555 timer IC

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555 timer IC
Signetics NE555N.JPG
Signetics NE555 in 8-pin DIP package
Type Active, Integrated circuit
Invented Hans Camenzind
First production 1971
Pin configuration GND, TRIG, OUT, RESET, CTRL, THR, DIS, VCC
Electronic symbol
NE555 Bloc Diagram.svg
Internal block diagram[1]

The 555 timer IC is an integrated circuit (chip) used in a variety of timer, pulse generation, and oscillator applications. The 555 can be used to provide time delays, as an oscillator, and as a flip-flop element. Derivatives provide two (556) or four (558) timing circuits in one package.[2]

Introduced in 1972[3] by Signetics,[4] the 555 is still in widespread use due to its low price, ease of use, and stability. It is now made by many companies in the original bipolar and in low-power CMOS. As of 2003, it was estimated that 1 billion units were manufactured every year.[5] The 555 is the most popular integrated circuit ever manufactured.[6][7]

History[edit]

Die of the first 555 chip (1971)

The IC was designed in 1971 by Hans R. Camenzind under contract to Signetics (later acquired by Philips Semiconductors, and now NXP).[3]

In 1962, Camenzind joined PR Mallory's Laboratory for Physical Science in Burlington, Massachusetts.[5] He designed a pulse-width modulation (PWM) amplifier for audio applications,[8] but it was not successful in the market because there was no power transistor included. He became interested in tuners such as a gyrator and a phase-locked loop (PLL). He was hired by Signetics to develop a PLL IC in 1968. He designed an oscillator for PLLs such that the frequency did not depend on the power supply voltage or temperature. However, Signetics laid off half of its employees, and the development was frozen due to a recession.[9]

Camenzind proposed the development of a universal circuit based on the oscillator for PLLs, and asked that he would develop it alone, borrowing their equipment instead of having his pay cut in half. Other engineers argued the product could be built from existing parts, but the marketing manager bought the idea. Among 5xx numbers that were assigned for analogue ICs, the special number "555" was chosen.[5][9]

Camenzind also taught circuit design at Northeastern University in the morning, and went to the same university at night to get a master's degree in Business Administration.[10] The first design was reviewed in the summer of 1971. There was no problem, so it had gone to the layout design. A few days later, he got the idea of using a direct resistance instead of a constant current source, and found that it worked. The change decreased the required 9 pins to 8, so the IC could be fit in an 8-pin package instead of a 14-pin package. This design passed the second design review, and the prototype was completed in October 1971. Its 9-pin copy had been already released by another company founded by an engineer who attended the first review and retired from Signetics, but they withdrew it soon after the 555 was released. The 555 timer was manufactured by 12 companies in 1972 and it became the best selling product.[9]

Part name[edit]

It has been falsely hypothesized that the 555 got its name from the three 5  resistors used within,[11] but Hans Camenzind has stated that the part number was arbitrary,[5] thus it's just a coincidence they matched. The "NE" and "SE" letters of the original parts numbers (NE555 and SE555) were temperature designations for analog chips from Signetics, where "NE" was commercial temperature range and "SE" was military temperature range.

Design[edit]

Depending on the manufacturer, the standard 555 package includes 25 transistors, 2 diodes and 15 resistors on a silicon chip installed in an 8-pin dual in-line package (DIP-8).[12] Variants available include the 556 (a 14-pin DIP combining two complete 555s on one chip),[13] and 558 / 559 (both a 16-pin DIP combining four reduced-functionality timers on one chip).[2]

The NE555 parts were commercial temperature range, 0 °C to +70 °C, and the SE555 part number designated the military temperature range, −55 °C to +125 °C. These were available in both high-reliability metal can (T package) and inexpensive epoxy plastic (V package) packages. Thus the full part numbers were NE555V, NE555T, SE555V, and SE555T.

Low-power CMOS versions of the 555 are also available, such as the Intersil ICM7555 and Texas Instruments LMC555, TLC555, TLC551.[14][15] [16][17] CMOS timers use significantly less power than bipolar timers, also CMOS timers cause less supply noise than bipolar version when the output switches states. The ICM7555 datasheet claims that it usually doesn't require a "control" capacitor and in many cases does not require a decoupling capacitor across the power supply pins. For good design practices, a decoupling capacitor should be included, however, because noise produced by the timer or variation in power supply voltage might interfere with other parts of a circuit or influence its threshold voltages.

