Introduction:
Now, many people use a bicycle as a sports program that exercise. If you install a mileage schedule on your bicycle, you can know the speed and stroke of your own cycling, so that the amount of exercise is well controlled. This article describes a bicycle mileage table for a single chip microcomputer. Miles and speed display can be switched, using a three-digit digital tube display, the maximum display has 99.9km. The maximum display can be 99.9km / h. The miles can also be used on a motorcycle that does not exceed 100km / h in electric bicycles and speeds.
Circuit principle:
The circuit is shown in Figure 1. Composed of detecting sensors, single chip circuits and digital display circuits.
The detection sensor consists of a permanent magnet and a switched Hall integrated circuit UGN3020.
The UGN 3020 is composed of a Hall element, an amplifier, a plastic circuit, and a collector opening output circuit.
Its function is to convert the magnetic signal into an electrical signal. Figure 2A is a block diagram thereof. The Hall element H is a magnet-sensitive element. When the magnetic field intensity perpendicular to the Hall element changes, the voltage at both ends changes, and after amplifying and plastic, the pulse power signal can be output at the 3 pin. The working characteristics are shown in Figure 2B. Due to a certain hysteresis effect. It can guarantee that the switch has no jitter. BOP is the magnetic field strength of the work point "open", and BRP is the magnetic field strength of the release point "off". The permanent magnet is fixed to the spoke of the wheel, and the UGN 3020 is fixed to the fork of the wheel.
The working principle of detecting the sensor is as follows: The wheel is transferred one week, the magnet passes through the UGN 3020, and the 3 foot outputs a pulse signal. The UGN 3020 outputs the pulse signal as an external interrupt signal of the single-chip AT89C2051. Enter from P3.2. Single chip measures the number of pulse signals and pulse cycles. The mileage is calculated based on the number of pulse signals, and the speed is calculated according to the cycle of the pulse signal and the digital tube is sent. SL is used to switch between mileage and speed display, and the speed is displayed in the initial state. Digital tubes DSL ~ DS3, VTL ~ VT3, R4 ~ R13, etc. constitute a display circuit. Use a common male digital tube. P3.3 ~ P3.5 is driven by the dynamic scanning position of the digital tube. P1.0 ~ P1.6 Digital segment code output.
programming:
The program is written in C language, consists of a main program, an external interrupt O service program, a 11D interrupt service, a delay subroutine, and other modules. The main program mainly completes the program initialization and keyboard processing.
The external interrupt O service program consists of part of measurement, calculation, reading, etc., and the TO interrupt service program consists of time, dynamic scanning display, bicycle parking judgment and other parts.
The pulse signal input from the P3.2 port is the interrupt request signal of the external interrupt O. Using the edge trigger mode. When the measurement speed is measured, since the frequency of the wheel rotating pulse signal is very low, the measurement is not suitable for use, and the measurement is performed using the method of the test pulse cycle. The pulse signal system is used to control the timing signal. The pulse cycle is calculated by the timing number, and the travel speed of the bicycle can be obtained by dividing the circumference of the wheel. When measuring mileage, the number of pulse signals can be used by the circumference of the wheel. It should be noted that the pulse signal cycle and number are simultaneous measurements. It is only to switch the display with the button switch SL.
The interrupt timing time of the timer TD is 5 ms, each time the timing variable N plus L, so the unit of n is 5 ms. For example, the N value corresponding to the bicycle wheel is 100. The corresponding time is 0.5 s. From this, the speed of the bicycle is 14.9km / h. If the value of N reaches 1000, the external interrupt does not occur in 5 seconds, that is, the bicycle is not advanced. N is also cleared, the speed is displayed as O. The reading is displayed in three digits, and the TD is interrupted once. Data can be refreshed 3 times. That is, 15ms refresh the data.
Editor in charge: WV, read full text
Our other product:
