Hello folks,
I'm building a simple automatic camera trigger using an infrared LED and photodiode to trigger the camera when an object moves into the target area. I have built a version of the device and it works well under test conditions, but becomes unreliable and finnicky when I actually try to put it to use.
Here is a schematic for the receiver in its current configuration:
R1 is used to adjust the sensitivity. The camera requires only a very small amount of current to trigger the shutter -- a 1 meg resistor across the camera terminals will trigger it. The basic design here came from a very brief article about typical photodiode circuits.
The problem I'm having is that under real-world conditions (especially outdoors), I can't seem to get the sensitivity adjusted so that the trigger will fire only when the beam is broken. It likes to either fire randomly, or continuously, or not at all. With plenty of adjustment I can occasionally get it to trigger properly, but after being left for a while it goes out of whack with slight changes in ambient light level (or sometimes even when there shouldn't be any ambient light level changes, such as at night).
Initially I used only one IR LED. I added two more LEDs, figuring that the signal level just wasn't strong enough, but it seemed to make very little difference -- one reason I suspect that my circuit needs some improvement.
I have also had a piece of tubing around the photodiode to shade it from ambient light, but again without satisfaction.
Essentially my question is what is the best way of using a continuously changing resistance (in this case the IR photodiode) to control an on/off switch. (An additional drawback of the design I've used here is that when ambient light levels are high, there is has to be a continuous current going through the resistor and photodiode, which seems like an unnecessary drain on the battery.)
My knowledge of electronics is quite limited -- if my description or schematic contains errors or instances of newby nonsense, or there is critical information lacking, please let me know
Thanks in advance for your help,
Adam
P.S.
Probably the ideal set up would use a modulated IR light, which the receiver would recognize while ignoring the ambient, unmodulated IR. There is a product that uses this principle from Qkits ( http://store.qkits.com/moreinfo.cfm/QK130 ), but the trigger delay makes it unsuitable for photography. I have a 555 timer that I think I could use for generating the signal, but I'm not sure how I would be able to interpret it on the receiving end. If anyone knows of a system like that which I could buy, or where I could find out how to make one, that would be great.
I'm building a simple automatic camera trigger using an infrared LED and photodiode to trigger the camera when an object moves into the target area. I have built a version of the device and it works well under test conditions, but becomes unreliable and finnicky when I actually try to put it to use.
Here is a schematic for the receiver in its current configuration:
R1 is used to adjust the sensitivity. The camera requires only a very small amount of current to trigger the shutter -- a 1 meg resistor across the camera terminals will trigger it. The basic design here came from a very brief article about typical photodiode circuits.
The problem I'm having is that under real-world conditions (especially outdoors), I can't seem to get the sensitivity adjusted so that the trigger will fire only when the beam is broken. It likes to either fire randomly, or continuously, or not at all. With plenty of adjustment I can occasionally get it to trigger properly, but after being left for a while it goes out of whack with slight changes in ambient light level (or sometimes even when there shouldn't be any ambient light level changes, such as at night).
Initially I used only one IR LED. I added two more LEDs, figuring that the signal level just wasn't strong enough, but it seemed to make very little difference -- one reason I suspect that my circuit needs some improvement.
I have also had a piece of tubing around the photodiode to shade it from ambient light, but again without satisfaction.
Essentially my question is what is the best way of using a continuously changing resistance (in this case the IR photodiode) to control an on/off switch. (An additional drawback of the design I've used here is that when ambient light levels are high, there is has to be a continuous current going through the resistor and photodiode, which seems like an unnecessary drain on the battery.)
My knowledge of electronics is quite limited -- if my description or schematic contains errors or instances of newby nonsense, or there is critical information lacking, please let me know
Thanks in advance for your help,
Adam
P.S.
Probably the ideal set up would use a modulated IR light, which the receiver would recognize while ignoring the ambient, unmodulated IR. There is a product that uses this principle from Qkits ( http://store.qkits.com/moreinfo.cfm/QK130 ), but the trigger delay makes it unsuitable for photography. I have a 555 timer that I think I could use for generating the signal, but I'm not sure how I would be able to interpret it on the receiving end. If anyone knows of a system like that which I could buy, or where I could find out how to make one, that would be great.
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