Middlesex County, Ontario | Ok, just as I thought. The circuit you drew would always have the buzzer on, you can't just remove the potentiometer the way you did.
The arrow side of the potentiometer goes from 0v-5v as you spin the dial.
The comparator compares the + and - terminals. If + is higher than -, the output goes high. The sensor outputs from 0v-5v, which in reality is more like 0.001v-4.999v.
The way you have drawn the circuit, the - terminal is tied to ground, or 0v. The + terminal (sensor output) is 0.001v-4.999v. 0.001v-4.999v is always higher than 0 volts, therefore the comparator output is always high, and the buzzer is always on.
With the potentiometer in the original info sheet, you can set the - terminal to anything between 0 and 5 volt. So say you set the potentiometer to its midway position: the voltage at the comparator - terminal is now 2.5 volts. That corresponds to about 10 feet.
With a truck 6' ahead of you, the sensor would output something like 1.5 volts. The comparator compares, the output is low, and the buzzer is off.
The truck ahead of you starts to pull away. The sensor output voltage starts to climb as the distance increases. 1.8v, 2v, 2.5 volts. As soon as the sensor output voltage hits 2.5 volts (10 feet), the comparator output goes high, and the buzzer sounds.
The way you drew the circuit, as soon as the truck ahead of you is more than 0 feet away, the buzzer sounds. That's pretty useless.
You need to set the - terminal of the comparator to a voltage that corresponds to the distance you want to buzzer to sound.
You could replace the potentiometer with 2 resistors. I would just keep the potentiometer in the circuit. You don't have to put it on the dash, you can set it to what you like and put it in the electronics box. You can use any potentiometer. The ohm value doesn't matter. All that matters is that the potentiometer is rated for enough watts. In this case, the potentiometer watts should be greater than 25 divided by ohm value, which is going to be basically any potentiometer bigger than a pencil eraser.
Edited by WildBuckwheat 3/20/2016 13:26
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Question on schmatic of truck movement sensor system.Pic
