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Step 20Sensor Applications
Sound
UPDATE: EDITED
A microphone is one of the most versatile sensor inputs in your arsenal.
The obvious idea of balloons popping and things breaking is, however, a little more complex. Because a balloon bursts so quickly, camera lags are often too long to actually take the picture. A prefocused D90 takes 0.07 seconds to shoot, wheras a balloon could be fully burst in under a millsecond (I am told by reliable sources). How to get round this?
a) Shoot it with something! If you shoot the balloon with something travelling under the speed of sound, you can trigger instantly or one/two milliseconds after you get the trigger condition met. Again you run up against the balloon popping a bit quickly...!
b) Rig up a flash and resort to bulb mode - i hate to do this because it adds complications like requiring a pitch black room to prevent overexposure - but if you add another wire out and some code to send a signal down it when you want to take a picture, you can fire the flash faster than your camera can open its shutter. This is, i'm afraid, one of the only ways you can take these pictures until you can buy a camera with shutter lag under half a millisecond. But, the controller is still capable - remember - you've got all the source code and schematics, modify and try it!
First note down the ambient value. Then, clap your hands and see how the value changes. You can use the LEDs to assist you with this.
Set the ADC trigger value to be around your hand clapping value or slightly above (use the potentiometer to set the gain).
The delay is where you can be creative and you might need a little mechanics. If you set a short delay, or even zero, you will take a picture the instant the noise peaks.
Some other applications that you might not have thought of include sports. If you're taking a picture at a cricket/baseball match with a long lens, you can set the audio trigger up to fire precisely when the batter hits the ball. Set a delay of 10ms afterwards and you'll see the batter post-swing with the ball (hopefully) flying towards the edge of the picture.
The usual list of high speed photography subjects that can use a sound trigger are:
1. The classic, water balloon filled with water (tricky)
2. Things breaking (see balloons)
3. Guns firing or things being shot at
4. Popcorn (put it on a hot pan and wait for the pop!)
5. Anything else that makes a sound :)
Light
NOTE: The pictures below were all taken using the controller and the circuit i mentioned in an earlier step. Delays were set from around 20ms to 150ms. I didn't have a proper rig so apologies for not knowing exact timings - it'll vary on your setup anyway. Note to self, by a pipette or dropping bottle!
Light is where we can be a bit more inventive.
One idea is to shine a laser pointer at an LDR. What you've just made is a simple tripwire. You could use it to take a picture when someone enters a room, when your dog eats its dinner. You could even put it outside and take a picture when a bird sits on your bird table (though this is better done with an infrared or ultrasound motion sensor).
Another application for the above is quite nifty. Ever wonder how people get those lovely pictures of water droplets hitting the surface of a pool? Well, if you set up your laser and your LDR so that the beam shines through the path of some droplets, it's a simple matter of aiming your camera at the surface of the water, focus it manually and then set the trigger to fire when the beam is broken. When the water falls through, the light will diffract and scatter and your camera fires. You then calculate how long it'll take the beam to fall and you set the delay accordingly.
Next is lightning. Now, with a fast LDR or even better, a photodiode (though these cost a bit more), you can take pictures of lightning strikes. When the lightning flashes, you have a small window in which to take your picture. Prefocus the camera on infinity and point it at the horizon, you don't want it trying to focus when you take the picture. Lightning strikes in a specific way, there is first a stepped leader, from the cloud to the ground. Then, the main visible part of the lightning, an upward stroke along the same path. After that there are normally a couple of extra discharges and the whole process takes around a tenth of a second.
The D90 that i have has a shutter lag of around 63ms pre-focussed. What this means is that if you stop your aperture down to say f/10 and take a 1 second exposure when the trigger sees lightning, you should get the shot. Provided the shutter lag is under 100ms, you'll hopefully get it. Don't bother about putting delay, the shutter will be open for plenty of time.
One thing i almost forgot about was fireworks. No longer do you have to guess when to take the shot or pray on bulb that everything will work! Simply point your LDR to the sky, wait for the flash, set a reasonably long delay - most fireworks will linger for a second or so, perhaps 100ms to allow the explosion to fully expand - and then take a second or two's exposure. Hey presto - instant gratification =D With Guy Fawkes' night approaching fairly soon in the UK, i'll be sure to try this one out. You could trigger this with sound, but it's unlikely to be as good unless you're very close to the explosion due to sound being pretty slow.
