Liquid or Air Pressure Switch with Relay
This pressure switch project is built using a piezoresistive transducer, LM358 OPAMP as comparator, and a relay. The circuit activate the relay when the pressure in a system exceed a given set-point. Basically, this switch can power ON or OFF a pump, valve, motor, when certain pressure is reached. A trimmer potentiometer is provided to set the trigger point. LM358 is used as comparator, relay has Normally Open/Normally closed contacts with current rating 5Amps @ 230V AC or 10Amps @ 28V DC. LM78L05 IC is used to provide 5V DC supply to pressure sensor. The operating voltage of this circuit is 12V and it consumes approx. 40mA current when Relay is in ON condition. We have used MPXV5010DP pressure sensor from NXP. This is an analog pressure sensor and the output of this sensor is 0.2V to 4.7V which is proportional to the applied pressure range of 0-10kPa (0 to 1.75PSI).
Liquid or Air Pressure Switch with Relay – [Link]