Thread: help me on my sensor circuit please :)

im to design a sensor circuit that cuts off my toy car's motor power if an obsticale is detected.

when and object is detected, sensor's output voltage rises, thus the comparator gives a high output.

after these steps, im stuck.. i cant seem to get the relay to work. is it the resistor before the transistor or the transistor itself is wrong?

please click on the picture to get a better view ^^



thank youuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuu!

When you say you can't get the relay to work.. Is the relay always on (motor is running) or is it always off?

its kind of like a solar toy car that stops when an object is detected in front of it. to avoid collision.

im using a digital oscilloscope to measure the voltage at each point.

the voltage of the points i measured before the resistor is correct. as in, when i put a piece of paper in front of the sensor, the output goes high, 4.7V in my case.

im just not very sure about why the resister ( i boxed it in purple ) is there & what it is used for. after the resistor, the right half of the circuit, i dont quite understand them.

for your question, if i keep shining light onto the solar panel. then i can say it will be in a "always on" state. until it detects the obsticale, then the relay will "open circuit" the motor's connection. to make the car stop.

thanks ^^ once again

My question was, what is it doing now, not what it is supposed to do.

I don't have a lot of experience with comparators, but I think you would select the resistor to give you an appropriate base current to turn on the transistor based on the comparator output voltage when the comparator output is high.

I'm a little confused by that circuit. If the IR sensor is high, and the comparator output is high, it looks like that would turn on the transistor, which would pick up the relay, which would start the motor, and you want it to stop. Unless you are actually using the normally closed contact of the relay instead of the normally open contact as shown.