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By Robert Priestley Part 2: Building It! Last month we introduced our new OzTrip Car Computer – arguably the best car computer ever published. In this final part, we’ll look at some of the other features and then move onto construction, installation and calibration. As we mentioned last month, the OzTrip Computer can most easily be used in cars with standard electronic fuel injection (EFI) systems. The computer uses data already available within the EFI system. With modifications (involving the use of an optional PC board) it can also be used in vehicles with carburettors or non-standard EFI. This entails the fitting of a fuel flow sensor – not a difficult job at all. EFI operation The OzTrip Computer measures the fuel flow of an EFI engine by measur- The OzTrip Car Computer is easy to build, easy to fit and easy to calibrate. The best part: you save money! 64  Silicon Chip ing the time one injector is open. The main components of the fuel delivery system in an EFI engine include the fuel pump, pressure regulator, fuel rail and fuel injector valve. The fuel injectors are under the control of the engine management computer (EMC). This adjusts the time the injector is open and therefore the amount of fuel sprayed into the cylinders, according to the speed of the engine and the load on it, attempting to achieve maximum efficiency at all times. The pressure in the fuel rail, which feeds the injectors, is kept constant by the pressure regulator. Because of this, the fuel flow through each injector can be assumed to be the same (on average) so we only need to measure one injector to determine the total fuel flow. The fuel flow is directly proportional to the injector open time and by measuring the injector open time we can calculate the fuel consumption. Before we can determine fuel flow, the computer needs to be calibrated so it can relate fuel consumption to injector open time. This is achieved by measuring the total injector open time over a full tank of fuel, then entering the total fuel used during the calibration process into the computer. The computer has a special calibration mode which makes This photo of an early prototype shows the back-to-back method of construction. The microcontroller used in this shot was actually a reprogrammable type to assist in development, as distinct from the one-time programmable chip finally used. Some resistor values may also be slightly different – use the component overlays for construction! this easy to do. Calibration can be performed over several days if required. The greater the volume of fuel used during calibration the more accurate the calibration process is. The 68HC705C8A microcontroller has a timer input pin which is used to measure the pulse width of the injector signal. The computer’s fuel input can be directly connected to the injector. The injector has two connections: one side of the injector coil is connected to +12V DC and the other to the engine management computer (EMC). The OzTrip Computer must be connected to the EMC side of the injector. It is sometimes easier to make the injector connection directly across the vehicle’s EMC, which is usually located in the front passenger foot well or under the dashboard. Note that this method of fuel measurement is only suitable for EFI engines with one injector per cylinder and constant fuel rail regulation. Other engine setups may have to be treated as a carburetted engine and a fuel flow sensor fitted. terminals of the fuel sensor is connected to the input terminals via shielded cable – the shield itself connects to the “ground” terminal. There are various types of fuel flow sensors (or meters) available but the flow sensor used by Oztechnics produces 780 pulses for every 100ml of fuel which flows through it. This is its calibration number. The OzTrip Computer needs the calibration number entered into it (via the Fuel Calibration menu) so it can calculate the fuel flow. The flow sensor should be mounted in a vertical position with the fuel entering at the bottom of the sensor and leaving at the top for optimum operation. Diagnostic/calibration menus In addition to the 81 functions which can be selected, two-sub menus are available for Diagnostic and Calibration functions. When the diagnostic menu is accessed with the UP + Set/Clear key Speed alarm The speed alarm has a piezo siren and a visual “SLO” message to warn you that you are exceeding the speed limit. The alarm sounds 5km/h above the set speed – for example, if you set the alarm at 60km/h, it will trigger when your speed reaches 65km/h. The speed alarm can be set and cleared when the “speed” is displayed, using functions 1, 