1 Introduction - Chipping Sodbury Greenpower
Contents
1. There are some example programs on the support website at http www greenpower beamweb co uk groups electronics GpSpeed index html 8 More Information There is more information on the CSS s Electronics website at http www greenpower beamweb co uk groups electronics 9 Copyright and Warranty The design is copyrighted to the Chipping Sodbury Rotary Racer Greenpower team It is provided free for non commercial educational uses Note we do not provide any warranty that these systems will work or guarantee any support The design information software and any kits are supplied on an as is basis 10 Notes 1 The board has a hardware current limit feature When this triggers it switches of the output power until a new PWM pulse arrives If the power is set to 100 this will not happen Easing off the power and then bringing it back up will restart the output If this happens the value of resistor R18 can be reduced in value to raise the over current tripping point Normally the software would limit the current before this point is reached 2 Always get an adult to check over the software and test it before using it in a Greenpower Car 3 Make sure the software is fail safe If the throttle is shut off the motor should be shut off no matter what 4 When using electronics software to control the motor in a Greenpower car Always have a physical main power switch easily accessible to and known to the driver in case2. I2C bus data line for displays or other devices C 0 User 0 I2c Int General user line on display connector B 3 User 1 General user line on display connector C 6 SER1 TX P3 serial port hardware uart 7 SER1 RX P3 serial port hardware uart A 5 SER2 TX P5 serial port software uart A 4 SER2 RX P5 serial port software uart Each of these pins can be configured as a digital input or digital output while some may also be used as analogue inputs As well as manually in software reading values from and driving these pins some can be used by on chip hardware peripherals The peripherals provided include Peripheral Pins Description PWM C 1 Hardware PWM signal generator PWM C 2 Hardware PWM signal generator ADC Analogue pins Hardware analogue to digital converter 8 or 10 bits UART C 6 C 7 Hardware UART for serial communications 12C C 3 C 4 Hardware 12C bus master or slave It is best to use these hardware peripherals as much as possible to simplify programming 7 1 Notes on programming The PIC processor is essentially an 8bit microprocessor that is it natively works with 8bit numbers either signed numbers in the range 128 to 127 or unsigned numbers in the range 0 to 255 The software development systems provide support for 16bit numbers 32768 to 32767 or O to 65535 and indeed 32 bit numbers for C by adding code to perform the appropriate mathematical operations but this is slowe
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4. AXE033 or used for other purposes If the I2C bus is not required the lines can be used as digital IO lines for driving LED s or switch inputs 4 4 Controller Connector P4 This is a simple 8x2 0 1 inch header This is used to connect to an external control and or data logging module using 16way IDC connector Either a cable or a small PCB can be mounted here Pin 1 has a dot on the PCB Name Connector Processor Pin Description Pin 24V P4 2 24V input after filtering For battery voltage measurement or limited power supply lt 200mA 12V P4 4 12V regulated power supply Max 500mA 5V P4 6 5V regulated power supply Max 100mA Current P4 8 RA3 Hall effect current sensor output 2 5V 2Volts MotorPwm P4 10 RC2 Motor PWM input or output if gpSpeed drives this FanPwm P4 12 RC1 Fan PWM input or output if gpSpeed drives this I2C_CLK P4 14 RC3 I2C bus data or for general digital IO usage I2C_DAT P4 16 RC4 I2C bus clock or for general digital IO usage Gnd Odd pins All odd pins are ground With the gpSpeed processor removed or software configured not to drive the PWM signals a remote module can use the gpSpeed board can a simple MOSFET output stage Alternatively the gpSpeed processor can drive the motors and fans and take commands over the I2C bus from a remote controller 4 5 Serial Programming Connector P5 This is a simple PicAxe compatible serial progr
