Proximity sensor - help for a school project

[ericgibbs]

hi,
The values of the voltages you posted.

+Vs - 9,6v
A - 0,48v
B - 0
C - 0
D - 0
E - 0,05v

Show that pin 7 of the 555 has no voltage on it, this is what you would expect if the IR detector was not receiving a signal from the transmitter.

Under this condition of no input to pin7, the output pin3 will always be high after power up. This is a flaw in the circuit design.

The voltage you have on pin3 [output] of the 555 is driving the buzzer.

If you measured D3 while its soldered to the pcb, the resistance measurement is not reliable.
The only function of D3 is to slightly forward bias D4, so that low level signals can be rectified.

As I explained the circuit works OK on a simulator, with the exception of the power up latching the 555 pin3 output high.

This can be cleared by placing the emitter diode close to the receiver diode so that D4 can drive the inputs of the 3 comparators.

Do you follow.?

 

[DWBH]

Humm... got it!

It bips now, although only when both leds are facing each other. It doesn't detect objects very well, the led's range must be too narrow, because there must be some angle between the leds, so that they aren't parallel to each other.

 

[ericgibbs]

Humm... got it!

It bips now, although only when both leds are facing each other. It doesn't detect objects very well, the led's range must be too narrow, because there must be some angle between the leds, so that they aren't parallel to each other.

hi,
Looking at the idea of reflecting IR from an 'non cooperative target' [ a surface not designed as a reflector] is very hit and miss.

If the IR emitter and detector are not aligned correctly and the reflecting surface is not perfectly flat, the design is a very poor way of detecting distance.

The point also to note if you run at 9V and not 12V the power output of the emitter is reduced.

Whats the plan now for the project.?