555 timer IC
Article by jekky
UsagePinout diagramThe connection of the pins is as follows:Nr.NamePurpose1GNDGround, low level (0 V)2TRIGA short pulse high-to-low on the trigger starts the timer3OUTDuring a timing interval, the output stays at +VCC4RESETA timing interval can be interrupted by applying a reset pulse to low (0 V)5CTRLControl voltage allows access to the internal voltage divider (2/3 VCC)6THRThe threshold at which the interval ends (it ends if the voltage at THR is at least 2/3 VCC)7DISConnected to a capacitor whose discharge time will influence the timing interval8V+, VCCThe positive supply voltage which must be between 3 and 15 V Monostable modeSchematic of a 555 in monostable modeThe relationships of the trigger signal, the voltage on C and the pulse width in monostable modeIn the monostable mode, the 555 timer acts as a ne-shot pulse generator. The pulse begins when the 555 timer receives a trigger signal. The width of the pulse is determined by the time constant of an RC network, which consists of a capacitor (C) and a resistor (R). The pulse ends when the charge on the C equals 2/3 of the supply voltage. The pulse width can be lengthened or shortened to the need of the specific application by adjusting the values of R and C.The pulse width of time t, which is the time it takes to charge C to 2/3 of the supply voltage, is given bywhere t is in seconds, R is in ohms and C is in farads. See RC circuit for an explanation of this effect. Astable modeStandard 555 Astable CircuitIn astable mode, the ’555 timer’ puts out a continuous stream of rectangular pulses having a specified frequency. Resistor R1 is connected between VCC and the discharge pin (pin 7) and another resistor (R2) is connected between the discharge pin (pin 7), and the trigger (pin 2) and threshold (pin 6) pins that share a common node. Hence the capacitor is charged through R1 and R2, and discharged only through R2, since pin 7 has low impedance to ground during output low intervals of the cycle, therefore discharging the capacitor.In the astable mode, the frequency of the pulse stream depends on the values of R1, R2 and C:The high time from each pulse is given byand the low time from each pulse is given bywhere R1 and R2 are the values of the resistors in ohms and C is the value of the capacitor in farads. SpecificationsThese specifications apply to the NE555. Other 555 timers can have better specifications depending on the grade (military, medical, etc).Supply voltage (VCC)4.5 to 15 VSupply current (VCC = +5 V)3 to 6 mASupply current (VCC = +15 V)10 to 15 mAOutput current (maximum)200 mAPower dissipation600 mWOperating temperature0 to 70 C DerivativesMany pin-compatible variants, including CMOS versions, have been built by various companies. Bigger packages also exist with two or four timers on the same chip. The 555 is also known under the following type numbers:ManufacturerModelRemarkCustom Silicon SolutionsCSS555/CSS555CCMOS from 1.2 V, IDD < 5 AECG PhilipsECG955MExarXR-555Fairchild SemiconductorNE555/KA555HarrisHA555IK SemiconILC555CMOS from 2 VIntersilSE555/NE555/ICM7555Lithic SystemsLC555MaximICM7555CMOS from 2 VMotorolaMC1455/MC1555National SemiconductorLM1455/LM555/LM555CNational SemiconductorLMC555CMOS from 1.5 VNTE SylvaniaNTE955MRaytheonRM555/RC555RCACA555/CA555CSTMicroelectronicsNE555N/ K3T647Texas InstrumentsSN52555/SN72555; TLC555latter: CMOS from 2 VUSSRK10061ZetexZSCT1555down to 0.9 V Dual timer 556The dual version is called 556. It features two complete 555s in a 14 pin DIL package. Quad timer 558The quad version is called 558 and has 16 pins. To fit four 555′s into a 16 pin package the control voltage and reset lines are shared by all four modules. Also for each module the discharge and threshold are internally wired together and called timing. Example applications Joystick interface circuit using quad timer 558The original IBM personal computer used a quad timer 558 in monostable (or “one-shot”) mode to interface up to two joysticks to the host computer. In the joystick interface circuit of the IBM PC, the capacitor (C) of the RC network (see Monostable Mode above) was generally a 10 nF capacitor. The resistor (R) of the RC network consisted of the potentiometer inside the joystick along with an external resistor of 2.2 kilohms. The joystick potentiometer acted as a variable resistor. By moving the joystick, the resistance of the joystick increased from a small value up to about 100 kilohms. The joystick operated at 5 V.Software running in the host computer started the process of determining the joystick position by writing to a special address (ISA bus I/O address 201h). This would result in a trigger signal to the quad timer, which would cause the capacitor (C) of the RC network to begin charging and cause the quad timer to output a pulse. The width of the pulse was determined by how long it took the C to charge up to 2/3 of 5 V (or about 3.33 V), which was in turn determined by the joystick position.Software running in the host computer measured the pulse width to determine the joystick position. A wide pulse represented the full-right joystick position, for example, while a narrow pulse represented the full-left joystick position. References^ van Roon, Tony, “555 Timer Tutorial,” p. 1.^ Scherz, Paul, “Practical Electronics for Inventors,” p. 589.^ a b |THE 555 TIMER IC – An Interview with Hans Camenzind^ van Roon, Tony, “555 Timer Tutorial,” Fig. 3 and related text.^ Jung, Walter G., “IC Timer Cookbook, Second Edition,” pp. 4041.^ van Roon, Tony, “555 Timer Tutorial,” at “Monostable Mode”^ van Roon, Tony, “555 Timer Tutorial,” at “Astable operation”^ Engdahl, Tomi. “PC analogue joystick interface, Introduction”. http://www.epanorama.net/documents/joystick/pc_joystick.html. Retrieved 2009-06-06. ^ Engdahl, Tomi, “PC analogue joystick interface,” at “Circuit diagram of PC joystick interface”^ a b Engdahl, Tomi, “PC analogue joystick interface,” at “Joystick construction”^ Engdahl, Tomi, “PC analogue joystick interface,” at “How PC joystick port hardware works”^ Eggebrecht, Lewis C., “Interfacing to the IBM Personal Computer,” at p. 197^ Engdahl, Tomi, “PC analogue joystick interface,” at “Introduction” and “Resistive analogue inputs (joystick position)”^ Eggebrecht, Lewis C., “Interfacing to the IBM Personal Computer,” at pp. 197-99 External linksWikimedia Commons has media related to: 555 timer ICData Sheet (Custom Silicon Solutions) (PDF)555 Timer Circuits – the Astable, Monostable and Bistable555 and 556 Timer Circuits555 Timer Pin configurationsData Sheet (Fairchild) (PDF)Java simulation of 555 oscillator circuit1972 Signetics NE555 datasheet (PDF)555 timer infoFrequency, and pulse time calculatorUsing NE 555 as a Temperature DSPFrequency and duty cycle calculator for astable multivibrators based on the NE555Timing calculator and visualiser for a 555 timer in astable modeHow to build a camera intervalometer using a 555 Categories: Oscillators | Integrated circuitsHidden categories: Articles containing potentially dated statements from 2003 | All articles containing potentially dated statements
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