Does the obstacle LED every blink when you wave your hand if front of the sensor?
Have you tried adjusting the pot when you do this?

The 74194 requires a minimum input risetime of 500ns, and the opt sensor is likely slower than that.
You need to add a Schmitt-trigger IC, such as the 7413 or 7414, at its output.

 

Hello,

Is the output changing when an object is in front of it?
If not, it could be that the transmitter and receiver see eachother to much.
You could put a piece of cardboard between the transmitter and receiver.

Bertus

 

The 74194 requires a minimum input risetime of 500ns, and the opt sensor is likely slower than that.

If the sensor IC is an LM393, that has a "response time" of ~ 1.5uS per the datasheet.

 

Using a 555 to invert the output to a positive pulse.

 

If the sensor IC is an LM393, that has a "response time" of ~ 1.5uS per the datasheet.

The concern is the rise-time, not the response time, which are unrelated.
The rise-time of an LM393 is determined mainly by the value of the output pull-up resistor and the output capacitive load.

 

The concern is the rise-time, not the response time, which are unrelated.

Is there a universally accepted definition of "response time", or do different manufacturers mean different things by it ?

 

If the sensor IC is an LM393, that has a "response time" of ~ 1.5uS per the datasheet.

That response time is propagation delay. What is important is risetime. The negative transition time will be <200ns, but the positive transition time is proportional to the pullup resistor. I would add a 1k pullup resistor on the output.