Astable mode 555 timers keep changing the output between high and low in an endless cycle as long as power is applied. The speed of which it does so depends on the value of the timing capacitor and 2 resistors.
Process described here is illustrated below.
- When power is first applied. The output is high and the capacitor charges through one resistor (Vcc to pin 7) and either a diode or another resistor. The LED is on when the output is high because the output is at as close to the positive supply voltage as the output can provide while the other side of the LED in the circuit shown above is at 0V.
- When the capacitor charges to 2/3 of the supply voltage as detected by pin 6 (threshold), then the output goes low (the LED turns off due to both sides of it being at 0 volts) and the capacitor starts discharging through the resistor and then through pin 7 (discharge) to ground. Any current from the supply voltage through the resistor to pin 7 also goes to ground through the IC. So, it doesn’t affect the capacitor discharging at all.
- After the capacitor discharges to 1/3 of the supply voltage as detected by pin 2 (trigger), the output goes high and the capacitor starts charging again.
- Cycle keeps repeating.
- Threshold pin (6) senses when the capacitor reaches 2/3 supply voltage
- Trigger pin (2) senses when the capacitor reaches 1/3 supply voltage.
- Discharge pin (7) discharges the capacitor through the 6-7 resistor, while also sending the Vcc to pin 7 current to ground.
- Output pin (3) can source current as shown in the diagram above, or sink current, where the load comes from Vcc and current sinks into the output when it is low (0V)
White version of the oscilloscope that I use in many of my recent videos.
Power supply I use in my videos.
- 555 Timer IC The particulars of this integrated circuit covered on this page make a lot more sense after you study the basic circuits that follow.
- 555 timer bistable mode – Flip flip basic circuit
- 555 timer monostable mode – One shot
- 555 timer astable multivibrator mode – Flashing LEDs
- 555 timer schmitt trigger logic inverter – NOT gate
- 555 timer LDR controlled astable multivibrator mode LED flasher circuit
- 555 timer – Buzzer output – Astable multivibrator mode – Light dependent resistor LDR controlled circuit
- Electronic component appearance and schematics – Commonly used through hole versions
- Electronic circuit basics
- Voltage sources for electronics basics
- Multimeter measuring voltage
- Resistor component – Learning electronics resistors
- Light Emitting Diodes – Indicator LEDs
- LED circuit -Lighting a Light Emitting Diode
- Resistor limiting current – Ohms law
- Multimeter measuring current
- Wattage – Electrical Power unit
- Resistors connected in parallel
- Series resistors
- Voltage divider – Setting a fractional voltage
- Resistor color code
- Diode – Rectifier
- Trimpot – Trimmer potentiometer – Voltage divider – Variable resistor
- Capacitor component
- Capacitor RC time constant
- Voltage ramp Demonstrated using a capacitor.
- LM334 three terminal adjustable current source not a common component. I use for an easy current source in many circuits.
- Switch NOT logic gate – digital signal inverter
- Switch OR gate – LED circuit
- Switch AND gate – LED circuit
- Switch based NAND logic gate – LED demonstration circuit
Transistors will probably be the most challenging components to learn. Understanding them will help you understand all of electronics much better, and help you the most in being creative while designing your own circuits.
- NPN BJT switch circuit – Bipolar Junction Transistor – 2N3904
- PNP BJT switch – Bipolar Junction Transistor – 2N3906
- NPN BJT emitter follower circuit – transferring a voltage minus a diode drop
- PNP BJT emitter follower circuit – Transferring weak signal voltage with a diode voltage shift
- Bipolar Junction Transistor BJT voltage follower circuit improved to eliminate base emitter diode shift
- NPN BJT current source – Bipolar Junction Transistor – 2N3904
- PNP BJT current source – Bipolar Junction Transistor – 2N3906
- Schmitt trigger – NPN BJT
- Zener diode component – voltage reference – regulator
- Voltage doubler circuit fragment- Capacitor charge pump – Some V loss
- 7805 5V positive voltage regulator IC
- Battery voltage state of charge SOC – From fully charged to discharged
These pages are still being compiled.