The most logical device to use as a schmitt trigger is
the opamp.
**broken link removed**
The output current of most opamps is a bit too low to
drive the "average" relay, that's where the BJT comes
in play. The opamp drives the BJT and the BJT drives
the relay.
And the relay drives the load, this load can be almost
anything, light bulbs, a motor, a heater . . .
In this case it's only a led.
I think you should put a bit more effort in your work
otherwise you'll become as lazy and as stupid as I am.
You wouldn't want that to happen don't you ?
Only one BJT, one OPAMP UA741 and a single power supply of 12V must be used.
For this project, the relay can be substituted by a light emitting diode (LED), that is, when the relay is on, the LED will light up.
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He left out the series resistor for the LED, unless he is depending on the 741 output to limit the LED current.
A relay suppressor diode may not be needed here.