Inspiration, capacitance, frequency measurement table based on STC89C52 / AT89S52
General measurement range inductance measurement range: 0.1μH ----- 1H small capacitance measurement range: 1PF ---- 2.2μF (non-electrolytic capacitance) frequency measurement range: 50Hz --- 400kHz (Measten Small Signal) Electrolytic capacitance measurement Range: 0.5μF - 12000μF (electrolytic capacitance, non-electrolytic capacitance) 1. Measurement principle 1, small capacitance, inductive measurement principle: circuit is an LC oscillator composed of LM393 (U3A). The frequency f1 of the LC shock loop is measured by the single chip microcomputer, and then the value of the inductance L1 according to the standard capacitor C1 [CREF] in the schematic.
The accuracy of the capacity of capacitor C1 is basically determined by the accuracy of the entire measurement process. A capacitor with high stability and high stability should be selected. The mica capacitor is generally recommended online, if you can't buy it, you can use the monolithic or CBB. Capacitor CX, the value of inductance Lx, calculated by the following sub-list:
Where f1 is an inherent frequency, F2 is an access test capacitor and the frequency after the inductance. 2, electrolytic capacitance measurement principle: The measurement of the electrolytic capacitance is based on the calculation of the time constant of the RC circuit. The charging speed of the capacitor is related to the size of R and C, the larger the product of R and C, the longer the charging time. The product of this RC is called the time constant τ of the RC circuit, ie τ = r ∙ c. If R's unit is used by Ohm, C, τ is set to second.
The illustration of the graph can obtain the general rules of the charging process: UC is rising according to the index law, the UC has changed faster, gradually slowed down, and slowly approaches its final value, when t = τ, uc = 0.632E ( E is a power supply voltage; this measuring instrument is to calculate the measured capacitance value by using the following sub-machine measurement UC = 0 to 0.632E, and calculate the measured capacitance value: the circuit is composed of comparator U1B, discharge transistors Q1, Q2. The set comparator positive input is UC, (UC = 0.632E, adjusting RREF), reverse input is connected to the capacitor CEX, when the single-chip P15 pin is low, the capacitor discharges. Note that the pull current of the 51 single-chip pin is small, and Q1 cannot be directly driven, otherwise the discharge time will be very long. When the single-chip P15 pin is high, the capacitor is charged. When charging to the UC, the comparator is flipped, and the external interrupt 0 is triggered, and the magnitude of the measured charging time and the charging resistance can be calculated. Second, the schematic
In the above figure (please refer to the PDF schematic), btn1 is a single-chip reset button; BTN2 is a calibration button, and it can be pressed at any time when the measurement small capacitance is pressed. BTN3 is a function switch button to measure LCF (frequency, small). Capacitor, inductance) and measuring electrolytic capacitors switching. The three double-throw switches in the figure are used to switch the measurement, S1 switches between the L, C (small capacitance), S2 switches between the frequency and the LC, switch between large electrolysis and small electrolysis; single-chip The type of measurement is automatically determined according to the status of the switch and the button BTN3. In addition, FX, CX, LX have a GND terminal, and four terminals on the board are close to each other, and can also add more GND terminals, not shared, and wiring can be flexible according to the actual situation. Third, the surface comparator peripheral components are more, the wiring may be less convenient, providing you with a reference for the LM393 around the component, such layout is not too much. The flying line on my board is mostly because the analog power supply and the digital power supply have been more stringent. It is actually not necessary, but the power and ground near the LC oscillator circuit must pay attention to isolation, otherwise the small capacitive reading may be very small. Unstable! Standard Capacitance CREF is preferably used with 2200PF mica capacitors, the accuracy of the capacitance directly determines the measurement accuracy of small capacitance and inductance! (However, it does not affect the frequency and electrolytic capacitance measurement accuracy.)
RREF debugging method, in principle, the comparator is in phase input voltage UC = 0.632E (power supply voltage). IV. Use method to measure small capacitance, inductance, frequency is a set of functions, specifically measure which one is determined by S1 / S2, which is automatically identified according to the state of S1 / S2. The large electrolytic capacitance and the small electrolytic capacitor are a group, and the electrolysis is specifically measured or small electrolysis is determined by the S3 state. The function switch button (BTN3) is required between the two sets of functions to switch. 1. The power-on power-up interface shows the Chinese electronic DIY home website and the avenue member number.
