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For more data on the 555, see these pages:
555-Page 1 for CD users: 555-Page 1
555-Page 2 555-Page 2
555-Page 3 555-Page 3
555-Test 555-Test
For a list of every electronic symbol, see: Circuit Symbols. For more articles and projects to suit the hobbyist: see TALKING ELECTRONICS WEBSITE
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54 CIRCUITS as of 29-11-2009 Rev1.2 29-11-2009 - added Hysteresis (Schmitt Trigger, Knight Rider-2, Morse Code,
Music Box, Reaction Timer Game 61 CIRCUITS as of 5-12-2009 Rev1.3 5-12-2009 - added Traffic Lights, Driving White LEDs, TV Remote Control Jammer, 3x3x3 Cube, Up/Down Fading LED, H-Bridge, H-Bridge with PWM. 64 CIRCUITS as of 14-12-2009 Bike Turning Signal, 555 on 24v, Police Lights, LED Dice, Roulette, Model Railway Time 71 CIRCUITS as of 1-1-2010 plus: Servo Controller, Curtain Closer, Stepper Motor Controller, 4-way Traffic Lights, TE555-1 Chip: Stepper Motor Controller, 76 CIRCUITS as of 10-1-2010 plus: Useless Machine, Animated Display, 4 Alarm Sounds, Police Lights-3, Dice to 7-Segment Display LED FX See TALKING ELECTRONICS WEBSITE email Colin Mitchell: talking@tpg.com.au
INTRODUCTION
This e-book covers the 555.
The 555 is everywhere and it is one of the cheapest and most-rugged chips on the market. It comes as a TTL 555 and will operate from 4v to about 16-18v. It costs from 20 cents (eBay) to $1. depending on the quantity and distributor. The circuitry inside the chip takes about 10mA - even when the output is not driving a load. This means it is not suitable for battery operation if the chip is to be powered ALL THE TIME. The 555 is also available as a CMOS chip (ICM7555 or ICL7555 or TLC555) and will operate from 2v to 18v and takes 60uA when the circuitry inside the chip is powered. The "7555" costs from 60 cents (eBay) to $2. We call the TTL version "555" and the CMOS version "7555." This is called ELECTRONICS JARGON. The 555 comes as a single timer in an 8-pin package or a dual timer (556) in a 14 pin package. The 7555 comes as a single timer in an 8-pin package or a dual timer (7556) in a 14 pin package. The 555 and 7555 are called TIMERS or Timer Chips. They contain about 28 transistors and the only extra components you need are called TIMING COMPONENTS. This is an external resistor and
following four pages: 555-Page 1 555-Page 2 555-Page 3 555-Test Many of the circuits have been designed by Colin Mitchell: Music Box, Reaction Timer Game, Traffic Lights, TV Remote Control Jammer, 3x3x3 Cube, while others are freely available on the web. But this eBook has brought everything together and covers just about every novel 555 circuit. If you think you know everything about the 555, take the 555-Test and you will be surprised!
SI NOTATION
All the schematics in this eBook have components that are labelled using the System International (SI) notation system. The SI system is an easy way to show values without the need for a decimal point. Sometimes the decimal point is difficult to see and the SI system overcomes this problem and offers a clear advantage. Resistor values are in ohms (R), and the multipliers are: k for kilo, M for Mega. Capacitance is measured in farads (F) and the sub-multiples are u for micro, n for nano, and p for pico. Inductors are measured in Henrys (H) and the sub-multiples are mH for milliHenry and uH for microHenry. A 10 ohm resistor would be written as 10R and a 0.001u capacitor as 1n. The markings on components are written slightly differently to the way they are shown on a circuit diagram (such as 100p on a circuit and 101 on the capacitor) and you will have to look on the internet under Basic Electronics to learn about these differences.