Internal schematic[edit]

The internal block diagram and schematic of the 555 timer are highlighted with the same color across all three drawings to clarify how the chip is implemented:[2]

  • Green - Between the positive supply voltage VCC and the ground GND is a voltage divider consisting of three identical resistors which create two reference voltages at 13 VCC and 23 VCC. The latter is connected to the "Control Voltage" pin. All three resistors have the same resistance, 5 kΩ for bipolar timers, 40 kΩ (or other higher resistance values) for CMOS timers. It is a false myth that the 555 IC got its name from these three 5 kΩ resistors.[5]
  • Yellow - The comparator negative input is connected to the higher-reference voltage divider of 23 VCC (and "Control" pin), and comparator positive input is connected to the "Threshold" pin.
  • Orange - The comparator positive input is connected to the lower-reference voltage divider of 13 VCC, and comparator negative input is connected to the "Trigger" pin.
  • Purple - A SR flip-flop stores the state of the timer and is controlled by the two comparators. The "Reset" pin overrides the other two inputs, thus the flip-flop (and therefore the entire timer) can be reset at any time.
  • Pink - The output of the flip-flop is followed by an output stage with push-pull (P.P.) output drivers that can load the "Output" pin with up to 200 mA (varies by device).
  • Cyan- Also, the output of the flip-flop turns on a transistor which connects the "Discharge" pin to ground.
555 internal block diagram[1]
555 internal schematic of bipolar version
555 internal schematic of CMOS version

Pinout[edit]

The typical pinout of the 555 and 556 IC packages are as follows:[2][1][18]

555 Pin# 556 Pin# Pin Name Pin Purpose[2]
1 7 GND Ground supply - ground reference voltage (zero volts).
2 6, 8 TRIG Trigger - the OUT pin goes high and a timing interval starts when this input falls below 12 of CTRL voltage (which is typically 13 VCC, CTRL being 23 VCC by default if CTRL is left open). More simply we can say that OUT will be high as long as the trigger is kept at low voltage. Output of the timer totally depends upon the amplitude of the external trigger voltage applied to this pin.
3 5,9 OUT Output - the push-pull (P.P.) output is driven to GND or approximately 1.7 V below +VCC. (Note: CMOS timer parts can drive output up to VCC rail.) Signetics recommends a 1 nF bypass capacitor be connected at the output pin in circuits that connect to digital logic inputs, which may help minimize 555 output switching noise from causing problems.[2]
4 4,10 RESET Reset - a timing interval may be reset by driving this input to GND, but the timing does not begin again until RESET rises above approximately 0.7 volts. Overrides TRIG which overrides THR. (THR instead overrides TRIG on the LM555)
5 3,11 CTRL Control (or Control Voltage or CV) - provides "control" access to the internal voltage divider (by default is 23 VCC). By applying a voltage to the CONTROL VOLTAGE input one can alter the timing characteristics of the device. In most applications, this pin is not used, thus it's recommended to connect a low-noise 10 nF bypass capacitor (film or C0G ceramic) between Control pin and Ground pin to filter noise on the higher reference voltage.[2] The control pin input can be used to build an astable multivibrator with a frequency-modulated output.
6 2,12 THR Threshold - the timing (OUT high) interval ends when the voltage at THR ("threshold") is greater than that at CTRL (23 VCC if CTRL is open). Overrides TRIG on the LM555
7 1,13 DIS Discharge - open-collector output which may discharge a capacitor between intervals. In phase with output.
8 14 VCC Positive supply - the guaranteed voltage range of bipolar parts are typically 4.5 volt to 15 volts (some parts rated up to 16 volts or 18 volts), though most bipolar parts will operate at voltages as low as 3 volts. (Note: CMOS timer parts have a lower minimum voltage rating.) It's recommended that a 100 nF bypass capacitor be connected as close as possible to this pin,[2] and optionally a 10 to 100 uF reservoir capacitor depending on the size of the load on the output pin. These capacitance values are a starting point for consideration instead of mandatory values that must be used.
Pinout diagram of 555 single timer
(8 pins)[1][2]
Pinout diagram of 556 dual timer
(14 pins) (conceptually two 555 timers)[18][2]

Modes[edit]

The IC 555 has three operating modes:

  1. Astable (free-running) mode – the 555 can operate as an electronic oscillator. Uses include LED and lamp flashers, pulse generation, logic clocks, tone generation, security alarms, pulse position modulation and so on. The 555 can be used as a simple ADC, converting an analog value to a pulse length (e.g., selecting a thermistor as timing resistor allows the use of the 555 in a temperature sensor and the period of the output pulse is determined by the temperature). The use of a microprocessor-based circuit can then convert the pulse period to temperature, linearize it and even provide calibration means.
  2. Monostable mode – in this mode, the 555 functions as a "one-shot" pulse generator. Applications include timers, missing pulse detection, bounce-free switches, touch switches, frequency divider, capacitance measurement, pulse-width modulation (PWM) and so on.
  3. Bistable (schmitt trigger) mode – the 555 can operate as a flip-flop, if the DIS pin is not connected and no capacitor is used. Uses include bounce-free latched switches.

Astable[edit]

Schematic of a 555 in astable mode
Waveform in astable mode (french)

In 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:

[19]

The high time from each pulse is given by:

and the low time from each pulse is given by:

where R1 and R2 are the values of the resistors in ohms and C is the value of the capacitor in farads.

The power capability of R1 must be greater than .

Particularly with bipolar 555s, low values of must be avoided so that the output stays saturated near zero volts during discharge, as assumed by the above equation. Otherwise the output low time will be greater than calculated above. The first cycle will take appreciably longer than the calculated time, as the capacitor must charge from 0V to 23 of VCC from power-up, but only from 13 of VCC to 23 of VCC on subsequent cycles.

To have an output high time shorter than the low time (i.e., a duty cycle less than 50%) a small diode (that is fast enough for the application) can be placed in parallel with R2, with the cathode on the capacitor side. This bypasses R2 during the high part of the cycle so that the high interval depends only on R1 and C, with an adjustment based the voltage drop across the diode. The voltage drop across the diode slows charging on the capacitor so that the high time is a longer than the expected and often-cited ln(2)*R1C = 0.693 R1C. The low time will be the same as above, 0.693 R2C. With the bypass diode, the high time is

where Vdiode is when the diode's "on" current is 12 of Vcc/R1 which can be determined from its datasheet or by testing. As an extreme example, when Vcc= 5 and Vdiode= 0.7, high time = 1.00 R1C which is 45% longer than the "expected" 0.693 R1C. At the other extreme, when Vcc= 15 and Vdiode= 0.3, the high time = 0.725 R1C which is closer to the expected 0.693 R1C. The equation reduces to the expected 0.693 R1C if Vdiode= 0.

The operation of RESET in this mode is not well-defined. Some manufacturers' parts will hold the output state to what it was when RESET is taken low, others will send the output either high or low.

The astable configuration, with two resistors, cannot produce a 50% duty cycle. To produce a 50% duty cycle, eliminate R1, disconnect pin 7 and connect the supply end of R2 to pin 3, the output pin. This circuit is similar to using an inverter gate as an oscillator, but with fewer components than the astable configuration, and a much higher power output than a TTL or CMOS gate. The duty cycle for either the 555 or inverter-gate timer will not be precisely 50% and will change based off any load that the output is also driving while high (longer duty cycles for greater loads) due to the fact the timing network is supplied from the devices output pin, which has different internal resistances depending on whether it is in the high or low state (high side drivers tend to be more resistive).

Monostable[edit]

Schematic of a 555 in monostable mode
Waveform in monostable mode

In monostable mode, the output pulse ends when the voltage on the capacitor equals 23 of the supply voltage. The output pulse width can be lengthened or shortened to the need of the specific application by adjusting the values of R and C.[20]

The output pulse width of time t, which is the time it takes to charge C to 23 of the supply voltage, is given by

where t is in seconds, R is in ohms (resistance) and C is in farads (capacitance).

While using the timer IC in monostable mode, the main disadvantage is that the time span between any two triggering pulses must be greater than the RC time constant.[21] Conversely, ignoring closely spaced pulses is done by setting the RC time constant to be larger than the span between spurious triggers. (Example: ignoring switch contact bouncing.)

