Buzzers are nice for beginning electronics because you can hear when steady current goes through active buzzers, or when current is changing rapidly through passive buzzers. 555 timer works well to keep circuits on/off over a period of time, or to rapidly turn something on/off. Light Dependent resistor make a good variable resistor for changing the output frequency of a 555 timer.
- When power is applied, the capacitor starts charging from the 5V supply through the fixed resistor and the light dependent resistor. At that time the output is also high (as close to the 5V supply that the output can provide. A 1,000µF capacitor is a good value to help keep the active buzzer buzzing for a decent amount of time. A passive buzzer will just make a single click right when the output goes high. So you’d probably want no more than 100µF capacitor for the passive buzzer to speed up the clicks.
- When the capacitor charges to 2/3 of the supply voltage, then the output goes low (a direct connection to 0V ground), and the active buzzer turns off whereas the passive buzzer makes a single click.
- As soon as the capacitor discharges to 1/3 of the supply voltage, then the output goes high and the capacitor charges again. The process repeats as long as power is applied.
- Threshold pin (6) senses when the capacitor is above 2/3 supply voltage.
- Trigger pin (2) senses when the capacitor is below 1/3 supply voltage.
- Discharge pin (7) connects to 0V ground when the output is low. The capacitor discharges through it while it does so, and the current from the supply (5V in this circuit) also goes right to ground, so it doesn’t affect the discharge time. When the output is high, pin 7 basically turns off and no current flows through it. So it doesn’t affect the charging time of the capacitor.
- Light dependent resistor (LDR) and fixed resistor control how much current flows into the capacitor from 5V. The value of the capacitor determines how much current is needed to raise it’s voltage. The capacitor discharges through the LDR alone, so it will discharge anywhere from a little bit to a lot faster than it took to charge. LDRs usually have a lot more resistance than 220Ω, but they can drop well below 220Ω if it is really bright.
- 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.