NEW! FROM
TALKING
ELECTRONICS
A new range of 555 chips have been designed by Talking Electronics to carry out tasks that normally need 2 or more chips. These chips are designated: TE 555-1, TE555-2 and the first project to use the TE 555-1 is STEPPER MOTOR CONTROLLER TE555-1. It's a revolutionary concept. Instead of using an old 8- pin TTL 555 chip, you can use a new TE555-1,2,3 8-pin chip and save board space as well as components.
These new chips require considerably less external componentry and the possibilities are endless. Depending on the circuit, they can have a number of timing and frequency outputs as well as a "power- down" feature that consumes almost no current when the circuit is not operating. See the first project in this series: STEPPER MOTOR CONTROLLER TE555-1. How are your powers of observation? Can you find the LED: SQUARE WAVE OSCILLATOR KIT A Square Wave Oscillator Kit is available from Talking Electronics for under $10.00. See full details of circuit below. (This link will send an email to Colin Mitchell and you will be advised of costs and how to send money via Paypal or credit card.) Or email Colin Mitchell: talking@tpg.com.au 555 KIT A kit of components to make many of the circuits described in this eBook is available for $10.00 plus $7.00 post. Or email Colin Mitchell: talking@tpg.com.au The kit contains the following components: (plus extra 30 resistors and 10 capacitors for experimenting), plus:
Curtain Closer
Dark Detector
Dice
Dice to 7-Segment Display
Display - Animated
Driving A Bi-Coloured LED
Driving A Relay
Driving White LEDs
Fading LED
Fastest 555 Oscillator
Flashing Indicators
Flashing Railroad Lights
Flip Flop
Four Alarm Sounds
Function of each 555 pin
H-Bridge
H-Bridge with PWM
Headlight Flasher - faulty circuit
Hee Haw Siren
High Frequency 555 Oscillator
How to use the 555
Hysteresis
Increasing Output Current
Increasing Output Push-Pull
Current
Inverter 12v to 240v
Inside the 555
Kitt Scanner
Knight Rider
Laser Ray Sound
Latch
Latch - using transistors
LED Dice
LED Dimmer
LED FX
Light Controlled Screamer Siren
Light Detector
Lights - Traffic Lights
Low Frequency 555 Oscillator
Machine Gun
Mark-Space Ratio
Memory Cell
Mercury Switch Detector - faulty
circuit
Metal Detector
Missing Pulse Detector - faulty
circuit
Model Railway Time
Screamer Siren - Light
Controlled
Servo Controller
Servo Tester
Simplest 555 Oscillator
Siren 100dB
Square Wave Oscillator
Stepper Motor Controller
Stun Gun
Substituting a 555 - Part 1
Substituting a 555 - Part 2
Switch Debounce
Tachometer
TE555-1 Stepper Motor
Controller
Ticking Bomb
Tilt Switch
Touch Switch
Touch ON-OFF
Toy Organ
Traffic Lights
Traffic Lights - 4 way
Transistor Tester
Trigger Timer - 74c
Turning Signal
TV Remote Control Jammer
Useless Machine
Uneven Clicks
Up/Down Fading LED
Using the 555
VCO
Voltage Doubler
Wailing Siren
Zapper (Dr Clark)
Zener Diode Tester
2 Minute Timer - 74c
3x3x3 Cube
4 Alarm Sounds
4 way Traffic Lights
10 Minute Timer - 74c
12v to 240v Inverter
100dB Siren
555's - a list of substitutes
555 Amplifier
555 Kit of Components
555 Pinout
555 Mistakes (No-No's)
555 on 24v
Monostable 555
Morse Keyer
Mosquito Repeller
Motor Controller (stepper Motor)
Motor PWM
Multivibrator - Astable
Music Box
Negative Voltage
Normally Closed Trigger
One-Shot 555
555 VCO
556 Dual Timer
to Index THE 555 PINS Here is the identification for each pin: When drawing a circuit diagram, always draw the 555 as a building block, as shown below with the pins in the following locations. This will help you instantly recognise the function of each pin:
Pin 1 GROUND. Connects to the 0v rail.
