In sheet piece machine pass software delay time, every other S of about 12.5 μ , p1.0 is taken turn over 1 times, can produce cycle to be the square wave of 25 μ S in P1.0 port so. As a result of 51 sheet piece machine I/O mouth exports way to be pulled on collector, electric current of tall n output is equal to on the electric current that helps resistance, this electric current is smaller. Low n output is the electric current that in-house transistor absorbs, can achieve 10mA greatly most, but the total electric current of whole port cannot exceed 24mA<1> . No matter be the pulls electric current or low n fill electric current of tall n can't direct drive ultrasonic launchs sensor, so need adds circuitry of enlarge of one class drive. If what drive circuit shows.
Drive circuit basically launchs transducer T to form by reverser 74ALS04 and ultrasonic. Odd after the 40kHz of an output of machine P1.0 port just crosses signal to pass one class reverser, send ultrasonic an electrode of transducer; Another classics two class reverser is junior the another electrode <2> to ultrasonic transducer. Fang Du with form of this kind of push-pull signal adds ultrasonic transducer two end, can increase the emissive strength of ultrasonic. Output end uses 2 reverser parallel connection, in order to increases drive capacity. Resistor R8 and R9 are pulled to be able to raise reverser 74ALS04 to output the drive ability of tall n on one hand on; Return the damp result that can increase ultrasonic transducer on the other hand, shorten the time <3> of its freedom oscillation.
Receive circuit ultrasonic to detect receive circuit to be core with CX20106A, if what logistic circuit shows <4> . Integrated circuit CX20106A receives signal frequency to be 38.3kHz, as more adjacent as ultrasonic 40kHz frequency, can detect completely with Yu Chaosheng wave receive. The signal that CX20106A inputs ultrasonic receiver undertakes enlarge, plastics and output, generation interrupts signal, by sheet piece time of echo of machine plan cipher out.
The main function that controls circuit to dominate circuit has: Implementation trends shows, signal of frequency of 40kHz of P1.0 mouth generation and with go up a machine communication. If what logistic block diagram shows. Indication part uses trends to show, in order to save sheet piece resource of machine I/O port. Paragraph the code arises by P0 mouth, choose signal to arise by P2 mouth. Information delivers the position of the movable awl to will detect to go up a machine, use ultrasonic of circuit of emissive circuit drive to receive systematic casing chip, implementation is odd a machine and go up a n changeover between machine, implementation is odd a machine and go up a machine communication.
Using temperature compensation to have school of velocity of sound is the similar concern V=331.45 0.607T according to temperature and velocity of sound, or V=20.067T/2, computation gives <5> of actual velocity of sound, achieve pair of velocity of sound to have compensatory objective. Specific implementation: In fluid survey a system adscititious a temperature is collected implement, the temperature that measures an environment changes. Ultrasonic fluid plan when the job, the environmental temperature at that time the value changes signal of amount to word to convey odd a machine, by sheet piece the actual velocity of sound that machine computation gives this temperature to fall. Express the 1 ultrasonic velocity of sound that listed a few kinds of different temperature fall.
Program of range finding of software design ultrasonic basically includes main program, ultrasonic happening program, delay time program, distance computation program and indication program. Main program function is systematic initialization, mode of set timer job, leave to always be interrupted, call ultrasonic happening program next, send 4 periodic ultrasonic signal, open timer 0, outside be being opened after delay time 0.1ms, the ministry is interrupted 0, wait to receive returned ultrasonic signal <6> . Because here uses 12MHz any crystalline substance brace up, tally plan the time of a pulse is 0.1us. After receiving echo signal, the data of tally T0 is the time that ultrasonic transmits back and forth. If press normal temperature, supersonic velocity of wave is 344m/s, criterion fluid the distance to ultrasonic range finder is D=vt/2=172T/10000 (Cm) , in type: T is the computation of tally T0 to be worth. After measuring an interval, its will pile up means to send toward LED to show with decimal BCD as a result make an appointment with 0.5s, next reappearance ultrasonic pulse repeats measure. Give a space to be helpful for program structuralization and easy computation, the main program uses assembly language to write.
Test result puts ultrasonic range finder on the desktop, make probe to wait for measure an object, maintain 2 probe to be in go up point-blank together; Insert electrify source, digital canal can show emissive probe arrives need the test space that measures an object; Reoccupy is other measure a tool to measure an actual interval. Measure a picture to see. Through be being measured actually for many times, reach if express 2 kinds,actual distance and the specific data of indication distance are compared.
The measurement that epilogue designs originally blind area control is in 27cm less than, precision is measured inside 3m taller. Be aimed at diverse demand, still can increase emissive power, make metrical interval farther. Showing a side, can undertake altering appropriately to the program, the LED when making begin to launch ultrasonic shows temperature is worth, after should receiving ultrasonic echo, reach through computation distance, LED automatic switch shows the distance is worth, such is in visual effect admiral is more intuitionistic and clear.
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