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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING Laptop - trip computer. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Automobile. Electronic devices Some models of VAZ vehicles are equipped with a trip computer MK-21093. This device, processing the signals of speed sensors (DSA) and fuel consumption (DRT). displays on the indicator the elapsed time since the beginning of the trip, the distance traveled, the average speed, the consumption of gasoline (instantaneous, per trip or average per 100 km). Modifications of the computer for cars of the VAZ-2110 family measure, in addition, some other parameters - the voltage of the on-board network, the temperature in the cabin and overboard. All this information is certainly useful, but, unfortunately, only one of the parameters is displayed on the indicator at a time, and it is difficult to determine which one at a glance. Yes, and you have to switch modes almost blindly. The inscriptions above the buttons are almost invisible, especially in poor lighting conditions. And in order to choose, for example, the most economical driving mode, the driver has to constantly monitor the computer indicator, being distracted from the road, and this is already unsafe. Using such a trip computer, the driver after some time comes to the conclusion that the device, of course, is interesting, but ... not needed. Another thing is if the readings of the sensors could be recorded in a kind of "black box", and reproduced after the trip. There would have been an opportunity in a calm environment to identify all the patterns and take them into account in future trips. There is also a legitimate desire to quickly receive information, for example, about the remaining gasoline in the tank or the distance that can be driven on it. It would be nice to have a sound signal about that. nu the specified distance has been traveled, the specified speed has been reached (or exceeded). And if you install additional sensors, you can measure and display much more, up to the position of the car on the city map. The idea to modify the existing on-board computer was quickly discarded. The fact is that the basis of the computer is a specialized microcontroller KR1820VEZ-021 with a masked ROM. the program of which is very difficult to "hack", but even more difficult to rework. Even if it were possible to replace the microcontroller with another, say, the KM 1830 series, the limited capabilities of the indicator (only four decimal places) and the insufficient number of control buttons on the front panel of the computer would still not allow anything to be improved. As for the recording of sensor readings, the work on the manufacture of this system would have to start from scratch. In general, one thing remains - to create a trip computer again. But before you "forge iron", it's a good idea to check in practice and work out its basic algorithms. And for this, a laptop computer with a large LCD screen and a full keyboard is best suited. You just need to find a way to connect it to the sensors installed in the car. To develop and correct the program of such a computer, all known programming tools for the IBM PC are suitable. The accumulated information is written to a flexible or hard disk (in an effort to protect disk drives from damage, it is better to do this during stops, at least at a traffic light). If you wish (and have the means), you can record on solid-state memory cards that are not afraid of mechanical stress. The recording is played back on the same or any other computer, and any methods of mathematical processing and analysis are available here. The DSA of the trip computer MK-21093 is mounted on the speedometer shaft, which makes one revolution per meter of travel. The sensor output circuit closes and opens ten times per revolution, generating 10000 pulses per kilometer. DRT from the same set generates 16000 pulses for each liter of gasoline passed through it. Both sensors require 12 V power supply from the car's on-board network. It is most convenient to send signals from sensors, as well as to press the brake pedal and reverse gear, to the inputs of the communication port available in each computer. The diagram of the interface device is shown in fig. 1. It is placed in any convenient place in the car, and the XS1 cable socket is connected to the computer's COM1 or COM2 plug. The CTS, DSR, DCD and RI port inputs are used to receive signals. The standard serial port adapter of an IBM-compatible computer is capable of automatically generating interrupt requests when the logic level changes on any of them. Optocouplers U1-U4 provide mutual galvanic isolation of car and computer circuits. The supply voltage of the collector and emitter circuits of the transistors of the optocouplers forms a rectifier on diodes VD1-VD6. For normal operation of the interface device, it is necessary to set opposite logic levels on any two of the three available outputs (TXD, RTS, DTR).
If the MK-21093 computer is already installed in the car and the sensors are connected to it normally. the necessary signals can also be removed from the MK, thus ensuring its simultaneous operation with a laptop computer. To do this, you need to supplement the interface node (Fig. 1) with two transistor inverters, as shown in fig. 2.