Pin 2 TRIGGER. Detects 1/3 of rail voltage to make output HIGH. Pin 2 has control over pin 6. If pin 2
is LOW, and pin 6 LOW, output goes and stays HIGH. If pin 6 HIGH, and pin 2 goes LOW, output goes LOW while pin 2 LOW. This pin has a very high impedance (about 10M) and will trigger with about 1uA.
Pin 3 OUTPUT. (Pins 3 and 7 are "in phase.") Goes HIGH (about 2v less than rail) and LOW (about
0.5v less than 0v) and will deliver up to 200mA.
Pin 4 RESET. Internally connected HIGH via 100k. Must be taken below 0.8v to reset the chip.
Pin 5 CONTROL. A voltage applied to this pin will vary the timing of the RC network (quite
considerably).
to Index THE FASTEST 555 OSCILLATOR The highest frequency can be obtained by connecting the output to pins 2 and 6. This arrangement takes about 5mA and produces an output as shown: View the output on a CRO. Our 555 "Test Chip" produced a frequency of 300kHz at 5v and 12v. (CMOS versions will operate at a higher frequency.) Note the very short LOW TIME. to Index INSIDE THE 555
Note: Pin 7 is "in phase" with output Pin 3 (both are low at the same time). Pin 7 "shorts" to 0v via a transistor. It is pulled HIGH via R1. Maximum supply voltage 16v - 18v Current consumption approx 10mA Output Current sink @5v = 5 - 50mA @15v = 50mA Output Current source @5v = 100mA @15v = 200mA Maximum operating frequency 300kHz - 500kHz Faults with Chip: Consumes about 10mA when sitting in circuit Output voltage can be up to 2.5v less than rail voltage Output can be 0.5v to 1.5v above ground Sources up to 200mA but sinks only 50mA A NE555 was tested at 1kHz, 12.75v rail and 39R load. The Results: Output voltage 0.5v low, 11.5v high at output current of 180mA The "test chip" performance was excellent. to Index HOW TO USE THE 555 There are many ways to use the 555. They can be used in hundreds of different circuits to do all sorts of clever things. They can also be used as three different types of oscillators.
(a) Astable Multivibrator - constantly oscillates
For frequencies above 1 cycle per second, it is called an oscillator (multivibrator or square wave oscillator).
Suppose R1 = 10k, R2 = 100k and C = 1u Using the formula on the graph, the total resistance = 10 + 100 + 100 = 210k The scales on the graph are logarithmic so that 210k is approximately near the first "0" on the 100k. Draw a line parallel to the lines on the graph and where it crosses the 1u line, is the answer. The result is approx 9Hz. The frequency of an astable circuit can also be worked out from the following formula:
frequency =
(R 1 +2R 2 )×C
555 astable frequencies
C
R 1 =1k R 2 =6k R 1 =10k R 2 =68k R 1 =100k R 2 =680k 0.001μ 100kHz 10kHz 1kHz 0.01μ 10kHz 1kHz 100Hz 0.1μ 1kHz 100Hz 10Hz 1μ 100Hz 10Hz 1Hz 10μ 10Hz 1Hz 0.1Hz to Index HIGH FREQUENCY OSCILLATORS 360kHz is the absolute maximum as the 555 starts to malfunction with irregular bursts of pulses above this frequency. To improve the performance of the oscillator, a 270R and 1n can be added as shown in the second circuit: to Index LOW FREQUENCY OSCILLATORS - called TIMERS
If the capacitor is replaced with an electrolytic, the frequency of oscillation will reduce. When the frequency is less than 1Hz, the oscillator circuit is called a timer or "delay circuit." The 555 will produce delays as long as 30 minutes but with long delays, the timing is not accurate.
