IR Amplifier

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quickrik

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Hi all,

I'm trying to build a PIC project to detect an IR signal. Any IR signal modulated at any frequency. It needs to work at about TV remote distances say 10+metres.

I'm looking for a circuit that can amplify the signal from an IR diode/transistor enough to switch the PIC input. I've seen a curcuit using an SL486 which seems ideal but this part is now obsolite and I can't find a replacement.

Thank in advance

Rik
 
Use an existing IR remote IC, almost all use a similar modulation frequency, and they aren't very fussy about it being a little wrong. These also demodulate the signal, so you don't have problems with the modulation being fed to the PIC - just a nice logic signal.
 
Sorry I really wasn't very clear in my question. The IR signal might not even be modulated, I'm just looking for any IR signal. I'm guessing this would flumex most of the TSOP type recievers or are they really not that sensitive.
Sorry I've never used them, infact i'm very novice at all electronics.
 
You really need to give more details - for receiving IR remote control signals the IC's are VERY sensitive.
 
The current curcuit I have detects the presence of IR light using an IR transistor, but it stops detecting once the source (in this example a tv remote,because thats what I had to hand, but it could be anything) if more than 10cm away. The same remote can change my TV channel from 10metres away, so theres enough power in the source to go 10metres. So simply put how can I detect IR light at ranges of 10metres. I don't need to send any data just whether the source is on or not.
 
The very sensitive IR receiver ICs for TVs and DVD players reduce their sensitivity if the IR is continuous and is not data. The data must be in bursts of 10 to 70 cycles and have a gap time of at least 14 cycles between bursts.
That is so they have reduced sensitivity to 40kHz continuous interference from sompact fluorescent light bulbs.
 
There are too many IR sources in the typical operating environment. The receiver requires a "message" to distinguish "your" source from all the others.
 
Don't use a DC connection to the IR transistor, use a capacitor, that will filter out DC (ambient light) and pass the modulated IR of the remote. That's really crude though.
 
Sceadwian said:
Don't use a DC connection to the IR transistor, use a capacitor, that will filter out DC (ambient light) and pass the modulated IR of the remote. That's really crude though.
Click to expand...

Great so that will filter out other sources of IR. Would. that capacitor go in series what size should it be.

This still won't help me with my range issue will it?
 
quickrik said:
Great so that will filter out other sources of IR. Would. that capacitor go in series what size should it be.

This still won't help me with my range issue will it?
Click to expand...

We don't know, you've still never told us EXACTLY what you're trying to do.
 
Motorbike/car goes around a circuit. PIC logs various thing its doing speed,revs etc. Every lap I need to detect a new lap has started, in order to compare laps. Most circuits enable this by means of an IR beam across the start/finishline. Different circuits use different modulated beams, some encode the beam (send data) some not, some circuits don't have a beam at all and you supply your own beam.

So I need something that can detect any IR beam at up to the width of the track 10metresish, does that help?
 

Yes, but if you try and make something to accept any random type of signal, it won't be much good at any of them.

As suggested, it's pretty well essential that the IR is modulated in some way, and that the receiver (if you're building your own) is AC coupled - otherwise bright sunlight will swamp it anyway.
 
Well I'm up against here. I know it can be done. I just need a little help with the how. I borrowed a friends commercial receiver and I can make it trigger with my zero lux video camera which is just active un-modulated IR. I'd like to pull it open but its a sealed unit and not mine.

I 'm back to square one with a circuit that works for me but I need to extend its range. And from what Im being told then I have to deal with the ramifications of making it more sensitive. Wow is electronics this tricky? It worse than computers
 
Electronics isn't tricky. Your application is tricky.

1) You have tried a circuit that has low gain. You didn't post its schematic and parts list so we can't improve it.
2) We discussed the TSOP TV remote receiver. It reduces its gain for some of your signals.
 
Heres my circuit.

D1 is just an LED which I use in the code to display what the IR diode sees (RC3=RC1)
D2 is a phototransistor (my software only has a photodiode symbol) salvaged from a mouse wheel
U2 = 7805

Also connections for a alphanumeric LCD for debugging.

As you can see there is nothing done to the IR signal hence the low gain.

Many thanks for the help

Rik
 

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Not only there is not an amplifier but the photo-transistor is an emitter-follower that doesn't have any gain.

If the photo-transistor has its emitter grounded and a collector resistor (try 100k) then it would have a gain of about 100.
 
I have to confess when I first read this it went right over my head, but in the true spirit of RTFM. I did some reading and then thought I understood, so I rewired the IRtransistor as such 5v to 2x50k resistors to IRtransistor to ground. Then taking the PIC feed between resistor and IRtransistor.
Alas - nothing, couldn't get the PIC to go high when incontact with IR.

Have I understood you correctly? or have i wired some up wrong?
 
You don't know what you are doing.
You forgot to attach a schematic so I don't know what you are doing.

Connect the photo-transistor like this. The output to the PIC is high without IR and goes low when IR or light is received.
 

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True. If I knew what I was doing I wouldn't need to ask questions here.

I have interpreted your comments correctly and its wired correctly as i described it. I now fear my salvaged part is not all it should be I shall pruchase a new photo transistor and try later.

thanks for the help.
 
If you know the part number of the photo-transistor then look up its datasheet to see which pin is which.
 
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