"1 dry reed is a sensing element. When the magnet is close, the normally open contact is closed and the contact load connected to the through sensing circuit is only 10mA
2. Generally, the working voltage of toy DC motor is low. Although it can be started at 1.5 ~ 3V, the starting current is large (1 ~ 2a), and the operating current of motor under no-load is about 500mA
3. The maximum allowable collector current ICM of low-power silicon tube 8050 can reach 1.5A to meet the requirements of motor starting current
4 bimetallic lamination switch, closed when hot
5 generally, the photoresist, such as the 2 ~ 10K Ω light resistance of mg45 when illuminated by light, is an electronic component with rapidly increased conductivity under light irradiation. The commonly used model is mg45-1. When the working voltage is 5V, the current passing through shall not exceed 2mA
6. The resistance of water is about 50K Ω
7. Generally, the power frequency current below 8-10 Ma and the DC current below 50 Ma can be used as the safety current allowed by the human body every year. Generally, the human body resistance can be considered as 1000-2000 Ω
8 low voltage (5V) buzzer, its working current is only ten ma
9. The working current of relay coil (jrc-21f) is about 60mA, which is smaller than that of toy motor and larger than that of buzzer and led. The commonly used ultra-small low power relay is jrc-21f, the coil power supply voltage is 3V or 6V, and the contact works at 24V DC The coil resistance of 1A relay ranges from 10 Ω (3 ~ 6V) ~ 10 kiloohm (220V) 24V, about 1K, and the multi coil current does not generally exceed 100m
The difference between light-emitting diodes and ordinary diodes is that the forward voltage drop during conduction is relatively large, generally 1.5 ~ 2. V (about 0.7V for ordinary silicon diodes). The working current of LED is generally 10 ~ 40mA
The diode gear of the multimeter measures the voltage drop, and the on resistance of the diode is between 100 Ω or 1000 Ω
If the number tube is in the form of common anode, its driving stage shall be collector open circuit (OC) structure. If the number tube is in the form of common cathode, its driving stage shall be emitter output or source output circuit
13. The voltage stabilizing tube shall be connected in reverse in the circuit. The reverse breakdown voltage of the regulator is called the stable voltage
The bulb resistance of 14220v is about kiloohm (25 watt bulb resistance is about 2000 ohm, working voltage is 220 volts) and the current is 100 mA. The small bulb (3v-5v) resistance is 10 ohm and the current is 100 mA
15. The starting current of automobile starter is 200 ~ 600A
16. The coil resistance of motor shall not exceed 2 Ω, and the current is from a to 100 A. for 380V motor, 1 kW corresponds to 2 A
17 ignition coil primary coil resistance does not exceed 1 Ω, and secondary coil resistance is about 1000 Ω
18ic output capability output high level current
1974ls: 400ua (unable to drive the LED) (the output impedance (internal resistance) is 50 ~ 250 Ω (calculated according to the short-circuit current). The ability to carry the load requires that the load input resistance is greater than 12K (calculated according to the output high-level current 400ua) and the input resistance of LS is 250K (calculated according to the input high-level input current 20ua))
74hc: 4mA (output impedance (internal resistance) ten Ω（ According to the short-circuit current (calculated), the ability to carry load requires that the load input resistance is greater than 1.25k (4mA according to the output high-level current) and the input resistance of HC is 50m Ω (0.1ua according to the input high-level input current))
Output low level current 74LS: 8ma74hc: 4mA
IC output is equivalent to a power supply. The smaller the internal resistance of the power supply, the stronger the relative driving ability. Generally, the internal resistance of the power supply is less than 1 Ω. Generally, the input resistance of the intermediate stage of the circuit is relatively large, and the resistance of the output driving stage is large (bulb, relay) and small (horn, nozzle)
For a common emitter transistor, the input resistance is about Rb and the output resistance is RC
The emitter output input impedance is large, Rb + (1 + b) re output impedance is small < < re, so it has strong load capacity
The 20 electret microphone has a resistance of about 500 ~ 800 Ω, the output is 3 terminals, and the FET (impedance matching) is integrated inside
The resistance of loudspeaker is 2 Ω, 4 Ω, 8 Ω, 16 Ω, and the resistance of earphone is 20 ~ 600 Ω
21. The input resistance of the oscilloscope is 1m Ω
The input resistance of the voltage range of the digital multimeter is 1m Ω, and the output voltage is 0.65v when measuring the resistance
Diode output constant current source 1mA
22 for the speaker channel, it refers to the channel with different frequencies. The active speaker is a combination of amplifier and speaker
The headphone connector is a 3-core left channel, right channel and ground
23. The sensors can generate electrical signals (need amplification and shaping) and do not generate electrical signals
The amplification factor of the integrated operational amplifier is from 10000 to 100000, so there is a virtual short, and the input impedance is very large, so the input current is 0
25. The driving capacity of Zener diode shall not exceed 1a
26 counter can realize two functions, counting and frequency division.
Asynchronous counter: the speed of turning one by one is slow.
