 | | |

| | |R15,R16,R44,R45 | | | |

|24 |10 |R17,R18,R19,R20,R21,R22, |330 | | |

| | |R23,R38,R39,R40 | | | |

|25 |12 |R24,R25,R26,R27,R28,R31, |5K | | |

| | |R32,R33,R34,R35,R36,R37 | | | |

|26 |2 |R29,R30 |3.3K | | |

|27 |1 |R41 |16K | | |

|28 |1 |R46 |1k | | |

|29 |1 |U1 |LTC1174- 5/SO | |

|30 |1 |U2 |MCP2551I/SN | |

|31 |1 |U3 |PIC18F4680-I/PT | |

|32 |1 |U5 |MAX232A/SO | |

|33 |1 |U6 |ISPGAL22V10C/LCC |

|34 |1 |U7 |Buzzer | | |

|35 |1 |U8 |LM19CIZ | |

|36 |4 |U9,U10,U11,U12 |mounting hole | |

|37 |1 |Y1 |CRYSTAL/SM | |

-----------------------

IMPORTANT: Use standard IEEE format for references, and CITE ALL REFERENCES listed in the body of your report. Provide “live” links to all data sheets utilized.

................
................

In order to avoid copyright disputes, this page is only a partial summary.

Google Online Preview   Download