Continue to Site

Welcome to our site!

Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

  • Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

Replacing an NPN for a PNP in the following circuit?

Status
Not open for further replies.
The most reliable way of making a beam-break detector that eliminates most of these issues is to pulse the emitter at a super-audio rate, and then use an AC-coupled amplifier/envelope-detector following the IR detector. There are lots of posts to these forums about using the commonly-available 38kHz IR TV remote control receivers. They are ac-coupled, have lots of gain only at the emitter chopping frequency, have a lot of immunity to sunlight and artificial lighting.
 
sounds interesting, I will have to do some research as you are talking well above my (current) knowledge point, but I'm willing to learn! The only reason I was told to keep it as simple as possible was (and this may be complete bunkem, but again, past my knowledge base) that the more components, the more time lag introduced, and essentially the sensor has to be able to react and create an output from an object about 10mm long travelling at about 500m/s...
 
sounds interesting, I will have to do some research as you are talking well above my (current) knowledge point, but I'm willing to learn! The only reason I was told to keep it as simple as possible was (and this may be complete bunkem, but again, past my knowledge base) that the more components, the more time lag introduced, and essentially the sensor has to be able to react and create an output from an object about 10mm long travelling at about 500m/s...

You have some difficult to meet requirements. It would have been nice if you had stated those up front since your last sentence above obviates the entire discussion so far!
 
my apologies, I didn't think to mention them as I knew that the circuit I posted for conversion has been used to capture events far quicker, so assumed that replacing an NPN with a PNP would not alter the speed - my lack of knowledge once again coming to the fore!
 
indeed one use of it would be very much like a chronograph! Unfortunately the nature of the ambient lighting will be variable - sometimes constant, others not.
 
indeed one use of it would be very much like a chronograph! Unfortunately the nature of the ambient lighting will be variable - sometimes constant, others not.
I have an idea, but it depends on how rapidly the ambient lighting will change. Do you know?
 
It is unlikely to be that rapid and to be honest it's not that important if I get the odd misfire through it, as long as it fires when it's supposed to!
 
Why don't you try a detector like BPW24R, which has a very narrow angle of acceptance. If you shield it with a short tube with the inside painted flat black, the effects of ambient light should be minimized. I have another idea, but this might solve your problem.
 
thanks Roff, I did have a look at a few more detectors and emitters, and am indeed going to be changing mine, though the initial problem was just trying to get the circuit working at all. My Dad took up the challenge and has managed to get a circuit working after much, much faffing, that would appear to be up to the speed requirement, just got to do some testing now!
 
Status
Not open for further replies.

Latest threads

New Articles From Microcontroller Tips

Back
Top