5. Greenpower Speed Controller GpSpeed Development Manual Chipping Sodbury School Rotary Racer V1 1 2015 11 21 T Barnaby Preliminary Table of Contents TTT OCU CEU Wiysan doe ceptcercenesxssnsessastessatace EA EE E EE EE E E E A Na E 2 A O e a ais A Alomar 2 3 F llkSystem US ias 4 AKOE EOI T Si T EAEE E AE EEE 6 4 1 Power Connectors P12 Pd Bai did REE E E OR TE AAEE 6 4 22 Input Signal Connector Pl RA 7 4 3 Display Connector Peasy ds 7 AAs Controller Connector PA o Ec paras 7 4 5 Serial Programming Connector Pod adan 8 4 x Ve Weal Connector Pos ld 8 4 7 PIC Programming Debug Connector PG ccecceesecesecesseceeeessecesecesneceseceeeeceseeeseeceaeeceesaeeseseaeees 9 Be COMME CHINE CINE Sa oi 9 Oi Programming erro a a a aii 11 6 1 Notes on prorrata iiaiai iaren eiia 12 6 2 Programming using the PicAxe environ Met ooccoonoonnonncnnnccoronoccononnsonoornoon crono nonna renos nono prono nooo ros 12 a AA ON 13 A O AE E 13 8 COPE and WV AE AREY on a ias 13 NOS AN AR A ays i 13 4 Z q Y 4 A 1 Introduction This document is an extension of the GpSpeed User Manual that gives a more detailed description of the GpSpeed Greenpower motor speed controller developed for the Greenpower Cars It describes all of the connector pins and gives some information on developing software for the board The idea is to provide a platform allowing teams to get pupils involved in electronics and software rathe
6. amming and debug connection Requires use of a PicAxe serial download cable with a 3 5mm jack plug Name Connector Processor Pin Description Pin SER2_TX P5 1 RAS Serial TX outside SER2_RX P5 2 RA4 Serial RX middle Gnd P5 3 Ground tip 4 6 Serial Connector P3 This is a simple set of 0 1inch spaced header pins A simple Molex 4 pin connector could be used This is a simple serial connector connected to the PIC s hardware UART pins Could be used for programming external serial modules or general digital IO usage Pin 1 has a dot on the PCB Name Connector Processor Pin Description Pin Gnd P3 1 Ground SER1_RX P3 2 RC7 Serial RX SER1_TX P3 3 RC6 Serial TX 5V P3 4 5V power supply 4 7 PIC Programming Debug Connector P6 This is a standard PIC 6 pin programming port It can be used for development in C using standard PIC development tools Requires a suitable PIC 6 x 0 1inch programming lead Pin 1 has a dot on the PCB Name Connector Processor Pin Description Pin RESET P6 1 MCLR Microprocessor reset line 5V P6 2 5V power supply Gnd P6 3 Ground ICSPDAT P6 4 RB7 Programmer data ICSPCLK P6 5 RB6 Programmer clock NC P6 6 Could be used as general digital IO if PIC programming is not needed and CPU set to allow use of the lines 5 Connecting Things Most of the user inputs are fed through a simple passiv
7. ata log memory 6 Adding a Display The GpSpeed controller has a connector that is designed to be used to connect to a driver display This RJ12 type of connector provides a simple 6 wire interface This provides 5V power an I2C serial bus for communications and two spare lines for other uses such as switches or LED s It can easily be used with the Picaxe AXE033 module Module http www picaxe com Hardware Add on Modules Serial LCD Module Datasheet http www picaxe com docs axe033 pdf The display can be used to display various information from the GpSpeed controller Some examples are Motor current The instantaneous motor current Average motor current over a period of time ideally the last lap Battery voltage Speed Motor temperature Throttle position The Picaxe AXE033 module comes as a simple kit to build It also offers the ability to install a real time clock chip and battery to maintain the date and time for data logging or other purposes When making the AXE033 module note the following 1 The J1 link needs to be installed for I2C mode 2 The link J1 should be left open 3 Make sure you solder the LCD PCB to the controller PCB the right way around To wire the LCD module to the GpSpeed an RJ12 telephone type of lead can be used RS 446 664 The GpSpeed connector information for display connector p1 gives the pinout and the colours of the wires in a typical RJ12 lead Some Notes 1 Try and keep
8. ded depending on the usage desired By installing extra components and changing the on board software the design can be extended to perform many different functions We provide basic software that will operate the system It is for teams to extend this system as wanted and to get involved in the electronics and software design So what can it do Can act as simple soft start device Connected in line with the motor can simply provide a motor soft start on power on while using conventional switched relay systems Can act as a simple soft start device with power switch Using a simple on off button will essentially behave as a soft start relay Can act as a simple speed controller with throttle A simple potentiometer either twist grip or other can be used to control the speed Power limiting can be performed with an additional potentiometer to eek out those battery ampere hours Can display information to the driver and have driver buttons via a separate display module Can act as a PWM motor speed MOSFET output stage battery voltage and current measurement device for a higher level computer control module no processor installed Some Features Uses mainly through hole components allowing easy assembly by pupils Relatively low cost probably about 70 VAT Uses screw terminals for the main wire connections so easy to integrate by pupils Has reliable high current PWM MOSFET output stage 160 Amps with hardware and software c