Synchronous counter: fast turnover speed at the same time.
BCD (decimal) counter: (0 ~ 9).
Binary counter (0 ~ 15).
Ripple counter: 7 levels, 14 levels and 21 levels
27 triode = transistor logic array = OC gate
9013(NPN)9012(PNP)
Maximum ic500ma
IB is microampere
Maximum vceo20v
8050(NPN)8550(PNP)
Maximum ic1.5a
IB is milliampere
Maximum vceo25v
2003 (transistor array) (NPN)
Maximum ic500ma
Maximum vceo50v (only used as a switch, not for amplification)
7407 (6 gate circuit buffer drivers OC gate)
Maximum output 40mA
Maximum vceo30v (less driving capacity)
284007 forward current 1a (rated)
Maximum forward current 30A
Maximum inverting voltage 700V
Forward voltage drop 0.9V
For rectifier clamp protection
4148 forward current 300mA (rated value)
Maximum forward current 2A
Maximum inverting voltage 75V
Forward voltage drop 0.7V
For small signal occasions
The voltage drop of LED is between 1.5 ~ 2.5V
The working current of LED is generally 10 ~ 40mA
The maximum input voltage of 297805 is 35V, which can provide 1.5A current (typically 500mA)
30 optocoupler 4n32 input rated current 60mA maximum forward current 3A reverse voltage 6vvceo30vic150ma
31 transistors are divided into bipolar transistors and field effect transistors. Field effect transistors are divided into Junction FET and insulated gate FET.
FET has large input resistance and small output resistance
32 negative feedback: voltage feedback is sampled from the collector of the later stage amplifier
Current feedback is sampled from the emitter of the post amplifier
The feedback signal connected to the transistor base is parallel feedback
The feedback signal connected to the transistor emitter is series feedback
Parallel negative feedback reduces the input resistance
Series negative feedback input resistance increases
The negative voltage feedback reduces the output resistance
The negative current feedback increases the output resistance
33 advantages of differential amplifier compared with direct cascade amplifier: suppression of temperature drift. The greater the re, the better the inhibition of temperature drift
A constant current source is equivalent to a large resistance
34 the amplification factor of the integrated operational amplifier is too large. In order to increase the input range, it must be connected in the form of feedback.
The output efficiency of 35 emitter stage is low, only about 20%
The push-pull output efficiency is high, reaching about 80%
Dual power supply: output without capacitance
Single power supply: output plus capacitance.
Integrated power amplifier lm384, 5W power output can be obtained on 8 Ω load, and 500 micro method capacitor shall be connected.
36 inverse proportional operation: voltage parallel negative feedback magnification - R2 / R1 input impedance R1 output impedance is small
Co directional proportional operation: voltage series negative feedback magnification 1 + R2 / R1, large output impedance and small output impedance
Voltage follower: like the emitter follower, the input impedance is large and the output impedance is small. Uo＝Ui
The amplifier can be used to form an active filter, a voltage source and a current source.
38 If the operational amplifier has negative feedback, the operational amplifier works in the linear region, active filter, voltage source and current source
If the operational amplifier has positive feedback, the operational amplifier works in the nonlinear region limiter voltage comparator (no feedback) zero crossing comparator hysteresis comparator (positive feedback) precision shaping circuit (feedback loop plus diode) waveform generation circuit.
39 power supply rectifier filter voltage stabilizing 78 series: the voltage difference between input and output shall not be less than 3V
408051 generally refers to 89C51 produced by Intel company, and refers to 51 series products produced by ATMEL company
41 single chip microcomputer reset circuit: complete with a 10u capacitor and 10K resistance, and add a 1n448. Reset time shall not be less than 5ms or 22u capacitor 1K resistance high-level reset: the capacitor is close to the power supply. Low level reset: the capacitor is close to the ground.
Addressing mode of 4251 single chip microcomputer: immediate, direct, register (register is faster than direct, direct and register are equivalent to putting data into a ram variable), indirect addressing (address is put in the variable, which is equivalent to pointer in C + +, in inter address addressing, only R0 or R1 can be used to store the searched data, (r register can be used as a register to control the number of cycles)), index addressing (used to look up the table movca, @ a + dptr), movdptr, # table (meaning of adding # label before label: label is an address!! For example, table is 100h #table is the immediate number #100)
Dptr in 4351 is a 16 bit register, which stores the address. The a accumulator must be used to access the external RAM
44sp should be initialized before use, indicating where the stack segment starts, such as movsp, #5fhorg indicates where the program segment starts.
The 45 shift command can be used for the lantern test.
46LJMP>AJMP>SJMP
Ajmp is a two byte instruction and LJMP is a three byte instruction,
47cjne: transfer after comparing two numbers are unequal (judge whether they are equal first, and then judge whether they are large or small, and jump with JC) djnz: transfer after subtracting 1 is not equal to zero, which is used to control the transfer instruction commonly used in cyclic digit operation: JB (transfer when bit is 1) JBC (transfer when bit is 1 and clear 0), which is used to clear the interrupt flag in query mode, Manual clearing is not required when using interrupt mode (0)
48 in bit processing, cy (i.e. carry bit of) is called "bit accumulator", which is equivalent to a in byte processing.