Bistable[edit]

Schematic of a 555 in bistable mode
A noisy signal (U) fed into a comparator (A) and a Schmitt trigger (B). The green dotted lines are the circuit's switching thresholds.

In bistable mode, the 555 timer acts as a basic flip-flop. The trigger and reset inputs (pins 2 and 4 respectively on a 555) are held high via pull-up resistors while the threshold input (pin 6) is simply floating. Thus configured, pulling the trigger momentarily to ground acts as a 'set' and transitions the output pin (pin 3) to VCC (high state). Pulling the reset input to ground acts as a 'reset' and transitions the output pin to ground (low state). No timing capacitors are required in a bistable configuration. Pin 7 (discharge) is left unconnected, or may be used as an open-collector output.[22]

A 555 timer can be used to create a schmitt trigger which converts a noisy input into a clean digital output. The input signal should be connected through a series capacitor which then connects to the trigger and threshold pins. A resistor divider, from VCC to GND, is connected to the previous tied pins. The reset pin is tied to VCC.

Specifications[edit]

Texas Instruments NE555 in DIP-8 and SO-8 packages[1]

These specifications apply to the NE555. Other 555 timers can have different specifications depending on the grade (military, medical, etc.). These values should be considered "ball park" values, instead the current official datasheet from the exact manufacturer of each chip should be consulted for parameter limitation recommendations.

Supply voltage (VCC) 4.5 to 15 V
Supply current (VCC = +5 V) 3 to 6 mA
Supply current (VCC = +15 V) 10 to 15 mA
Output current (maximum) 200 mA
Maximum Power dissipation 600 mW
Power consumption (minimum operating) 30 mW@5V, 225 mW@15V
Operating temperature 0 to 75 °C

Packages[edit]

In 1972, Signetics originally released the 555 timer in 8-pin DIP and 8-pin TO-5 metal can packages, and the 556 timer was released in 14-pin DIP package.[4]

Currently, the 555 is available in through-hole packages as DIP-8 and SIP-8 (both 2.54mm pitch),[23] and surface-mount packages as SO-8 (1.27mm pitch), SSOP-8 / TSSOP-8 / VSSOP-8 (0.65mm pitch), BGA (0.5mm pitch).[1] The Microchip Technology MIC1555 is a 555 CMOS timer with 3 fewer pins available in SOT23-5 (0.95mm pitch) surface mount package.[24]

Derivatives[edit]

Numerous companies have manufactured one or more variants of the 555, 556, 558 timers over the past decades as many different part numbers. The following is a partial list: AMD, California Eastern Labs, CEMI, Custom Silicon Solutions, Diodes Inc, ECG Philips, Estek, Exar, Fairchild, Gemini, GoldStar, Harris, HFO, Hitachi, IK Semicon, Intersil, JRC, Lithic Systems, Maxim, Micrel, MOS, Motorola, ON, Microchip, National, NEC, NTE Sylvania, NXP, Philips, Raytheon, RCA, Renesas, Sanyo, Signetics, Silicon General, Solid State Scientific, STMicroelectronics, Teledyne, TI, Unisonic, Wing Shing, X-REL, Zetex.

Manufacturer Part
Number
Production
Active
IC
Process
Timer
Total
Supply
Min (Volt)
Supply
Max (Volt)
5V Supply
Iq (μA)
Frequency
Max (MHz)
Remark Datasheet
Custom Silicon Solutions CSS555 Yes CMOS 1 1.2 5.5 4.3 1.0 Low Voltage, Lowest Current
Internal EEPROM configuration

[25] [26]

Diodes Incorporated ZSCT155 No CMOS 1 0.9 6 150 0.33 Lowest supply voltage

[27]

Intersil ICM7555 Yes CMOS 1 2 18 40 1.0 Lowest current of common parts

[14]

Intersil ICM7556 Yes CMOS 2 2 18 80 1.0 Lowest current of common parts

[14]

Japan Radio Company NJM555 Yes Bipolar 1 4.5 16 3000 0.1* SIP-8 package

[23]

Microchip Technology MIC1555 Yes CMOS 1* 2.7 18 240 5.0* SOT-23-5 package

[24]

ON Semiconductor LM555 Yes Bipolar 1 4.5 16 3000 0.1*

[28]

Signetics NE555 No Bipolar 1 4.5 16 3000 0.1* First 555 timer
DIP-8 and TO-5-8 package