9. e reading is 6 7317 5 1023 0 0329 In fixed point arithmetic scaled by 100 the scaling would be 3 29 which could be roughly implemented as 10 adc 3 in integer arithmetic e Current We have used a hall effect sensor to measure the current The one we have used is a HXS50 RS part number 532 9126 This uses 5Volts and provides a voltage of 2 5V with no current On increasing current the voltage will decrease It is configured with a 2 turn primary for a 0 to 75A mp range Thus its output voltage with respect to current will be scaled by 0 625 25 0 025 The ADC s in 10bit mode provide values of 0 1023 for a 0 to 5V input First the ADC s output needs to be inverted due to the inverse current This can be done by subtracting the value from 512 The software scaling to provide a true current reading is 5 0 025 1023 0 1955 For fixed point arithmetic scaled by 100 the scaling would be 19 55 which could be implemented as 119 adc 6 e Temperature A temperature sensor such as a TMP37FT9Z or TMP36GT9Z that provides an analogue voltage can be directly connected to one of the analogue inputs With the TMP37FT9Z it provides a voltage of 20 mV C TMP36 is 10 mV C So the software scaling factor for a TMP37 would be 5 0 02 1023 0 244 This can be implemented in 100 scaled integer arithmetic as t 24 adc For a TMP36 would be 5 0 01 1023 0 488 This can be implemented in 100 scaled integer ar
10. e signal conditioning circuit This consists of a simple resistor voltage divider R1 and R2 followed by a capacitor C1 to filler the incoming signal and remove spikes By default the inputs have R1 4K7 R2 100K and C1 1uF This gives a near 0 5V input range with a degree of low pass filtering The battery voltage input has suitable on board resistors to handle a 0 to 33 6 Volt range 47k 8 2k If it is desired to use any of these pins as outputs the capacitor should be removed and the value of the input resistor R1 lowered to about 100 Ohms giving some degree of protection to the processors I O pin Inpud input Te FIC Irci Te FIC Irci OY Ground GV Ground If lower voltage level inputs are needed an external operational amplifier circuit can be used that can scale and offset the voltage as required R5 R6 and R6 can be adjusted for voltage offset and gain The input terminal blocks have OV and 5V connections available to allow two and three wire sensors to be easily connected See the Circuit Diagram for more details e Voltage Assuming the GpSpeed unit is connected to the batteries then it can directly measure the battery voltage without any additional wiring The resistor dividers have by default a 47k and an 8 2k resistor So the input voltage is divided by 47000 8200 8200 6 7317 The ADC s in 10bit mode provide values of 0 1023 for a 0 to 5V input Thus the software scaling to provide a true voltag
11. elemetry etc etc Can use it as a battery testing switch and datalogger to a PC With a suitable load bank multiple 50W bulbs attached the unit can perform a discharge cycle sending voltage current info to a PC laptop and then switch off the load automatically when down to 11Volts Info on our control data logger project is at http www greenpower beamweb co uk groups electronics gpControl index html If you use this system all I ask is for you to involve the pupils as much as possible in the design build development and usage of the systems produced The idea is to show educate and try to inspire young engineers 3 Full System Usage This diagram shows a possible full usage scenario for the GpSpeed controller board 4 Connections P12 P13 Power Connector Reset Switch P6 IDE Connector P4 Controller Connector P3 Serial Port P2 Input Connector P5 Picaxe P1 Display Connector Programming Connector The connections are 4 1 Power Connectors P12 P13 These are large screw terminal connectors allowing wire of up to 16mm 2 to be connected We recommend the use of 10mm 2 wire The PCB is marked with B B M M and F Be very careful in making sure these connections are correct Name Connector Pin Processor Pin Description F P12 1 Fan drive negative output Switched PWM through LC filter to provide a DC voltage Connect FAN s between