28 or 55. Pressing the SET/CLEAR key when the speed is above 40km/h will set the speed alarm at the current speed. To disable the speed alarm the SET/ CLEAR key is pressed when the speed is below 40kmn/h. Sprint timer Flow sensor operation Fitting a fuel flow sensor for non-EFI or non-standard EFI vehicles is quite simple: the fuel line is broken somewhere between the fuel pump and the carburettor and the fuel sensor is connected in series, securely clamped to the line by worm-drive hose clamps. Connection to the OzTrip computer is via optional PC board 3. Each of the sequence a “diAg” message is briefly displayed then the ENTER LED lights. You must enter a value between 1-5 into the computer to select the appropriate diagnostic function. The Diagnostic functions are listed in Table 4. When the calibration menu is accessed with the Down + Set/Clear key sequence a “CAL” message is briefly displayed then the ENTER LED lights. You must enter a value between 1-7 into the computer to select the appropriate calibration function. The Calibration functions are listed in Table 3. This fuel flow sensor is available from Oztechnics for those with carburetted or non-standard EFI vehicles. The sprint timer is used to calculate the time it takes for the vehicle to travel over a preset distance. Typically this distance would be 400m (roughly the old “quarter mile”) because that is the usual distance drag races cover. But if you want to time your vehicle over any distance – 100m or 100km, all you have to do is tell the computer. When the Sprint Timer option is selected from the Cal Menu/Option 7, April 2000  65 This photo and the diagram show the assembly details for board 1 (the display board). The connections all go to PC board 2, with links A-H actually 1kΩ resistors. All other connections are short wire links. Note the 10mm spacer position on the PC board. the computer asks for the distance to be timed (“Dist”) and then a 9-second countdown starts. When the count down reaches 0000, a BEEP is heard and the timer starts. When the vehicle has travelled the entered distance the timer is frozen, displaying the time duration with an accuracy of tenths of a second. Pressing the Mode/Enter Key returns the computer to normal operation. Journey counter The Journey counter is the main distance/timer counter and is represented by the Trip 1 Counter, F5 (distance) & F20 (time). The functions which are derived from the Journey counter are F2, F9, F11, F13, F15, F18 & F21. Parts List 2 PC boards, each 135 x 31mm, coded QIP1 & QIP2 1 4MHz crystal 4 PCB pushbutton switches (S1 -S4) 1 case 1 red acrylic (filter) front panel 1 10mm spacer 2 screws Semiconductors 1 68HC705C8A programmed microcontroller (IC4) 1 40106 quad Schmitt trigger inverter (IC3) 1 LM317 variable regulator (REG1/IC1) 1 LM78L05 5V positive regulator (REG2/IC2) 20 BC559 PNP transistors (Q1Q20) 1 BC547 NPN transistor (Q21) 3 1N914 diodes (D3, D4, D6) 3 1N4004 diodes (D1, D2, D5) 66  Silicon Chip 3 1N4733 5V zener diodes (ZD1ZD3) 4 FND506 7-segment LED displays (SEG1-SEG4) 8 3mm red LEDs (LED1-LED8) Capacitors 1 1000µF (C7) 2 100µF (C10, C12) 1 10µF (C11) 6 0.1µF (C5, C6, C8, C9, C13, C14) 2 .001µF (C1, C2) 2 22pF (C3, C4) Resistors (1%, 0.25W) 1 10MΩ (R5) 2 33kΩ (R1, R3) 9 10kΩ (R2, R4, R9, R11-R13, R33-R36) 23 2.2kΩ (R8, R14-R25, R37-R44, R58-R59) 10 1kΩ (R6, R7, R60-R67) 8 22Ω (R26-R32, R45) When the computer is RESET using the Mode/Enter + Set/Clear combinations, the Distance Travelled on the Trip1 counter is copied to the Distance Remaining Function (F6) and the Trip1 counters are cleared ready for a new journey. If the same trip is being travelled then the distance remaining in F6 is already set, otherwise it will have to be entered for correct operation. If the distance remaining of journey is not entered or is incorrect then the distance remaining of journey (F6) & Time remaining at current/average speed to complete journey (F23/F24) will be incorrect. That completes the description of the various functions of the OzTrip Computer. Now we’ll put it together! You may need to refer to the circuit diagram published last month if any of the following is unclear. There are some differences in the way components are marked on the PC board and in the text. For example, we refer to transistors as “Q1, Q2,” etc but the PC board shows them as “TR1, TR2,” etc. Likewise regulators REG1 and REG2 are labelled “IC1” and “IC2”, the 7-segment displays DISP1-4 are labelled “SEG1-4”, the LEDs are labelled “L” and some capacitors shown in µF on the circuit may be shown in nF. Construction There are two PC boards to assemble. This is made easy by following the component mask printed onto the PCBs. Here are the assembly details for PC board 2. The RED leads go to PC board 1, while the GREEN leads go to PC board 3 if it is used. The parts shown in red are installed first, on the reverse side of the PC board. IC5, R58 & R59 (shown in blue) are optional and not included in the kit. Note also that some of the parts adjacent to IC3 on the prototype are not used in the final version. Before mounting any components, check that the PC boards fit into the case and the case closes properly. It may be necessary to round the corners of the boards slightly with a file to en-sure the cases halves fits together. Start with PC board 1, the display board. This is the easier of the two main boards because all components are mounted on one side. Solder in the lowest profile components first (resistors), followed by the LEDs and transistors, taking care with the polarity of the LEDs (in all cases, the anodes or longer legs go to the right). The LEDs should all mount so that they are about 3mm above the PC board. The transistors mount hard down on the board. Next solder in the four LED displays – the decimal points all go to the bottom – and the four pushbutton switches or keys. Again, these must be inserted the right way for switching action to occur – the notches go to the top and bottom. The LED displays and switches mount right down on the PC board. Note that there are four diode positions marked on the PC board which are not used. PC board 2, the one containing the ICs, has components mounted on both sides. You must solder the components on the bottom side first as IC1 hides resistors R26, R37-R44 and transistors Q13-Q20, which are mounted directly under it. Resistors R37-R44 are mounted on their ends. Proceed with the assembly as per board 1. The piezo buzzer can either be mounted on the board or externally (eg, on the case) via flying leads. Note that there is provision for mounting a serial EEPROM (IC5) and two resistors (R58 & R59) on the bottom of the board but they are not used in this particular application. Eight 1kΩ resistors and 21 wire links are used to bridge the two PC boards (component lead offcuts can be used for the links). After carefully inspecting both boards for the usual soldering mishaps place both boards back to back and use the spacer and screws to join both Parts List For Non-EFI Option (PC Board 3) 1 PC board (coded QIP3) 10 63mm lengths tinned copper or hookup wire Semiconductors 1 4020 (IC8) 1 MAX232 (IC6) 1 TL082 (IC7) Capacitors 6 10µF (C15 - C20) Resistors 4 10MΩ (R46, R49, R54, R57) 8 1kΩ (R47-R48, R50-R53, R55-R56) 1 22Ω (R60) boards together. This done, install resistors R60-R67 (1kΩ), then install the wire links. The boards have plated-through holes so all soldering can be done from the outside but before final soldering make sure both boards are parallel to each other and aligned correctly. There should be exactly 10mm between the PC boards. If the third PC board is being used, assemble it in the same way. PC stakes should be installed on the back of the board for external connections. PC board 3 is mounted with its components facing forward and linked to PC board 2 via long lengths of tinned copper wire. The two boards should be exactly 60mm apart. There is an obvious danger of the tinned copper wire shorting but when assembled in the case, the wires can be bent out of each other’s way. They are rigid enough to stay in the same position. However, if you have any doubts at all, some or all of the tinned copper wire can be replaced with insulated hookup wire or you could slide an insulation sleeve over each length of tinned copper wire before soldering it in. Mounting in the case Before installing the two or three PC boards in the case, the bottom screw lugs need to be removed from inside the case so that the display board is clear of them. The lugs can be drilled or filed down. April 2000  67 This is the optional PC board 3 for non-EFI vehicles, also shown samesize. The connecting links (shown in green) back to PC board 2 need to be about 63mm long to allow the boards to mount 60mm apart and so fit into the slots in the case. IC8, shown in blue, is not required in this project nor included in the kit. Its job was to divide and shape incoming pulses but was found to be unnecessary. If the computer is to be used for general-purpose data logging applications (as it can be) this facility could be quite handy! You will need to drill out a small hole on the back panel of the case so that the 6-core cable can enter the computer from behind. Use a grommet on the back panel to secure and protect the cable. A logical colour code for the 6-core cable is given in Table 1. Testing Much of the testing is undertaken using the