This circuit is from a 90's documentation. The circuit is simple, as it uses only two transistors, and the control is done by pressure switches. The indication is done by LEDs.
We find this circuit in an American 80's documentation. It makes use of IC sensor which is mounted...
This is a configuration obtained from an old manual, using an operational amplifier of the time....
In the figure we have the way to add hysteresis to an operational amplifier. The relationship...