Hi there,

i want to ask you how can i connect a smoke detector who is giving me an output voltage of 2.20V to 2.50V (which is not constant) when it detect smoke and 0V when it doesn't detect smoke.

for the PIC16F877A, i need a constant voltage of either 0V or 5V

Can anyone help me with this problem, PLEASE !

If the output from the smoke detector normally drives the sounder then it is probably a square wave of amplitude 5V that your meter is showing as 2.5 as it's only on half the time.

If it isn't a square wave and is a constant 2.5V then a transistor will do the job.

The signal to the pic will be inverted but that can be fixed in software.

Mike.

yeah i am taking the output voltage of the buzzer, the thing i don't want the buzzer to go off when it detects the smoke, only to give input the PIC

the problem is i can't test the sensor inside the laboratory because of the smoke detectors in the lab. so i checked tht outside the laboratory with a digital voltmeter so i am not sure if its a square wave or not, but the voltage was not constant,

plus the buzzer have three wires, one is black, the second one is red and the third one is white, so i believe the black is for ground, red for positive and the white is for the signal, where should i measure the voltage across ground and positive supply or the signal ???