Good day,
I'm working on a IR camera trigger that will fire a camera when an IR beam is broken. Initially I just had an IR LED on the transmitting side, and an IR phototransistor on the receiving side (with a transistor and variable resistor for sensitivity adjustment). This worked indoors, but was almost useless outside because the high and changing ambient light made it impossible to find an effective sensitivity level.
Following some suggestions from the forum, I'm now working on a version that uses a 555-powered 38 khz modulated IR and a receiver/decoder from a VCR. After building the circuit I discovered to my dismay that the receivers I have (and apparently most other 38 khz receivers also) can't handle an uninterrupted signal from the transmitter. The active-low output from the receiver will only stay down for a fraction of a second when a steady signal hits the receiver before bouncing back up to the no-signal level. Based on some tests with a scope and a MCU-generated signal, it seems that there has to be a gap of a millisecond or so between pulses, and the pulses themselves can't be very long.
I could put a MCU on the transmitter and pulse the output, but then I'd have to have a filter of some kind at the receiving end. This would also add a delay to the response, which isn't so good for fast moving subjects (hummingbirds and the like).
According to a post on the parallax forum (http://forums.parallax.com/showthread.php?t=103026) Waitrony makes an IR receiver that can handle a continuous 38khz signal -- the PIC-2T26ASMB. Unfortunately, I haven't been able to find anywhere to buy one of them!
If all else fails, I might try putting a uC on the receiving end with two receivers and switching them on and off alternately every few ms. This is an awkward solution though (and probably a troubleshooting nightmare for my skill level!), which I'd like to avoid if at all possible.
So my questions are:
1) does anyone have a suggestion for where I could get one of the Waitrony receivers, or does anyone know of an alternate part?
2) can anyone think of a good way of using an intermittent signal effectively, or maybe using some other type of modulation altogether?
3) why do the IR receivers "overload" and stop recognizing the incoming signal (something in the AGC?), and is there maybe a way to trick them into behaving better using external components?
Thanks very much for your help! There's a pack of wolves frequenting our property these days, and my brother (who I gave the original trigger to) is a keen nature photographer -- so I'm hoping we can catch a shot of them going about their business from a safe distance!
Thanks,
Adam
I'm working on a IR camera trigger that will fire a camera when an IR beam is broken. Initially I just had an IR LED on the transmitting side, and an IR phototransistor on the receiving side (with a transistor and variable resistor for sensitivity adjustment). This worked indoors, but was almost useless outside because the high and changing ambient light made it impossible to find an effective sensitivity level.
Following some suggestions from the forum, I'm now working on a version that uses a 555-powered 38 khz modulated IR and a receiver/decoder from a VCR. After building the circuit I discovered to my dismay that the receivers I have (and apparently most other 38 khz receivers also) can't handle an uninterrupted signal from the transmitter. The active-low output from the receiver will only stay down for a fraction of a second when a steady signal hits the receiver before bouncing back up to the no-signal level. Based on some tests with a scope and a MCU-generated signal, it seems that there has to be a gap of a millisecond or so between pulses, and the pulses themselves can't be very long.
I could put a MCU on the transmitter and pulse the output, but then I'd have to have a filter of some kind at the receiving end. This would also add a delay to the response, which isn't so good for fast moving subjects (hummingbirds and the like).
According to a post on the parallax forum (http://forums.parallax.com/showthread.php?t=103026) Waitrony makes an IR receiver that can handle a continuous 38khz signal -- the PIC-2T26ASMB. Unfortunately, I haven't been able to find anywhere to buy one of them!
If all else fails, I might try putting a uC on the receiving end with two receivers and switching them on and off alternately every few ms. This is an awkward solution though (and probably a troubleshooting nightmare for my skill level!), which I'd like to avoid if at all possible.
So my questions are:
1) does anyone have a suggestion for where I could get one of the Waitrony receivers, or does anyone know of an alternate part?
2) can anyone think of a good way of using an intermittent signal effectively, or maybe using some other type of modulation altogether?
3) why do the IR receivers "overload" and stop recognizing the incoming signal (something in the AGC?), and is there maybe a way to trick them into behaving better using external components?
Thanks very much for your help! There's a pack of wolves frequenting our property these days, and my brother (who I gave the original trigger to) is a keen nature photographer -- so I'm hoping we can catch a shot of them going about their business from a safe distance!
Thanks,
Adam