IR problems

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- 2nd August 2007, 06:13
Snap

IR problems

I would like a clean crisp voltage drop to give my pic a definite 0 or 5 volt difference. the problem is that if I am using an IR transistor (which I need to use) I can dim the led (with a comparitor circuit) by slowly covering the ir reciever (collector). My question is this.. can I create a circuit that will not dim a led ( meaning not a definat on or off) when I need a digital high or low signal... and I have already tried the 741 op amp comparitor. It dims the led as much as the straight transistor does. Could it be the resistors involved?
all I want is a way of telling the pic that I have a high (5 v)or low (<1.5v)signal. I think it is called hysteria,, Would a shmit trigger work?
Thank You For The Great Work
Snap
- 2nd August 2007, 10:19
keithdoxey

Quote:

Originally Posted by Snap

I would like a clean crisp voltage drop to give my pic a definite 0 or 5 volt difference. the problem is that if I am using an IR transistor (which I need to use) I can dim the led (with a comparitor circuit) by slowly covering the ir reciever (collector). My question is this.. can I create a circuit that will not dim a led ( meaning not a definat on or off) when I need a digital high or low signal... and I have already tried the 741 op amp comparitor. It dims the led as much as the straight transistor does. Could it be the resistors involved?
all I want is a way of telling the pic that I have a high (5 v)or low (<1.5v)signal. I think it is called hysteria,, Would a shmit trigger work?
Thank You For The Great Work
Snap

It would be helpful if you could describe the application more clearly.

What are you trying to make ?

If it is an IR receiver then using a dedicated IR Receiver module is by ar the most reliable.

If it is some form of beam break device then again I would use a dedicated IR receiver module but you would need to modulate the IR source with a 38kHz carrier.
- 2nd August 2007, 13:18
Bruce

Most PICs have a few Schmitt Trigger inputs. Some have comparators. So
you can probably make it work without any additional hardware. Just use a
pin with a Schmitt Trigger input buffer, or the built-in comparator.

In the PIC data sheet, the port block diagrams show which pins have Schmitt
Trigger input buffers.

The Electrcal Specifications section of the data sheet shows what the min
and max input levels are for high/low signals on different input types.

As Keith mentioned, the simplest way would be to just use an IR module with
a built-in band-pass filter of 38 or 40kHz, and modulate your IR LED at the
band-pass frequency of the module.

These respond pretty fast with a low-going signal when the IR LED is on, and
high-going signal when it's off. They work pretty much the same on TTL or
Schmitt Trigger inputs.

They are also less sensitive to ambient light than most IR photo transistors,
and have built-in filters to block light outside the IR wavelength.

So you save a ton of board space, use fewer parts, and save yourself a little
hysteria..;}
- 2nd August 2007, 13:34
Snap

Thank you for the help

I am making a simple beam breaker. I have an infra red emitter and detector (photo transistor) but need to get the signal into the pic (16f84a). I was just wondering how to start with the cleanest signal I could (0 or 5 volts not 1.2 or 2.3 volts) I perfer not going with the pre-made units because I am trying to understand how it works. All of the circuits I find involve op amps and technically the out put should but just that (0 or 5volts) or pretty darn close. I set it up and if I break the beam very slowly you can see the led dimly start to light before it comes fully on. I played around with lots of resistor combinations but it does not seem to make a difference. I want a relay type of instantanious change.
Thanks again for your help and sorry for the Hysteria I am a big Def Lepard fan and I can't find the spell checker on this thing.
- 2nd August 2007, 17:28
Bruce

Here's one example using a comparator. http://home.cogeco.ca/~rpaisley4/ATDetIR.html
- 2nd August 2007, 19:06
mackrackit

1 Attachment(s)

Here is one I am using for a "Laser Fence". It will also work for IR.
http://www.picbasic.co.uk/forum/atta...1&d=1186075823
And the simple code to go with it.

Code:

DEFINE OSC 4 Asm ERRORLEVEL -306 Endasm include "modedefs.bas" ANSEL=%00000000 CMCON=7 PAUSE 2000 TRAIN VAR BYTE TRAIN=$55 CNT VAR BYTE LP VAR BYTE START: COUNT PORTC.1,100,LP IF LP <> 1 THEN CHECK HIGH PORTC.5 PAUSE 50 LOW PORTC.5 PAUSE 50 GOTO START CHECK: COUNT PORTC.1,100,LP IF LP <> 1 THEN BREACH GOTO START BREACH: FOR CNT = 1 TO 5 SEROUT PORTC.4,T2400,[TRAIN,TRAIN,TRAIN,TRAIN,TRAIN,9,3] HIGH PORTC.5 PAUSE 100 NEXT GOTO START END

R2 will adjust the sensitivity of the Photo Diode. Ambient light does need to be shielded. Have used the same with IR but R2 was a fixed 10meg. (Total darkness for a parts counter on a conveyor)

Using 3 volts because of the radio transmitter.
- 2nd August 2007, 19:24
mackrackit

1 Attachment(s)

Looks like I need a lesson on image tags!
<img src="http://www.picbasic.co.uk/forum/attachment.php?attachmentid=1904&stc=1&d=118608738 4">

Got it!!
- 2nd August 2007, 20:27
Snap

I am happy there are more people out there building things for their .....ahem..childrens amusment. Mine is a slot car track for my son. Bruce small internet I used the exact same schematic you sent me for the lay out and it is the one that is giving me the problems but Im sure I am being too sticky about the details and tonight I will try it out with the pic with the fence circuit and see how it works (in sure it will be great).
Thanks again for the help I will post if it works or not.
Snap
- 2nd August 2007, 21:03
Pic_User

image tags

Quote:

Originally Posted by mackrackit

Looks like I need a lesson on image tags!

Found this:
[html]<img src="http://www.picbasic.co.uk/forum/attachment.php?attachmentid=367">[/html]By: Darrel
Here:
http://www.picbasic.co.uk/forum/show...98&postcount=2
- 2nd August 2007, 21:56
mackrackit

Quote:

Originally Posted by Pic_User

Found this:
[html]<img src="http://www.picbasic.co.uk/forum/attachment.php?attachmentid=367">[/html]By: Darrel
Here:
http://www.picbasic.co.uk/forum/show...98&postcount=2

Thank you Pic_User! Learn something every day.
- 6th August 2007, 06:20
Snap

It works ???

Ok, I got my ir detect to work on a pic 16f84a the secret is to ignore all of the internet info out there that suggest op amps comparators. The pic is smart enough to read a slightly variable input (you might have to pull up of down the port). and job is done. After all was working It still bugged me that I could not get the 741 op-amp working so I spent the night playing with diffent combinations of resistors and leds untill I thought I figured this little sucker out of course I will be wrong ...but I can tell you that the fence circut works.
Thank again for the speedy help
Snap