* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download doc - Design Group
War of the currents wikipedia , lookup
Electric power system wikipedia , lookup
Ground loop (electricity) wikipedia , lookup
Ground (electricity) wikipedia , lookup
Three-phase electric power wikipedia , lookup
Stepper motor wikipedia , lookup
Power inverter wikipedia , lookup
Mercury-arc valve wikipedia , lookup
Fault tolerance wikipedia , lookup
Pulse-width modulation wikipedia , lookup
Printed circuit board wikipedia , lookup
Electrical substation wikipedia , lookup
Variable-frequency drive wikipedia , lookup
Power engineering wikipedia , lookup
History of electric power transmission wikipedia , lookup
Distribution management system wikipedia , lookup
Voltage regulator wikipedia , lookup
Schmitt trigger wikipedia , lookup
Surface-mount technology wikipedia , lookup
Stray voltage wikipedia , lookup
Electrical ballast wikipedia , lookup
Voltage optimisation wikipedia , lookup
Power electronics wikipedia , lookup
Surge protector wikipedia , lookup
Resistive opto-isolator wikipedia , lookup
Power MOSFET wikipedia , lookup
Switched-mode power supply wikipedia , lookup
Current source wikipedia , lookup
Buck converter wikipedia , lookup
Mains electricity wikipedia , lookup
Current mirror wikipedia , lookup
ME 218C Electrical Description Watercraft Power Board Description The purpose of this circuit board was to provide the following power outputs from two rechargeable NiCad Battery packs, each supplying a nominal voltage of 7.2V: Power Level Destination 14.4 Volts Water Pump 7.2 Volts Drive Motors 5 Volts Communications Board, XBee Board Schematic Design Calculations LM7805 This component is rated to supply up to 1 Amp of current and will take an input voltage of up to 20 Volts. A conservative estimate for the amount of current being drawn by the 5 volt components on the watercraft are: I total I PICS I XBee I LEDs I LM 324 I LM 339 I iButton I PICS 5mA 3units I XBee 45mA I LEDS 50mA 2 I LM 324 1mA I LM 339 1mA V 3.3V 600A R 5 KOhm I total 165mA I iButton These numbers are very conservative (for instance the XBee PIC will be drawing less than 5mA because it is on 3.3Volts power and the two LEDs will never be on at the same time) and the amount of current drawn is still much less than the maximum allowable value of 1amp. IRLZ34N This component was selected because it has a continuous drain current up to 21 Amps. For this application the following equations was used for calculating the drain current: I drain I total( above) I Motor1 I Motor2 I Pump I total 165mA I motor1 I motor2 5 Amps I pump 3.5 A I Drain 14 Amps As can be seen from this calculation the IRLZ34N is a suitable component for the amount of current. The other consideration when using the component as it was intended was the voltage drop across the component due to the RDS on value of 0.035 (with Vgs of 10 V). Even with the maximum current draw from above of 16Amps the Voltage drop across this transistor will be less around 0.56Volts, which is not high enough for the components to register false high values. If the value were around 1.75V then there would be a cause for concern. 10K resistor This is a pull down resistor on the IRLZ34N. The very low leakage currents of this component makes a 10K resistor suitable for this application. 300 Ohm Resistor This is a current limiting resistor on the LED. The voltage drop across the LED was assumed to be around 2 volts leaving 3 volts to be dropped across the resistor. The following calculations were made: V VLED I LED s R Vs 5Volts VLED 2Volts R 300 I LED 10mA Presistor V * I 3 * 0.01 0.03W 2 pin headers The headers available in the TA area are rated up to 4amps. From ME218B it was known that they could handle higher current values without getting failure. It was assumed they would be okay for this application, since the motors will rarely see stall conditions when turning the propellers in the water. Communications Board Description This circuit board houses the two motor drive PICs and acts as a junction point for all the ancillary electrical components and circuit boards on the watercraft. Schematic Design Calculations 243904 There were many design considerations when selecting the 2N3904 transistor. In this application the transistor was being used to toggle to the slave select lines on the two PIC microcontrollers. The signal from the XBee board was first put through the LM399 comparator so the input was at 0 and 5 volts. From the specifications for this component the collector emitter voltage could be as high as 40V while the emitter base voltage could be as high as 6 volts. In this application neither of these two voltages would be much above 5 volts nominal. The next calculation was to consider using this component as a switch, which is dependant on the ration of collector-emitter current to base-emitter current. Ideally, when using this component as a switch the ration would be between 10 and 20. The following equations were use used for finalizing on this component: Ratio I BE I CE I BE VB VBE RB I CE VC VCE RC VB VC 5Volts VBE 0.95V VCE 0.3V RB 27 K RC 4.7 K Ratio 6.667 Power ( I BE * VBE ) ( I CE * VCE ) Power 0.000995W As can be seen from the design calculations the ratio is a little lower than desired. However, there were no problems with the component in this application as verified with voltage measurements so the resistance values were not changed. The power dissipation of less than 1 milliwatt is well below the rated value of 625 milliwatts. LM324 The LM324 was used to source current for the display LEDs on the watercraft. The component can source up to 40mA of current which is well below the current that was to be drawn by the LEDs. Not shown on the schematic diagram are the 300 Ohm resistors used to limit the current to the LEDs which would guarantee they are drawing less than 40mA. Headers The headers available in the TA area are rated up to 4amps. Dip Sockets The Dip sockets house the PICs and the LM324. They will not be seeing currents greater than 20mA which is well within their rated specifications. 300 Ohm Resistor This is a current limiting resistor on the iButton LED. The voltage drop across the LED was assumed to be around 2 volts leaving 3 volts to be dropped across the resistor. The following calculations were made: Vs VLED R Vs 5Volts I LED VLED 2Volts R 300 I LED 10mA Presistor V * I 3 * 0.01 0.03W XBee Additions Description The XBee Additions are the additional components that were added to the XBee boards which were issued at the beginning of the project. Schematic Design Calculations Headers The headers available in the TA area are rated up to 4amps. 5K Pull Up Resistor for iButton Specified in the iButton documentation. LM339 This component was selected to act as a level shifter. The intention was to shift the 3.3V signal from the XBee pic to 5 volts for the PICs on the Communications Board. The nice teaching assistant recommended that we use this approach as the level shifter provided on the XBee boards were slow and susceptible to noise. The LM339 is the comparator of choice in the ME218C series so it was implemented into the watercraft and its addition seemed to resolve the issues that were being seen when using the XBee level shifters. 10K Resistors for Voltage Divider into LM339 Voltage divider to set comparator voltage value. 10K Ohm is within range of values that is typically used in this type of application. 3.3K Pull up resistors for output of LM339 Recommended “rule of thumb” value for use as a pull up resistor on an open collector component. Helm Power Board Description The purpose of this circuit board was to provide the following power outputs from one rechargeable NiCad Battery pack, supplying a nominal voltage of 7.2V: Power Level Destination 7.2 Volts E128 Microcontroller 5 Volts Communication Boards 1 and 2, Ship Number Display Board Schematic Design Calculations LM7805 This component is rated to supply up to 1 Amp of current and will take an input voltage of up to 20 Volts. A conservative estimate for the amount of current being drawn by the 5 volt components on the helm are: I total I ComBoard1 I ComBoard2 I ShipNumberDisplayBoard I IndicatorLED I IndicatorLED Vs VLED 5Volts 2Volts 0.01A RLED 300 I ComBoard1 I iButtonLED I iButton I 74 HC14 I MM 74 HC 244N I Encoders I LEDs I ComBoard2 I LM 324 ITapeSensor I ShipNumberDisplayBoard (2 * I MM 74 HC 244N ) (2 * I SN 74 HC 595N ) (2 * I 7 segmentLEDdisplays) I iButtonLED I iButton Vs VLED 5V 2V 0.01A RLED 300 Vs 5V 0.001A R pullup 5 K I 74 HC14 0.000020 A I MM 74 HC 244N 0.000080 A I LEDs 5 * Vs VLED 0.05 A RLED I Encoder 0.040 A I LM 324 0.001A ITapeSensor I Emitter I det ector 0.00060 A Vs VLED 0.00660 A RLED I SN 74 HC 595N 0.000080 A I 7 SegmenLEDDisplay 7 * Vs VLED 5V 2V 7* 0.07 A RLED 300 I total 260mA This is a very conservative estimate because it assumes that all the LEDs will be on at one time. Even so, the expected worse case current draw is much less than the 1 amp the LM7805 is capable of supplying. IRLZ34N For this application the following equations was used for calculating the drain current: I drain I E128 XBee I total( above) I E128 XBee 250mA I total( above) 260mA I drain 510mA As can be seen from this calculation the IRLZ34N is a suitable component for the amount of current (which is rated up to 21 amps) Headers The headers available in the TA area are rated up to 4amps. Battery Life Calculation It was required that a calculation of battery life was completed. The selected battery was a Tower Hobbies 1500 Ultra Sport with a nominal voltage of 7.2Volts and a capacity of 1500mAh. The requirement was that the battery be able to last at least 8 hours. For this calculation the current draw from above may be used as a starting spot but it is assumed that this maximum current draw will be done for very short durations (5 minute games, conservative 6 games). This means that the full 510mA will be drawn for only ½ hour of the eight total hours. For the rest of the time the system will be in a much less taxing mode where: LEDs will be off and not drawing any current (minus 200mA) XBee board will be in a lower power state (minus 50mA) Encoders will not be drawing any current (minus 40mA) E128 will be working in a minimal state (assume that in the nonuse state current draw is cut in half) This