[4] [13] [29] [2]

Signetics NE556 No Bipolar 2 4.5 16 6000 0.1* First 556 timer
DIP-14 package

[13][2]

Signetics NE558 No Bipolar 4* 4.5 18 4800* 0.1* First 558 timer
DIP-16 package

[2]

Texas Instruments LM555 Yes Bipolar 1 4.5 18 3000 0.1*

[21]

Texas Instruments LM556 Yes Bipolar 2 4.5 16 6000 0.1*

[30]

Texas Instruments LMC555 Yes LinCMOS 1 1.5 15 100 3.0 DSBGA-8 package (smallest 555)

[15]

Texas Instruments NE555 Yes Bipolar 1 4.5 16 3000 0.1* Similar to Signetic NE555

[1]

Texas Instruments NE556 Yes Bipolar 2 4.5 16 6000 0.1* Similar to Signetic NE556

[18]

Texas Instruments TLC551 Yes LinCMOS 1 1 15 170 1.8 Lowest voltage of active parts

[17]

Texas Instruments TLC552 Yes LinCMOS 2 1 18 340 2.8 Lowest voltage of active parts

[31]

Texas Instruments TLC555 Yes LinCMOS 1 2 15 170 2.1

[16]

Texas Instruments TLC556 Yes LinCMOS 2 2 15 340 2.1

[32]

X-REL Semiconductor XTR655 Yes 1 2.8 5.5 170 4.0 Extreme temp (-60°C to +230°C)

[33]

Die of a NE556 dual timer manufactured by STMicroelectronics.
Die of a NE558D quad timer manufactured by Signetics.
Table notes
  • All information in the above table was pulled from references in the datasheet column, except where denoted below.
  • For "Timer Total" column, a "*" denotes parts that are missing 555 timer features.
  • For "Iq" column, a 5 volt supply was chosen as a common voltage to make it easier to compare. The value for Signetics NE558 is an estimate, because NE558 datasheets don't state Iq at 5V.[2] The value listed in this table was estimated by comparing the 5V to 15V ratio of other bipolar datasheets, then derating the 15V parameter for the NE558 part, which is denoted by the "*".
  • For "Frequency Max" column, a "*" denotes values that may not be the actual maximum frequency limit of the part. The MIC1555 datasheet discusses limitations from 1 to 5 MHz.[24] Though most bipolar timers don't state the maximum frequency in their datasheets, they all have a maximum frequency limitation of hundreds of KHz across their full temperature range. Section 8.1 of the Texas Instruments NE555 datasheet[1] states a value of 100 KHz, and their website shows a value of 100 KHz in timer comparison tables, which is overly conservative. In Signetics App Note 170, states that most devices will oscillate up to 1 MHz, however when considering temperature stability it should be limited to about 500 KHz.[2]
Table manufacturer notes

Over the years, numerous IC companies have merged. The new parent company inherits everything from the previous company then datasheets and chip logos are changed over a period of time to the new company. This information is useful when tracking down datasheets for older parts. Instead of including every related company in the above table, only one name is listed, and the following list can be used to determine the relationship.

556 dual timer[edit]

The dual version is called 556. It features two complete 555s in a 14 pin package. Only the two power supply pins are shared between the two timers.[13] Bipolar version are currently available, such as the NE556 and LM556.[18][30] CMOS versions are currently available, such as the Intersil ICM7556 and Texas Instruments TLC556 and TLC552.[14][32][31]

558 quad timer[edit]

Pinout diagram of 558 quad timer
(16 pins) The 558 timers are different than 555 timer (obsolete part)[2]

The quad version is called 558. It has four reduced-functionality timers in a 16 pin package (four complete 555 timer circuits would've required 26 pins).[2] Since the 558 is uniquely different than the 555 and 556, the 558 wasn't as popular. Currently the 558 is not manufactured by any major chip companies (possibly not by any companies), thus the 558 should be treated as obsolete. Parts are still available from a limited number of sellers as "new old stock" (N.O.S.).[34]

Partial list of differences between 558 and 555 chips:[2]

  • One VCC and one GND, similar to 556 chip.
  • Four "Reset" are tied together internally to one external pin (558).
  • Four "Control Voltage" are tied together internally to one external pin (558).
  • Four "Triggers" are falling-edge sensitive (558), instead of level sensitive (555).
  • Two resistors in the voltage divider (558), instead of three resistors (555). One comparator (558), instead of two comparators (555).
  • Four "Output" are open-collector (O.C.) type (558), instead of push-pull (P.P.) type (555). Since the 558 outputs are open-collector, pull-up resistors are required to "pull up" the output to the positive voltage rail when the output is in a high state. This also means the high state won't be able to source as much current as the low state.