Ultrasound
Ultrasound sensors can be used to create distance or proximity modules based on the time it takes for an ultrasound pulse to return from a reciever to a transmitter. This generally needs to be done in software, so would either need a separate controller - perhaps an ATTiny45 or an ultrasound module like this one: http://www.rapidonline.com/Electronic-Components/Sensors/Ultrasonic-Sensors/Ultrasonic-range-finder-SRF05/82276. Going the DIY route is by far cheaper!
The Tiny45 does have a PWM controller to produce an "analogue" voltage signal which you could use, or it could just send out a single pulse.
This could be used as a much more effective way of taking pictures of things going past than a light sensor. Applications include macro wildlife photography (say of birds when they sit on the bird table) or security.
Odd sensors, temperature and float
You could do some odd things like take pictures when things overheat, when things overflow - hey, it's your imagination not mine!
I've seen some awesome pictures online of some other light triggered pictures including a lighter being flicked on. You could expand this theme with a match being struck in the dark.
More choices! And the LDR is cheap and easy to implement as well =D
Logic Levels
The most versatile option is adding a connection from an external circuit. Sending a logic level one or zero will work as a trigger input. This gives you infinite flexibility. You can add a really complicated circuit that will provide a "shoot" logic level based on a combination of lots of sensors rigged up to each other. The possibilities are endless!
A side note on water droplets:
This video is an excellent example of the formation of a perfect droplet. You can see the stages in my uploaded photos too. First the drop impacts, creating the "crown". This quickly decays into a more globular structure forming a concave indent on the surface. A secondary drop is then projected upwards (in a kind of 3D parabola - sombrero type shape) if the initial impact was large enough. This is in the fourth picture below. Finally this subsides and you're left with a slightly disturbed surface.
It's a good way of picking the shots you want. Clearly, the ideal moment to take a picture is about 10-20ms after the droplet hits the water. The crown decays rapidly so there's only a small window to take the picture. If you don't want to involve trial and error with this, you MUST drop the water from the same height every time with similar sized droplets - otherwise altering the decay has little effect.
http://www.youtube.com/watch?v=RU376Bo__60
UPDATE: EDITED
A microphone is one of the most versatile sensor inputs in your arsenal.
The obvious idea of balloons popping and things breaking is, however, a little more complex. Because a balloon bursts so quickly, camera lags are often too long to actually take the picture. A prefocused D90 takes 0.07 seconds to shoot, wheras a balloon could be fully burst in under a millsecond (I am told by reliable sources). How to get round this?
a) Shoot it with something! If you shoot the balloon with something travelling under the speed of sound, you can trigger instantly or one/two milliseconds after you get the trigger condition met. Again you run up against the balloon popping a bit quickly...!
b) Rig up a flash and resort to bulb mode - i hate to do this because it adds complications like requiring a pitch black room to prevent overexposure - but if you add another wire out and some code to send a signal down it when you want to take a picture, you can fire the flash faster than your camera can open its shutter. This is, i'm afraid, one of the only ways you can take these pictures until you can buy a camera with shutter lag under half a millisecond. But, the controller is still capable - remember - you've got all the source code and schematics, modify and try it!
First note down the ambient value. Then, clap your hands and see how the value changes. You can use the LEDs to assist you with this.
Set the ADC trigger value to be around your hand clapping value or slightly above (use the potentiometer to set the gain).
The delay is where you can be creative and you might need a little mechanics. If you set a short delay, or even zero, you will take a picture the instant the noise peaks.
Some other applications that you might not have thought of include sports. If you're taking a picture at a cricket/baseball match with a long lens, you can set the audio trigger up to fire precisely when the batter hits the ball. Set a delay of 10ms afterwards and you'll see the batter post-swing with the ball (hopefully) flying towards the edge of the picture.