computer’s own diagnostic functions. These tests are undertaken BEFORE the computer is installed in a vehicle. Follow the steps below for a thorough testing procedure: Step 1: apply +12VDC and ground to the respective inputs. Nothing should happen Step 2: apply +12V to the accessory input. You should hear a BEEP out of the computer and a message displayed on the display “tRiP 1.0” – Trip computer, version 1.0. Disconnecting the accessory input from the +12V should shut the computer down. Step 3: check that the keyboard is functioning correctly by pressing every key; a BEEP should be heard every time a key is pressed. Use the Diagnostic Menu Option 4 to check all the key combinations. Step 4: check the display and use Diagnostic Option 5 to cycle through all of the display. Step 5: check the speed input by using Diagnostic Option 1 and pulsing the speed input with a voltage of 5-12VDC. The display should register the pulses. Remember the display might jump up very quickly because the input is very sensitive. Step 6: check the fuel input by using Diagnostic Option 2. If the computer has been configured for EFI operation, pulse the input with a 5-12VDC signal to trip the counter. If a Flow Sensor is connected blow into the sensor and it should register on the display. Step 7: test the display-dimming feature by connecting +12VDC to the headlight input. Testing is now complete. If all tests were satisfactory the computer can now be installed into a vehicle and calibrated. Speed calibration Speed sensor calibration can be achieved in two ways. The first method involves using the Cal Menu Option #1 automatic calibration mode. This requires you to drive a known distance while the computer counts the pulses from the speed sensor. Your local motor registry or transport department should be able to tell you where an accurate “speedo calibration” stretch of road is located (most are on freeways). Alternatively, most taxi companies have a known length of road for calibrating taxi meters. Also most new cars have a quite The two boards have to be exactly 10mm apart and exactly parallel. Here you can see how the 10mm spacer, resistors (which are actually 1kΩ now) and the wire links (cut-offs from resistors) achieve this spacing. It’s very rigid, too. 68  Silicon Chip Table 1: Wiring Colours Colour Connection Orange Green Blue Brown Black White +12V DC Ground +12V DC Accessories Speed Sender Fuel Injector Headlight accurate speedo (odometer) but older cars may not be so good. During calibration, the computer displays the message “DiSt”, “CAL”, “value” where “value” represents the number of pulses received from the speed sensor. Once the known distance has been travelled, the Mode/Enter key is pressed to end counting and the distance travelled is entered. The computer divides the distance travelled by the number of pulses counted and stores the value as a calibration number. It is a good idea to record the Distance Calibration number using Cal Menu Option #2 – View Modify Speed Sensor Calibration number, so that if power is lost you can manually enter the number into the computer without having to repeat the entire calibration process. The second calibration method is to manually calculate how many milli­metres each pulse from the speed sender represents and entering the value in number of mm’s using Cal Menu Option #2. This number can be calculated by measuring the diameter of the tyre and dividing that by the number of sensor pulses per wheel revolution. This method is not normally as accurate as the first method. EFI Calibration Follow these steps to calibrate the Table 2: Resistor Colour Codes       No. 1 (or 5*) 2 9 23 10 (or 18*) 8 (or 9*) Value 10MΩ 33kΩ 10kΩ 2.2kΩ 1kΩ 22Ω 4-Band Code (1%) brown black blue brown yellow yellow orange brown brown black orange brown red red red brown brown black red brown red red black brown 5-Band Code (1%) brown black black green brown yellow yellow black red brown brown black black red brown red red black brown brown brown black black brown brown red red black gold brown (* extra resistors required if PC board 3 is used) April 2000  69 Here are the three PC boards mounted in the case, complete with the red acrylic filter. Note that the filter is in the first slot. The display PC board is not in any slot but is held in place by the second PC board 10mm behind it in the second slot. The optional third PC board is in the third slot with the back panel in the fourth. computer for EFI operation: Step 1: fill the fuel tank (ie, all the way to full. Step 2: ensure the “EFI” Mode is selected (Cal Menu Option #7). Step 3: select the Fuel Calibrate Mode from the Cal Menu Option 3 to start calibration. During calibration