Example applications[edit]

Joystick and game paddles[edit]

IBM PC Game Control Adapter[35]
(8-bit ISA card)

The Apple II microcomputer used a quad timer 558 in monostable (or "one-shot") mode to interface up to four "game paddles" or two joysticks to the host computer.[36] It also used a single 555 for flashing the display cursor.[37]

The original IBM PC used a similar circuit for the game port on the "Game Control Adapter" 8-bit ISA card (IBM part number 1501300).[35][38] In this joystick interface circuit, the capacitor of the RC network (see Monostable Mode above) was generally a 10 nF capacitor to ground with a series 2.2 KΩ resistor to the game port connector.[35] The external joystick was plugged into the adapter card. Internally it had two potentiometers (100 to 150 KΩ each), one for X and other for Y direction. The center wiper pin of the pot was connected to an Axis wire in the cord and one end of the pot was connected to the 5 Volt wire in the cord. The joystick potentiometer acted as a variable resistor in the RC network.[38] By moving the joystick, the resistance of the joystick increased from a small value up to about 100 kΩ.[38][38]

Software running in the IBM PC computer started the process of determining the joystick position by writing to a special address (ISA bus I/O address 201h).[35][38][39] This would result in a trigger signal to the quad timer, which would cause the capacitor 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 capacitor to charge up to 23 of 5 V (or about 3.33 V), which was in turn determined by the joystick position.[38][39] The software then 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.[38]

Stepped tone generator[edit]

See also[edit]

References[edit]