The outputs of the resistors, left according to the scheme, are connected to the indicated outputs of the DDI chip (K561TL1) installed on the processor board of the trip computer. Please note that it has two K561TTU chips. DD1 is the one that is located approximately in the center of the board. The +12 V voltage is supplied to the interface unit from pin 5 of the XP1 plug, and the common wire is connected to its pins 2, 7 or 8. In vehicles equipped with a General Motors electronic control unit (ECU), the DSA signal can be removed from pin B4 of the pink connector of this unit or from pin 2 of the eight-pin (white) connector of the instrument panel harness and engine management system. The DRT signal is removed from pin C2 of the blue ECU connector or from pin 3 of the mentioned connector. The DSA signal wire in the engine control harness is blue and red and has number 42. And DRT is yellow and black, its number is 71. To interface with the computer's COM port, it is permissible to use the already described node with the addition according to fig. 2. The source code of the TripCOM program module. processing the signals of the sensors is given in the table. During the initialization process, it requests and receives from the operating system the necessary amount of memory for data arrays, sets the desired mode of operation of the serial port, and uses the 06AH interrupt function 1 to configure the real-time clock in the computer so that they generate 4AH interrupt requests every second. The module automatically calls the NewExrtProc procedure before exiting. restoring the status quo.
Interrupts generated by the serial port adapter when any of the input signals change are handled by the NewComlnt procedure. It determines which of the sensors received the impulse, and increases the readings of the corresponding counter by two. The least significant digits of the counters do not participate in the counting of pulses. In one of them, the procedure writes a logical 1 if the brake pedal is pressed, and in the other - if the reverse gear is engaged. Every second clock interrupts are handled by the RTCAIarm procedure. reading the readings of the counters of impulses received from the DSA and DRT. Since the variables are reset after reading, the numbers that are entered into the arrays addressed by the pDIST and pFUEL pointers are proportional (excluding the least significant digits) to the distance traveled in the last second and the amount of fuel consumed during the same interval. The lower digits of the numbers indicate the state of the brake pedal and reverse gear. The W variable contains the index of the cell (the same for both arrays) into which the next entry will be made. After reaching the end of the array, its filling will start from the beginning. Since the size of a conventional array in an IBM PC cannot exceed 64 KB, it is necessary to rewrite data from RAM automatically or at the operator's command to a hard disk (or other external media) every 8.. 9 hours of continuous operation. Reading and processing data from arrays is the concern of the main program, which is not given due to the large volume. Our readers can find it on paguo.ru. She actively uses the TripCOM module. including the functions available in it for converting meter readings into instantaneous speeds in km / h (V). fuel consumption in l/h (Fh) and per 100 km (F100). The GX function returns the values of the longitudinal overload calculated from the DSA data (in units of q). occurring during acceleration and deceleration of the vehicle. The Brake and Reverse logic functions are true if the brake pedal is depressed or the reverse gear is engaged respectively. The GetSampIe procedure tells the procedures and functions mentioned above which meter sample to process and performs some preliminary operations on it. This procedure should be called every time the "second" being processed changes. The parameters of the sensors are given by the constants Nkm (the number of DSA pulses per kilometer) and N1 (the number of DSA pulses per liter of fuel passed through it). If the vehicle has sensors that differ from those included in the MK-21093 computer, it is enough to change the corresponding values in the constants section of the TripCOM module interface section. For example, to work with the ECU mentioned above, Nkm should be equal to 6000. A few words about the features of calculating the instantaneous fuel consumption per 100 km. In the corresponding formula, the speed of the car is in the denominator, so when driving slowly, the processor bit grid may overflow, and during stops it can be divided by 0. To avoid these errors, the MK-21093 computer calculates fuel consumption per 100 km of track only when driving at a speed over 27 km/h. In the function F100 of the module under consideration, measures against overflow are taken, and the returned value, regardless of the speed, is limited by the value of F100max (in our case, equal to 30 l). An example of graphs constructed according to the data recorded during the movement of the VAZ-21099 car along the streets of Moscow is shown in fig. 3. The speed curve due to the inertia of the car is very smooth, which cannot be said about fuel consumption. It is its unevenness that makes it impossible, looking at the constantly changing readings of the digital indicator of the MK-21093 computer. accurately determine the current value. Fuel consumption curve per 100 km. shown in fig. 3 is built on the average values over several minutes, which makes it more illustrative.
The trip took place in traffic during the morning rush hour. Fast traffic (sometimes exceeding posted speed limits) alternated with stops at traffic lights. One of them (at about 8 h 1 min) was overcome only in the second cycle of its operation. A few minutes, starting at 7:55 a.m. the car "creeped" in a traffic jam. In just 20 minutes, a little more than 11 km were covered and 1,3 liters of gasoline were used up. For comparison, when driving the same car at an approximately constant high speed (for example, along the Moscow Ring Road), 100 ... 5 liters of gasoline are consumed per 7 km. Statistical processing of the recorded data makes it possible to identify patterns of particular interest to drivers and automotive technicians. For example, in fig. 4 shows the dependence of fuel consumption on the average speed in the city, and in fig. 5 - from car acceleration during acceleration and engine braking.
The graphs are based on the average values of the parameters for several trips without additional processing (smoothing). Author: A.Sergeev, Moscow
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