i need to detect the negative swing of the output of pressure sensor. some info about the signal:
the pressure sensor outputs 2.5VDC at atmospheric (its "gauge" pressure)
vacuum goes from 2.5VDC to 0V, positive pressure goes from 2.5VDC to
5V. the range of the sensor is +/- 15 PSI.i need to detect the peak vacuum voltage, which is somewhere between
2.5VDC and 0V.i am measuring the pressure of a very slow pump, which operates at about 60 rpm, so I get about 1 peak per second.
im thinking an LM339, output connected to cathode of diode, anode of which goes to a cap, which is connected to ground on one side and a momentary "reset" switch that charges up the cap to 2.5V whenever you press it (between measurements)
negative input of 339 goes to the cap voltage positive input of 339 goes to the pressure sensor output
seems to work good in circuit maker
add resistors on output of 339 for pull-up (not really needed i suppose since it only DISCHARGES the cap) , and to limit discharge current into 339 when it trys to pull the cap down
perhaps a 10Meg resistor on cap to 2.5V to pull it up slowly...might not be needed either since you have "Reset" switch which does it instantly
sound good?