Author: Li Gang
1. The principle of the circuit This stopwatch is displayed with a light-emitted digital tube, and the timing accuracy is one percent, the maximum timing time is 9.99s. The schematic diagram of the circuit is shown below. The circuit consists of a clock circuit, a count / decoding / display circuit, a manual timing control circuit. The clock pulse generator constitutes a crystal oscillator to generate 38,000 to Hz pulse signals, and then generate a cycle of one percent of the clock signal of the CD4040 count / divider. The clock pulse is output to the CD4033 count / decoding / display circuit, which is displayed by 7 segments. Press the timing button an1, stopwatch begins the timing; then press the stop table stop counting, while the timing results are displayed. Press the clear recovery button AN2, the display result disappears, and the stopwatch returns 0 value.
(1) How to get the key to the clock pulse signal stopwatch is to obtain an accurate clock signal. This circuit uses CD4069 to form a quartz crystal oscillator circuit, generates a pulse signal of 38000 to _{z; and then passing the frequency division of 380 by CD 4040, a clock pulse signal having an output period of 0.01 seconds. (2) How to design a divider circuit in divider circuit of 380 is 380001- {z door 00Hz = 380. The steps of the divider using 4040 in the frequency division coefficient of 380 are as follows. The division coefficient 380 is 200, and the number of applications: 380 = 10111100, = 2 (8) +2 (6) +2 (5) +2 (4) +2 (3) +2 (2). Plus the index of the six multiplines in the above formula 1, i.e., add 8, 6, 5, 4, 3, 2, respectively, 9, 7, 6, 5, 4, 3; thus determining Q9 using CD4040 , Q7, Q6, Q5, Q4, Q3 These 6 output terminals. (3) Stopwatch Control Circuit - On Key Circuit Manual Meter The function of the button circuit is the operation stopwatch. Press the stopwatch to start the timing, then press the stop table stop meter and display the time elapsed twice. This circuit is adopted. 4069 forms a dual steady memory circuit, combined with the use of a normal button switch AN1 to form a key circuit. Every time you press this. The output potential of the CD4069 door 6 changes a state between the high potential and low potential; this output electrical signal is connected to the reset end of the CD4040 divider. When the reset end of 4040 is a low potential signal control, it can count normally; when the reset end of the CD4040 is high potential signal control, it stops counting. (4) Clear recovery button circuit Its function is to clear the counter after the timing is completed, so that the next timing work is ready. The circuit is composed of a pull-down resistor R and a conventional button switch AN2; it is usually controlled at a low potential due to the action of the pull-down resistor R6, and if there is a clock signal input from the input terminal, the CD4033 counts normally; Move this button, the reset end of the 3 CD4033 get a high potential pulse, thereby enabling the outputs of each digit of the CD4033 counter to become 0. (5) Decociation count / 7 segment lesson integrated circuit CD4033 features
The pin wiring diagram of the CD4033 is shown in the following figure (omitted).
It can complete the decimal count function, decoding, and display driving. The main pin function is as follows: CP: Counter clock input; inh: counter clock is prohibited, high power is effective: RBI: zero-elongated end, low power is effective: RBO: Moves hidden level continuous output; CO: count dozen Revenue output; A-G: 7 paragraph Arabic digital code, output high level when displayed; LT: Display test end, high power is effective; R: Reset, high power is effective. The unique feature of the CD4033 is to set a separate zero-hidden function and multi-bit connecting blanking functions to save power. The "second" bit in this circuit sets a zero blanking function: This function is not set behind after the decimal point. The current of the CD4033's decoded drive circuit is much smaller than the integrated circuit such as CD40110, and the CD4511 is used. If used 5V supply voltage, 4033 drive current is up to 3 mA, and two of the two 20 mA. This feature of CD4033 has now become an advantage. It turned out that for the digital tube to display enough brightness, the drive current of each segment code generally requires 15mA; the driver current of the segment code is up to up to. 100RNA. If 4-bit digital tube is used, the total drive current is up to 400mA; so the circuit with the digital tube is rarely supplied with the battery. Even so, the light emitted by some old digital tubes is still not bright outdoors. With the appearance of ultra-high brightness LEDs, some new digital tubes also use ultra-high brightness light-emitting chips; each segment code is available with 15mA operating current, which is sufficient to ensure that it can be recognized outdoors. Experiments have proven that the ultra-high brightness digital tube is used, and each segment code can be used indoors with only 1mA drive current; it is more than enough to drive with CD4033. Thus, according to the average current of each digital tube is 5mA, the driving current of the 3-digit stopwatch is only 15 mA, and the No. 5 battery can be powered. This work uses a 1/2 inch ultra-high brightness common cathode digital tube, and the luminescent color is not limited.
The native digital tube is 8 segments, and there is a decimal point on each of the digital tubes; only the decimal points in the second digital tube.
2. The assembly circuit (1) component layout on the assembled panel is first determined according to the number of components of the circuit diagram, and can be assembled with a wide line panel. The order of the layout of components on the breadboard is first installing the integrated block: first according to the circuit diagram to determine the position of each integrated circuit, then insert an integrated circuit. It is recommended to install IC1 ~ IC8 in order from left to right: ie CD4069, CD4040, CD4033, digital tube (one percent), digital tube (one tenth of second), CD4033, digital tube (second), CD4033 ;As shown below. For connecting, the digital tube is inverted; that is, the decimal point is above. Therefore, the order of the 3-bit CD4033 is the second place at the right side. When you are inserted, you can display the results of the stopwatch by normal numbers. (2) Assembling the connection and debugging the elements such as the resistance capacitor while using the bread line. It is recommended to step by step, step-by-step debugging. The first connection number of digital tube and drive circuit is completed, and the power supply is debugged. The debugging method is to connect one end of a bread chart in the count input of the CD4033, and the other end is first plugged in positive, and then it is then grounded; the 3-digit digital display tube should display the number change, indicating that this part of the circuit is working properly. The second step wiring clock circuit is debugged. The successful mark is a digital tube to display one percent. Last connection stopwatch control circuit to implement a stopwatch with two buttons. 3. The accuracy of the assay stopwatch can be accurately debug the homemade stopwatch with another stopwatch. For example, use the mobile phone stopwatch, use both hands to control the mobile stopwatch and homemade stopwatch, press the start of the time, and press the stop button after 10 seconds; if the homemade stopwatch is different from the mobile phone stop, it can be considered Successful production. If the error exceeds 0.1 seconds, the circuit should be checked to find the problem.
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