12. hen use the PicAxe Basic language like programming environment to develop software for the GpSpeed system The PicAxe serial download cable must be used to download the program to the CPU on the board PicAxe 28x2 CPU http www picaxe com Hardware PICA XE Chips PICA XE 28X2 microcontroller PicAxe download cable http www picaxe com Hardware Cables PICA XE USB Download Cable PicAxe development http www picaxe com Software PICAXE PICA XE Editor 6 software MS Windows PicAxe development http www picaxe com Software PICA XE A XEpad software Linux Note the Picaxe MSWindows editor will run under wine on Linux as well There are some example programs on the support website at http www greenpower beamweb co uk groups electronics GpSpeed index html 7 3 Programming in C There are a few C development environments you can use There is the Microchip MPLAB the L inux pikdev and a simple Linux sdcc based system amongst others You will need a USB ICSP download cable 6pin to download the programs to the board Alternatively with an appropriate bootloader programmed into PIC chip a PicAxe download cable can be used Digilent Chipkit http uk farnell com digilent chipkit pgm programmer tdgl015 chipkit programmer Low cost pgm dp 2285430 programmer Pickit2 USB programmer http uk farnell com microchip pg164120 programmer pickit 2 full PIC standard programmer _ speed dp 9847170 Ntt 9847170
13. ithmetic as t 49 adc e Speed The speed can be input from a basic reed hall effect or optical switch driven by a magnet on a wheel like a cycle computers sensor A reed switch can be connected between the input and the 5V line The software would accurately time the period between pulses From this it then calculate the distance and the speed of the car e Throttle The throttle input can be a simple resistive potentiometer or a hall effect device The system provides a OV and 5V connections for this With a resistive potentiometer the ADC will provide a value between 0 and 1023 With a Hall effect input they commonly provide a voltage between 1 and 4V so the range of ADC values would be in the range 204 819 e Display and Switches A display and switches can be connected to the RJ12 connector This provides 5V power ground an I2C serial interface and 2 I O lines A Picaxe AXE033 LCD panel set to 12C mode can be used for a display The User IO lines can be used for switches or LED s e Serial Interfaces The SER1 and SER2 serial interfaces can be used for telemetry GPS or other devices e Real time clock If a PicAxe Serial LCD module AXE033 is used then it can be fitted with a real time clock chip DS1307 to maintain a battery backed up date and time This would be accessible over the I2C bus Alternatively a simple module could be made to interface with the controllers P4 connector that can have an I2C RTC chip and perhaps some d
14. r than native 8bit operations The PicAxe Basic environment only supports unsigned integer values in 8 bit or 16 bit forms The C compiler can also generate the code to perform 32bit floating point calculations but this results in large and slow code and so is generally best avoided So it is generally best to work in low bit count integer arithmetic To achieve a reasonable accuracy it is useful to use fixed point arithmetic with 16bit values For example to store 20 12 Volts you could store and manipulate the number 2012 ie the number is scaled by 100 to effectively give two decimal points of accuracy When working with low bit count integer arithmetic you have to be very careful of over and underflows in calculations So for each calculation you write you should consider what the minimum and maximum values are and if necessary pre scale them before performing the calculation Note that the mathematical divide operation is the most difficult for a processor to do and should be avoided where possible Sometimes a multiplication with fixed point numbers Or appropriate scaling can be performed on others Also the processor is good at multiplying dividing by factors of 2 such as 2 4 8 etc Most of our examples scale the voltage current temperature and other readings by 100 to get two decimal points of resolution using integer arithmetic 7 2 Programming using the PicAxe environment The GpSpeed board can use the PicAxe 28x2 CPU chip and t
15. r than provide a fully featured built end system The basic speed controller can be extended with software and or other hardware modules to provide a highly featured electronics control system for a Greenpower car As well a speed control it offers battery voltage current and other parameter monitoring 2 Overview A basic electronic speed controller for Greenpower Electric cars We have been using a team built motor speed controller in the Rotary Racer cars for a number of years 3 different designs have been built and used This is a new design that tries to bring all of our ideas together to produce a relatively simple pupil build able speed controller which is flexible enough for Greenpower teams to use and allow for different uses as well as provide extendibility The idea is to provide a platform and possibly a kit allowing teams to get pupils involved in electronics rather than provide a fully featured built end system The basic speed controller can be extended with software and or other hardware modules to provide a highly featured electronics control system for a Greenpower car As well a speed control it offers battery voltage current and other parameter monitoring We provide an electronic schematic circuit diagram and PCB layout in Kicad format This allows modifications by teams if desired We will probably also supply manufactured PCB s allowing teams to easily build the design given here Not all of the components are nee
16. the cable as short as possible 2 Run the cable away from battery and motor power cables and any others that could cause interference 3 Note that the displays control variable resistor may need to be adjusted in order to actually see the display 4 Itis worth adding 2k2 pull up resistors from the I2cClk and I2cDat lines to the 5V power line at the display end of the cable to reduce the effects of noise The display can be written to using normal Picaxe AXE033 I2C commands See the AXE033 datasheet and the GpSpeed demo programs gpspeed test display bas and gpspeed demo 0v1 bas for more information 7 Programming The following table shows the processor pins from a software perspective Pin Description B 1 LED C 2 Motor PWM This drives the main motor power MOSFET s via the MOSFET driver chip C 1 Fan PWM This drives the FAN MOSFET The output of this is via an LC filter network to provide a variable DC voltage for fan control A 0 Analogue Input 0 10 throttle 0 to 5V A l Analogue Input 1 I1 misc 0 to 5V A 2 Analogue Input 2 Battery Voltage measurement A 3 Analogue Input 3 Motor Current measurement Hall effect B 4 Analogue Digital Input 12 0 5V B 2 Analogue Input 8 Current measurement Raw B 0 Error error from Motor PWM Pulled low on MOSFET over current C 3 I2C Clk I2C bus clock line for displays or other devices C 4 2c DAT
17. this and M B P12 2 Main battery positive input Should be fused at 70 Amps B P12 3 Main battery negative input and chassis ground M P13 1 Motor positive output 24V DC for motor fan and other items The Hall effect device will measure current taken through this terminal M P13 2 Motor negative output Switched PWM 4 2 Input Signal Connector P2 This is a small screw terminal connector for control inputs Pin 1 has a dot on the PCB Name Connector Pin Processor Pin Description 2 P2 1 RB4 General digital or analogue input 0 5V 5V P2 2 5V supply Gnd P2 3 Ground I1 P2 4 RA1 General analogue or digital input 0 5V 5V P2 5 5V supply Gnd P2 6 Ground I0 P2 7 RAO Throttle input analogue 0 5V 5V P2 8 5V supply 4 3 Display Connector P1 This is an RJ12 plug in connector Either an RJ12 telephone type of lead or a twisted pair CATS networking type wire can be used Name Connector Processor Pin Description Pin I2C_INT P1 1 RCO Used as an 12C bus interrupt or for general digital IO usage Blue Gnd P1 2 Ground Yellow I2C_DAT P1 3 RC4 I2C bus data or for general digital IO usage Green 5V P1 4 5V supply Red I2C_CLK P1 5 RC3 I2C bus clock or for general digital IO usage Black User1 P1 6 RB3 General digital IO usage White This presents an I2C bus that can be connected to a simple LCD display module such as the PicAxe
18. urrent limiting proved over 5 years of GP racing Filtered efficient and reliable 12V and 5V supply for electronics from the main 24V battery supply Used on board and available to external electronics Has a simple PIC processor that can be programmed using Picaxe Basic or C to do various tasks Simple speed controller software and examples provided in Picaxe Basic and C Has onboard battery voltage and hall effect motor current measuring ability This can be used for display to the driver or other purposes Has 24V PWM fan driver with filter to control variable speed motor cooling fans or other devices Three external analogue or digital inputs One for throttle on off and two free for use temperature car speed Has I2C bus connection for driver display panel controls A simple LCD or LED display module such as PicAxeAXE033 or own designed board to show the user voltage current speed etc Has limited memory for data logging An I2C memory device could be connected to extend this but there is no real time clock Both could be added via Control connector Has a serial port with power connector to allow a basic telemetry module to be attached Has connection to a separate car computer board for higher level control This can be connected to RR s existing PIC based computer to a new ARM based data logging computer module we are developing or to a Raspberry Pi etc These will allow higher level control including data logging t
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