  1. ^ a b c d e f g h "NE555 Datasheet" (PDF). Texas Instruments. September 2014. Archived from the original (PDF) on June 28, 2017. Retrieved June 28, 2017. 
  2. ^ a b c d e f g h i j k l m n o p q r "Linear LSI Data and Applications Manual". Signetics. 1985. Archived from the original (PDF) on April 5, 2016. Retrieved June 29, 2017. (see 555/556/558 datasheets and AN170/AN171 appnotes) 
  3. ^ a b Fuller, Brian (15 August 2012). "Hans Camenzind, 555 timer inventor, dies". EE Times. Retrieved 27 December 2016. 
  4. ^ a b c "Linear Vol1 Databook". Signetics. 1972. Archived from the original (PDF) on January 9, 2013. Retrieved June 28, 2017. 
  5. ^ a b c d e Ward, Jack (2004). The 555 Timer IC – An Interview with Hans Camenzind. The Semiconductor Museum. Retrieved 2010-04-05
  6. ^ Tony R. Kuphaldt. "Lessons In Electric Circuits: Volume VI - Experiments". Chapter 8.
  7. ^ Albert Lozano. "Introduction to Electronic Integrated Circuits (Chips)"
  8. ^ Camenzind, Hans (11 Feb 1966). "Modulated pulse audio and servo power amplifiers". Solid-State Circuits Conference. Digest of Technical Papers. 1966 IEEE International: 90–91. 
  9. ^ a b c Carmenzind, Hans (2010). Translated by 三宅, 和司. "タイマIC 555 誕生秘話" [The birth of the 555 timer IC]. トランジスタ技術 (Transistor Technology) (in Japanese). CQ出版. 47 (12): 73, 74. ISSN 0040-9413. 
  10. ^ Video interview of Hans Camenzind by Transistor Gijutsu magazine (Japanese subtitled); YouTube.
  11. ^ Scherz, Paul (2000) "Practical Electronics for Inventors", p. 589. McGraw-Hill/TAB Electronics. ISBN 978-0-07-058078-7. Retrieved 2010-04-05.
  12. ^ van Roon, Fig 3 & related text.
  13. ^ a b c d "555/556 Timers Databook". Signetics. 1973. Archived from the original (PDF) on October 4, 2012. Retrieved June 28, 2017. 
  14. ^ a b c d "ICM7555-556 Datasheet" (PDF). Intersil. June 2016. Archived from the original (PDF) on June 29, 2017. Retrieved June 29, 2017. 
  15. ^ a b "LMC555 Datasheet" (PDF). Texas Instruments. July 2016. Archived from the original (PDF) on June 28, 2017. Retrieved June 28, 2017. 
  16. ^ a b "TLC555 Datasheet" (PDF). Texas Instruments. August 2016. Archived from the original (PDF) on June 28, 2017. Retrieved June 28, 2017. 
  17. ^ a b "TLC551 Datasheet" (PDF). Texas Instruments. September 1997. Archived from the original (PDF) on June 29, 2017. Retrieved June 29, 2017. 
  18. ^ a b c d "NE556 Datasheet" (PDF). Texas Instruments. June 2006. Archived from the original (PDF) on June 28, 2017. Retrieved June 28, 2017. 
  19. ^ van Roon Chapter: "Astable operation".
  20. ^ van Roon, Chapter "Monostable Mode". (Using the 555 timer as a logic clock)
  21. ^ a b "LM555 Datasheet" (PDF). Texas Instruments. January 2015. Archived from the original (PDF) on June 28, 2017. Retrieved June 28, 2017. 
  22. ^ 555 Timer Operating Modes; 555-timer-circuits.com
  23. ^ a b "NJM555 Datasheet" (PDF). Japan Radio Company. November 2012. Archived from the original (PDF) on June 29, 2017. Retrieved June 29, 2017. 
  24. ^ a b c "MIC1555 Datasheet" (PDF). Microchip Technology. March 2017. Retrieved June 29, 2017. 
  25. ^ "CSS555 Datasheet" (PDF). Custom Silicon Solutions. July 2012. Archived from the original (PDF) on June 29, 2017. Retrieved June 29, 2017. 
  26. ^ "CSS555 Part Search". Jameco Electronics. Retrieved June 30, 2017. 
  27. ^ "ZSCT1555 Datasheet" (PDF). Diodes Incorporated. July 2006. Archived from the original (PDF) on June 29, 2017. Retrieved June 29, 2017. 
  28. ^ "LM555 Datasheet" (PDF). ON Semiconductor. January 2013. Archived from the original (PDF) on June 29, 2017. Retrieved June 29, 2017. 
  29. ^ "Analog Applications Manual". Signetics. 1979. Archived from the original (PDF) on January 9, 2013. Retrieved June 28, 2017. (see chapter 6) 
  30. ^ a b "LM556 Datasheet" (PDF). Texas Instruments. October 2015. Archived from the original (PDF) on June 29, 2017. Retrieved June 29, 2017. 
  31. ^ a b "TLC552 Datasheet" (PDF). Texas Instruments. May 1988. Archived from the original (PDF) on June 29, 2017. Retrieved June 29, 2017. 
  32. ^ a b "TLC556 Datasheet" (PDF). Texas Instruments. September 1997. Archived from the original (PDF) on June 29, 2017. Retrieved June 29, 2017. 
  33. ^ "XTR655 Datasheet" (PDF). X-REL Semiconductor. September 2013. Archived from the original (PDF) on June 29, 2017. Retrieved June 29, 2017. 
  34. ^ NE558 Stock Search; Octopart.
  35. ^ a b c d Game Control Adapter Manual and Schematic (PDF). IBM. Retrieved June 30, 2017. 
  36. ^ "Joysticks, Paddles, Buttons, and Game Port Extenders for Apple II, Atari 400/800, Commodore VIC-20". Creative Computing Video & Arcade Games. 1 (1): 106. Spring 1983. Retrieved June 30, 2017. 
  37. ^ Apple II Reference Manual and Schematics (PDF). Apple Inc. January 1978. Retrieved June 30, 2017. 
  38. ^ a b c d e f g "PC Analog Joystick Interface". epanorama.net. Retrieved June 30, 2017. 
  39. ^ a b Eggebrecht, Lewis C. (1983). Interfacing to the IBM Personal Computer (1st ed.). Sams Publishing. pp. 197–199. ISBN 978-0-672-22027-2. 

Further reading[edit]

Books
Applications Manuals
Datasheets
  • see links in Derivatives and Reference sections of this article

External links[edit]

Calculators
Simulators