Schmitt triggers are comparator circuits that use a signal voltage and hysteresis (a range of voltage where the output stays in the last state it was put into) to determine the output state. The output switches more solidly high or low than just a simple comparator.
- Thresholds (2 of them): The voltage points needed to be reached, in order to change the output.
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Notice how the LED naturally wants to be on. When it is off, that means that the transistor next to it is conducting enough to drop the voltage below the LED’s forward voltage.
The transistor next to the LED normally wants to conduct because of the pull up resistor at it’s base. To turn it off, the transistor closer to the trimpot has to be conducting as that will lower the base voltage.
- 555 Timer IC This 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
- 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
- NPN BJT current source – Bipolar Junction Transistor – 2N3904
- PNP BJT current source – Bipolar Junction Transistor – 2N3906