reduces the current draw to around 150mA. The following equations were used to verify the system would stay on for eight hours: mAhmax mAhuse mAhs tan d _ bye 1 mAhuse 510mA * hour 255mAh 2 mAhs tan d _ bye 150mA * life life mAhmax mAhuse 1500mAh 255mAh 8.3hours 150mA 150mA Since there was a considerable amount of assumptions made to come to this value the helm was left on overnight to verify. Communications Board 1 Description The purpose of the Communications Board 1 was to provide input / output connections for the following inputs and outputs that were associated with the 24 pin connector on the E128: Encoders – Interrupt driven iButton LED display (non ship numbers) Communication with the XBee Pic for Okay to Send and Message Waiting Binary, button inputs o Throttle – interrupt driven o Throttle direction o Special 1 and Special 2 Schematic Design Calculations Encoders – Interrupt driven The encoders are a stand alone, two channel encoder unit that is power with 5 volts. Before integration with the system was completed the unit was measured using and oscilloscope to ensure the voltage level outputs were correct. iButton A 5K Ohm pull up resistor was used on the data line per the iButton reading specifications. The iButton LED, a purely cosmetic, no functional LED, was powered with 5 volts and a 300 Ohm current limiting resistor. LED display (non ship numbers) The LEDs were powered with an MM74HC244N buffer IC. They were wired in series with a 300 Ohm current limiting resistor. See the design calculations / considerations for the 244 in the Ship Number Display Board section. Communication with the XBee Pic for Okay to Send and Message Waiting This was a data line only and did not require any special considerations. The only issue was that the signal from the XBee was a 3.3 Volt signal and the E128 was at 5 volts. From the specifications for the E128 it was found that a voltage level over 3 would register as a high so it was thought that the signal would not need to be level shifted. After some initial testing the assumptions were proven true. Throttle, Special 1 and Special 2 Buttons These buttons were all push type buttons that needed some form of debouncing. Instead of trying to accomplish the debouncing in software it was decided to do it with hardware. Using one 74HC14 inverter, a resistor and a capacitor it was possible to debounce the signal to an acceptable level. The circuit used was the same switch debouncing circuit that our group had used in the other two projects, as well as the same circuit that was presented in class. Because of the previous experience, and the trusted source of information, the circuit was used with no additional design considerations. Communications Board 2 Description The purpose of the Communications Board 2 was to provide input / output connections for the following inputs and outputs that were associated with the 20 pin connector on the E128: Tape Sensor (analog water delivery input) Outputs to the ship number display board Output to two additional display LEDs (note, these were not actually used in the final helm) Schematic Design Calculations The only component that had design considerations on this board was the tape sensor. Tape Sensor For the Tape Sensor input an LM324 was used to amplify the signal for reading by the E128. Per the instructions given last quarter a virtual ground of 2.5 volts was created using on of the 4 op amps on the LM324 and a simple voltage divider of two 10K Ohm resistors. The gain resistor for the detector half of the tape sensor and the current limiting resistor for the emitter portion of the tape sensor were dialed in empirically to achieve the proper performance from the water delivery button. Ship Number Display Board Description The Ship Number Display Board was built to drive the 2 digit 7 segment LED displays for showing the Craft Number currently linked to the helm. The seven segment LEDs require a considerable amount of overhead to make them work so the circuitry was moved to its own circuit board. Schematic Design Calculations The main design considerations for this board were the interactions between components. MM74HC244N The main consideration for the MM74HC244N was making sure the unit could provide enough current to drive the LEDs. The LEDs had a current limiting resistor in series to keep the current for each LED at 10 milliamps. Each pin on the 244 can source or sink up to 35 milliamps. In the intended application they will actually be in a sinking configuration. When sourcing on seven different pins the power dissipation in the 244 becomes an issue. The power dissipation is rated at 600mW. The following equation was used to figure out the power: P 7 *V * I V 5V I 0.01A P 0.35 A 350mW SN74HC595N The main consideration with the shift registers is ensuring that they will be able to turn to the LED buffers (the 244) on and off. The ability to meet the requirement is dependant on the amount of current that the shift register outputs can source and sink. From the spec sheet the 595 can source or sink up to 35 milliamps per pin. From the spec sheet for the 244 the maximum current on the input pin is +/- 1 microamp.