49 there are many restrictions on the operation of the counter / timer: 1. C / T switch 2. TR switch 3. Gate switch (when gate = 1, it is also controlled by INT1). Start T with setbtr0. There are 4 working modes: 0. 13 bit 1. 16 bit 2. Preset (the upper 8 bits are used for preset and the lower 8 bits are used for counting, so the range is small). It is generally used for baud rate generator 3. Timer 0 is divided into two independent timers / counters. Generally, when T1 works in mode 2, t0 works in mode 3. Registers for t: TCON control timer and interrupt tmod are mainly used to control the operation mode of T.
When the timer is used in interrupt mode, the work completed in interrupt: 1. Action 2 to be implemented after interruption. Reset the counter (equivalent to the work automatically completed in mode 2) 3. Set a soft counting cycle operation to output after multiple timings, which increases the timing time.
50 register for interrupt: ie: interrupt master switch IP: interrupt priority econscon
Interrupt program time cannot be greater than interrupt interval time
51 communication direction: in serial communication, the one-way transmission method in which the communication interface can only send or receive is called simplex transmission; The two-way transmission of data between machines a and B is called duplex transmission. In duplex transmission mode, it is divided into half duplex transmission and full duplex transmission. Half duplex transmission means that two machines cannot send and receive at the same time. At any time, the can only send or receive information.
52 serial port: mode 1: the shift register mode is externally connected with a serial in and parallel out shift register cd409474ls164 to expand a parallel port
53 the software removes the key jitter and determines whether to press the key again 10ms after it is found that the key is pressed.
After power on reset, the value in the program counter (PC) in 8051 is' 0000 ', so the program is always executed from the' 0000 'unit
55 carbon film resistance:
Low power 1 / 6,1 / 4W
1Ω～22M
Accuracy 5%
1 ~ 2 cents cheaper
Precision resistance
Low power 1 / 6,1 / 4W
1Ω～22M
High accuracy 1%
Five cents
Oxide film resistance:
1～2W
0.1Ω～22M
Accuracy 5%
Five cents
Cement resistance:
5～50W
0.11～1K
Accuracy 5%
Less than 1 yuan
Ceramic resistance:
50～200W
0.1Ω-1K
Accuracy 5%
Tens of yuan
2W high voltage resistance
270M
Accuracy 5%
5 yuan
Varistor
Accuracy 5%
Less than 1 yuan
Drain resistance (5-12 pins)
100Ω～1M
Accuracy 5%
5 points / foot
Adjustable resistance (horizontal and vertical)
100Ω-1M
Accuracy 5%
Less than 1 yuan
Precision resistors are generally selected for low-power resistors because they are not expensive.
Generally, the resistance is selected according to power: 1 ~ 2W oxide film resistance, 5 ~ 50W cement resistance and 50 ~ 200W ceramic resistance (too expensive)
56 capacitance:
Ceramic chip capacitor: 0.5p ~ 0.1U, withstand voltage up to 30KV, generally 50V
Polyester capacitor: 100p ~ 4.4u, the withstand voltage is generally 50 ~ 100V, and the maximum is 630V
Electrolytic capacitor: 0.1U ~ 22000u withstand voltage, etc
6.3v10v16v25v35v50v160v250v400v (no 15, 20)
Withstand voltage over 100V is very expensive, even hundreds of yuan
Tantalum capacitor: 0.1U ~ 100u, withstand voltage up to 50V, similar to electrolytic capacitor
Single stone capacitor: 10p ~ 2U, withstand voltage is generally 50 ~ 100V
Safety regulations are used for AC 250v0.01u ~ 2.2u
Resin for AC 250v0.1u ~ 47U
The smaller the capacitance, the higher the withstand voltage: the size of the capacity: Ceramic < monolith < polyester < tantalum < electrolytic tantalum and electrolysis belong to high-capacity capacitors
57 diode:
Rectifier: 1n40 series (1a) 1n54 series (3a) 1n526a series (6a)
Switch: 1N4148
Fast recovery: FR series (1a ~ 6a) fr10 * (1a) fr15 * (1.5A) fr20 * (2a) FR30 * () 3afr60 * (5a)
They are very cheap, no more than 50 cents
The withstand voltage of silicon rectifier bridge from 1A ~ 40A to 100V ~ 1000V shall not exceed 10 yuan
Zener diode: 2cw2dw
58 triode: too many models 2n (Japan, USA) B & times& times;（ Europe).
Medium and small power (less than 1W, current less than 1a, voltage generally not more than 100V): 90 series 80508550 of national half (slightly higher power is the derivative of 90) 2sc18152sc945
2n54002n5550 (higher withstand voltage than 100V)
The medium power is relatively small (the voltage of 1 ~ 1.5W is high, and the current above 200V does not exceed 0.5A). Used in color TV camera.
High power (above 5W) low withstand voltage
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