the message “Fuel”, “CAL”, “EFI”, “value” will be displayed. The “value” represents the total pulse width time. This value must not exceed “4294”. Drive the vehicle for as many trips as required until 80-99% of the fuel tank is used or the value approaches “4294”. If you exceed the value of “4294” then an error message will be displayed and you will have to start calibration again. When the value reaches “3500” the computer will beep to indicate that it is approaching the end of its calibration range. Step 4: fill the tank to the same point again and note exactly how much fuel was used. Press the Mode/Enter key and then the computer will ask you to enter the Fuel Used. This completes fuel calibration. It is a good idea to take a note of the fuel calibration number using Cal Menu Option 4 in case the computer loses its settings – you can manually input the calibration number without having to recalibrate the computer. Fuel flow sensor calibration To calibrate the computer for Flow 70  Silicon Chip Sensor Operation you will need to know the calibration number of the sensor being used which is number of pulses the sensor emits per 100ml of fuel used. The sensor used by Oztechnics, for example, has a fuel calibration factor of 780. Step 1: ensure the “FLO” Mode is selected (Cal Menu Option #7). Step 2: select the Fuel Calibrate Mode from the Cal Menu Option Step 3: enter the flow sensor calibration factor. That's all there is to sensor calibration. Engine tacho calibration (EFI mode only) The Engine Tacho is only operational in the EFI mode as the injector frequency is also used to determine the RPM of the engine. A calibration number, which for most engines will be 120, must be entered into the computer. Enter this number using the CAL Menu option #5. The maximum value is 255. The calibration number may be different for some EFI systems which fire the injectors more than once per cycle. The calibration number for these engines may need to be determined by trial and error. If the flow sensor mode is used, you can enter 1 to display the frequency of the flow sensor or 60 to display the RPM of the sensor. Serial data link & logging A Windows 95/98 Virtual Dashboard application can be used to display the OzTrip Computer’s Telemetry. It is also possible to control the OzTrip from this application. A 2-way serial data link is used between the OzTrip Computer and a PC and the data from the microcontroller needs to be RS232-translated. This is achieved via optional PC board 3. This PC board and the optional software are available separately. The Virtual Dashboard Visual Basic source code is also available separately so that it can be customised for individual applications. We plan to present another part to the OzTrip Computer in a future issue detailing the use of the Virtual Dashboard and describing remote monitoring/control. Errata The following recent amendments should be noted for the circuit diagram published on pages 90-91 of the March 2000 issue: the 10kΩ resistors to the bases of Q5-Q12 and Q13-Q20 have now been changed to 2.2kΩ. Also, power to the TL082 (IC7) pin 8 on board 3 has been changed: it is now taken not from the +5V rail as shown but from +12V via the ignition switch, through a 22Ω resistor (R60) decoupled by a 10µF electrolytic capacitor (C15). Finally, the 5V supply to the MAX232 (IC6) goes direct to pin 16, not pin SC 2 as shown. Where To Buy The Parts A full kit of parts can be purchased from Oztechnics Pty Ltd. You can place your order on-line from the Oztechnics secured web server or make inquiries via email. Visa, MasterCard and Bankcard accepted. All components, case and laser cut front panel filter are included in the kit. Note: this project and software is copyright to Oztechnics Pty Ltd. Description OzTrip Computer Kit (boards 1 & 2).......................................................$129 PC board 3 Kit........................................................................................$59 (a) (Signal Conditioning & Serial Data Comm’s PCB kit + PC software) Fuel Flow Sensor....................................................................................$119 (b) Proximity Switch (speed sensor)...........................................................$30 Oztechnics V2.0 Car Computer Kit (LCD Model)....................................$179 P&P........................................................................................................$10 (a) & (b) are required for fuel flow installation. (a) is required for data logging. Oztechnics Pty Ltd, PO Box 38, Illawong, NSW 2234. Phone: 02 9541 0310; Fax: 02 9541 0734. Website: www.oztechnics.com.au  Email: info<at>oztechnics.com.au April 2000  71