555 Delay Times:
C
R 1 =100k
R 2 =100k
R 1 =470k
R 2 =470k
R 1 =1M
R 2 =1M
10μ 2.2sec 10sec 22sec 100 μ 22sec 100sec 220sec 470μ 100sec 500sec 1000sec The following circuits show a 1-5 minute timer and 10 minute timer: to Index
goes HIGH. CIRCUIT OPERATION When the circuit is turned on, the capacitor is uncharged. Pin 6 sees a LOW and pin 2 sees a HIGH. Remember: Pin 2 must be LOW to make the output HIGH. Pin 6 must be HIGH to make the output LOW. Neither pin is "controlling the chip" at start-up and the chip is designed to output a LOW with these start-up conditions. In other words, the chip starts in RESET mode. Pin 7 is LOW and the capacitor does not charge. When pin 2 see a LOW pulse, the chip goes to SET mode and the output goes HIGH. Pin 7 goes OPEN and capacitor C charges via R. When pin 6 sees 2/3 rail voltage, the chip goes to RESET mode with pin 3 and 7 LOW. The capacitor instantly discharges via pin 7 and the circuit waits for a negative pulse on pin 2. to Index THE 555 AS A VOLTAGE CONTROLLED OSCILLATOR (VCO) By adjusting the voltage on pin 5, (the CONTROL pin) the frequency of the oscillator can be adjusted quite considerably. See Police Siren for an application.
to Index THE 555 AS RAMP GENERATOR When a capacitor is charged via a constant current, the waveform across it is a ramp. to Index "No-No's" Here are some mistakes to avoid:
- Pin 7 gets connected to the 0v rail via a transistor inside the chip during part of the operation of the 555. If the pot is turned to very low resistance in the following circuit, a high current will flow through the pot and it will be damaged:
- The impedance of the 100u electrolytic will allow a very high current to flow and the chip will get very hot. Use 10u maximum when using 8R speaker.
- The reset pin (pin 4) is internally tied HIGH via approx 100k but it should
- Don't use high value electrolytics and high resistances to produce long delays. The 555 is very unreliable with timing values above 5-10 minutes. The reason is simple. The charging current for the electrolytic is between 1
- 3 microamp in the following diagram (when the electro is beginning to charge) and drops to less than 1 microamp when the electro is nearly charged. If the leakage of the electro is 1 microamp, it will never fully charge and allow the 555 to "time-out."
- Do not connect a PNP to the output of a 555 as shown in the following diagram. Pin 3 does not rise high enough to turn off the transistor and the current taken by the circuit will be excessive. Use an NPN driver. to Index 555's
Here is a list of 555's from different manufacturers plus the range of low voltage, low current 555's. The normal 555 is called a TTL or Transistor-Transistor-Logic chip and it consumes about 10mA when "sitting and doing nothing." It will work from 4v to 18v. A low current version is available from the list below, (called a CMOS version) and consumes about 10uA to 100uA. Some of these chips work from 1.5v to 15v (ZSCT1555 = 9v max) but they can sink and source only about 100mA (less than 30mA at 2v). The 555 is the cheapest and the others cost about double. The normal 555 oscillates up to 300kHz. A CMOS version can oscillate to 3MHz. You need to know the limitations as well as the advantages of these chips before substituting them for the normal 555:
Manufacturer Model Remark
Custom Silicon Solutions CSS555/CSS555C CMOS from 1.2V, IDD < 5uA ECG Philips ECG955M Exar XR- Fairchild Semiconductor NE555/KA Harris HA IK Semicon ILC555 CMOS from 2V Intersil SE555/NE555/ICM Lithic Systems LC Maxim ICM7555 CMOS from 2V Motorola MC1455/MC National Semiconductor LM1455/LM555/LM555C National Semiconductor LMC555 CMOS from 1.5V NTE Sylvania NTE955M Raytheon RM555/RC RCA CA555/CA555C STMicroelectronics NE555N/ K3T Talking Electronics TE555-1, -2, -3, - email Talking Electronics $2. ea Texas Instruments SN52555/SN72555; TLC555 CMOS from 2V Zetex ZSCT1555 down to 0.9V (9v max) to Index REPLACING A 556 WITH TWO 555's Here is a handy reference to replace a 556 dual timer with two 555's:
