Hello everybody,
This is my first thread in this awesome forum.
I have an NPN photosensor with 24v supply and (of course) the two states of the output signal are 0v or open circuit.
On the other hand there is a 555 timer IC (5v load)
My question is : How can I use the output of the sensor to switch the 555 on and off.
I've thought about pnp transistor circuit like the one in this page :
http://www.mayothi.com/transistors.html
but I couldn't make it for my special case.

Thanks in advance
Waleed

 

This thumbnail describes what we think you said, but do not think it's what you want?? Throw your darts.

 

Lost thumbnail

 

Thank you Bernard
but my circuit is this

so just consider it as a resistor because my problem is how to switch it's 5v supply on and off. I mean I want the 5v on the terminal VP to be turned on and off according to the output of the sensor.
Please give me details about the kind of transistor in the thumbnail and how can I switch this transistor on and off using the output signal from the npn sensor.

Thanks again
Waleed

 

Thank you Bernard
but my circuit is this

so just consider it as a resistor because my problem is how to switch it's 5v supply on and off. I mean I want the 5v on the terminal VP to be turned on and off according to the output of the sensor.
Please give me details about the kind of transistor in the thumbnail and how can I switch this transistor on and off using the output signal from the npn sensor.

Thanks again
Waleed

So where is your NPN sensor? This is an oscillator.

 

Now it's clear I think
and the question is what is the switch that I should put to do the job?

 

I'm assuming that the photo sensor is more complex than a opto-coupler. If the out of the photo sensor is open and 0V, then maybe a PNP transistor could switch the power to the 555 circuit on and off. 0V turns on the 555, and open turns it off.

You didn't say if you wanted open to activate to 555 or 0V. I added a second circuit to give you the opposite.

Ken

 

OK, one other question, do you know a 555 drops around 1.2 V on the output? If you power it with 5V it will output 3.8V. If you power it with 6.2 it will output 5V.

Other than that it is pretty simple. Use the sensor to drive a voltage regulator that feeds the 555.

I'll sketch an idea up and post it on this post.

**********************************

There is nothing fancy about this design. There are a lot of other ideas that would work as well or better. Just adjust the output to the required voltage using R1.

 

Thanks everybody I will try and see what works best for me. I appreciate your help.