light beam switch needed

Original Burnedfingers · 23rd April 2012, 02:57 PM

Hi,

I need a circuit to allow a relay to be activated and power a small geared down motor when a photo transistor sees the light from a IR LED and to deactivate the relay when the beam isn't seen. I am passing an object of roughly .450 in diameter inside a 1/2 ID pipe. When the pipe is full I need the motor to stop.

Any ideas?

KatieandDad · 03:13 PM

The problem with such a design is ambient light and false triggering.

Simplest way to ensure no false triggering is to use an NE555 (for example) to generate a known frequency and then just use its PLL counterpart (I can't remember it off the top of my head by I seem to recall the NE564) to detect it.

http://noel.feld.cvut.cz/hw/philips/acrobat/1057.pdf

Original Burnedfingers · 23rd April 2012, 03:14 PM

It would be a black tube so light shouldn't be a problem.

KatieandDad · 23rd April 2012, 04:11 PM

In which case its pretty simple.

You simply need to wire up the IR LED exactly as you would any other LED with a series resistor.

The sensor is an IR transistor (assuming its NPN) with its Base OPEN CIRCUIT (Normally - they do differ), Emitter to 0V and its Collector to the -ve of the motor. The +ve of the motor is connected to VCc.

Might be better to switch the motor with a relay to reduce the current through the IR transistor.

Original Burnedfingers · 23rd April 2012, 06:54 PM

will this work?

gmphadte · 24th April 2012, 06:17 AM

Use 555 as schmitt trigger.

Gajanan Phadte

Original Burnedfingers · 24th April 2012, 11:25 AM

I don't want a schmitt trigger.

23rd April 2012, 02:57 PM	#1
Original Burnedfingers diyAudio Member Join Date: Nov 2002	light beam switch needed Hi, I need a circuit to allow a relay to be activated and power a small geared down motor when a photo transistor sees the light from a IR LED and to deactivate the relay when the beam isn't seen. I am passing an object of roughly .450 in diameter inside a 1/2 ID pipe. When the pipe is full I need the motor to stop. Any ideas?

23rd April 2012, 03:10 PM	#2
KatieandDad diyAudio Member Join Date: Nov 2011 Location: UK	The problem with such a design is ambient light and false triggering. Simplest way to ensure no false triggering is to use an NE555 (for example) to generate a known frequency and then just use its PLL counterpart (I can't remember it off the top of my head by I seem to recall the NE564) to detect it. http://noel.feld.cvut.cz/hw/philips/acrobat/1057.pdf Last edited by KatieandDad; 23rd April 2012 at 03:13 PM.

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23rd April 2012, 03:14 PM	#3
Original Burnedfingers diyAudio Member Join Date: Nov 2002	It would be a black tube so light shouldn't be a problem.

23rd April 2012, 04:11 PM	#4
KatieandDad diyAudio Member Join Date: Nov 2011 Location: UK	In which case its pretty simple. You simply need to wire up the IR LED exactly as you would any other LED with a series resistor. The sensor is an IR transistor (assuming its NPN) with its Base OPEN CIRCUIT (Normally - they do differ), Emitter to 0V and its Collector to the -ve of the motor. The +ve of the motor is connected to VCc. Might be better to switch the motor with a relay to reduce the current through the IR transistor.

24th April 2012, 06:17 AM	#6
gmphadte diyAudio Member Join Date: Jul 2003 Location: Dona paula, Goa	Use 555 as schmitt trigger. Gajanan Phadte

24th April 2012, 11:25 AM	#7
Original Burnedfingers diyAudio Member Join Date: Nov 2002	I don't want a schmitt trigger.