2. At this time, S1 / S2 / S3 is placed in a pop-up state at this time, and S1 / S2 automatically displays other measurement interfaces (frequency fx or the measurement interface of the inductor Lx) when S1 / S2 is in other states. 3.7PF in the figure is an unclear error, and generally this value is relatively large, and the small capacitance and inductance can be measured after calibration. Frequency gear and electrolytic capacitors do not require calibration, calibration only for small capacitors and inductance measurements.
3, small capacitance, inductive calibration calibration only needs to be calibrated (Clear) button when the measurement capacitor is not accessed (the schematic) button (the BTN2) is automatically cleared when the measurement capacitance is not accessed. (Shown below). The terminal Lx of the sensing power is shorted to the GND in the inductor calibration, then press the calibration button, because it is inconvenient, so it does not advocate the inductive calibration. In small capacitors and inductor calibrations are equivalent, after small capacitors are calibrated, press S1 to measure the inductance, and no calibration is required.
4, the measurement small capacitance S1 / S2 is populated, and the single chip automatically displays the measured capacitor interface unless the function switch button (Schematic BTN3) is switched to the electrolytic capacitor file. After calibration, the small capacitance is directly connected between the CX and GND, and the following figure shows. The first line shows the measured capacitance value, and the second line shows the frequency of the current LC oscillation circuit.
5, the test S1 is pressed, the S2 pops up, the single chip automatically displays the sensing input sensing interface unless the function switch button (Schematic BTN3) is switched to the electrolytic capacitor file. The inductor is connected between the LX and the GND, and the figure below is shown. The first line shows the measured inductance value, and the second line shows the frequency of the current LC oscillation circuit. The measured inductance and the circuit board are the same, and the inductance of a nominal 100UH is given.
6. The measurement frequency is pressed (S1 state independent), and the single chip automatically displays the measurement frequency interface unless the function switch button (Schematic BTN3) is switched to the electrolytic capacitor file. This measuring instrument can measure the signal, the frequency measurement range of 50 Hz to 400 kHz, and the measurement accuracy is within 0.2%. This is the interface that tests the 20kHz signal.
7. Measuring the small electrolytic capacitor at any of the small capacitance, inductance, and frequency, press the function switch button (the BTN3 in the schematic) to switch to the state of the electrolytic solution, and then bounce according to the S3 bomb or pressed state automatic Identify the measurement of electrolysis or test the small electrolytic capacitance. Press the function switch button again (the BTN3 in the schematic) will return to the state of the small capacitance, inductance, frequency. This is the role of the function switch button. In addition, other measuring gear single-chip features can be pressed or bounce automatically according to S1, S2, S3, and there is no need for human intervention. When the S3 bounces, a small electrical deconment is measured, the first line shows the measurement range, and the second line shows the measured capacitance value. After taking the photo, the procedure is slightly changed, and the scope of the display will be slightly different.
8. The measurement of the large electrolytic capacitance function is switched in the measurement electrolytic capacitor state, and S3 is pressed, automatically enters the large capacitor measurement interface. After taking the photo, the procedure has changed slightly, and the range of measurements has increased to 12000 uf.
5. Other instructions This production can be made using STC89C52 or AT89S52, and. HEX file can be burn directly. If you encounter any questions during the imitation, please leave a message, I will reply the first time after I see it. Attachment: Production Process Show 1, Component Show
2, the welding completed frontal flying line is mainly a digital power source and digital ground, because the digital power supply is strictly isolated from the analog power supply, so the flying line is more chaotic. Do not isolate a lot, you can connect together, the board can be more beautiful.
The flying line on the back is mainly button line, signal detection line, ISP serial download line, etc., the simulation section tries to avoid the flying line, or uses short flying lines.
3, load chip and 1602, read full text, original title: Based on 51 single-chip capacitor, inductor, frequency measuring instrument (LCF table)
Article Source: [Micro Signal: GH_DAE0718828DF, WeChat public number: MCU fan] Welcome to add attention! Please indicate the source of the article.
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