The usual list of high speed photography subjects that can use a sound trigger are:
1. The classic, water balloon filled with water (tricky)
2. Things breaking (see balloons)
3. Guns firing or things being shot at
4. Popcorn (put it on a hot pan and wait for the pop!)
5. Anything else that makes a sound :)
Light
NOTE: The pictures below were all taken using the controller and the circuit i mentioned in an earlier step. Delays were set from around 20ms to 150ms. I didn't have a proper rig so apologies for not knowing exact timings - it'll vary on your setup anyway. Note to self, by a pipette or dropping bottle!
Light is where we can be a bit more inventive.
One idea is to shine a laser pointer at an LDR. What you've just made is a simple tripwire. You could use it to take a picture when someone enters a room, when your dog eats its dinner. You could even put it outside and take a picture when a bird sits on your bird table (though this is better done with an infrared or ultrasound motion sensor).
Another application for the above is quite nifty. Ever wonder how people get those lovely pictures of water droplets hitting the surface of a pool? Well, if you set up your laser and your LDR so that the beam shines through the path of some droplets, it's a simple matter of aiming your camera at the surface of the water, focus it manually and then set the trigger to fire when the beam is broken. When the water falls through, the light will diffract and scatter and your camera fires. You then calculate how long it'll take the beam to fall and you set the delay accordingly.
Next is lightning. Now, with a fast LDR or even better, a photodiode (though these cost a bit more), you can take pictures of lightning strikes. When the lightning flashes, you have a small window in which to take your picture. Prefocus the camera on infinity and point it at the horizon, you don't want it trying to focus when you take the picture. Lightning strikes in a specific way, there is first a stepped leader, from the cloud to the ground. Then, the main visible part of the lightning, an upward stroke along the same path. After that there are normally a couple of extra discharges and the whole process takes around a tenth of a second.
The D90 that i have has a shutter lag of around 63ms pre-focussed. What this means is that if you stop your aperture down to say f/10 and take a 1 second exposure when the trigger sees lightning, you should get the shot. Provided the shutter lag is under 100ms, you'll hopefully get it. Don't bother about putting delay, the shutter will be open for plenty of time.
One thing i almost forgot about was fireworks. No longer do you have to guess when to take the shot or pray on bulb that everything will work! Simply point your LDR to the sky, wait for the flash, set a reasonably long delay - most fireworks will linger for a second or so, perhaps 100ms to allow the explosion to fully expand - and then take a second or two's exposure. Hey presto - instant gratification =D With Guy Fawkes' night approaching fairly soon in the UK, i'll be sure to try this one out. You could trigger this with sound, but it's unlikely to be as good unless you're very close to the explosion due to sound being pretty slow.
Ultrasound
Ultrasound sensors can be used to create distance or proximity modules based on the time it takes for an ultrasound pulse to return from a reciever to a transmitter. This generally needs to be done in software, so would either need a separate controller - perhaps an ATTiny45 or an ultrasound module like this one: http://www.rapidonline.com/Electronic-Components/Sensors/Ultrasonic-Sensors/Ultrasonic-range-finder-SRF05/82276. Going the DIY route is by far cheaper!
The Tiny45 does have a PWM controller to produce an "analogue" voltage signal which you could use, or it could just send out a single pulse.
This could be used as a much more effective way of taking pictures of things going past than a light sensor. Applications include macro wildlife photography (say of birds when they sit on the bird table) or security.
Odd sensors, temperature and float
You could do some odd things like take pictures when things overheat, when things overflow - hey, it's your imagination not mine!
I've seen some awesome pictures online of some other light triggered pictures including a lighter being flicked on. You could expand this theme with a match being struck in the dark.
More choices! And the LDR is cheap and easy to implement as well =D
Logic Levels
The most versatile option is adding a connection from an external circuit. Sending a logic level one or zero will work as a trigger input. This gives you infinite flexibility. You can add a really complicated circuit that will provide a "shoot" logic level based on a combination of lots of sensors rigged up to each other. The possibilities are endless!
A side note on water droplets:
This video is an excellent example of the formation of a perfect droplet. You can see the stages in my uploaded photos too. First the drop impacts, creating the "crown". This quickly decays into a more globular structure forming a concave indent on the surface. A secondary drop is then projected upwards (in a kind of 3D parabola - sombrero type shape) if the initial impact was large enough. This is in the fourth picture below. Finally this subsides and you're left with a slightly disturbed surface.
It's a good way of picking the shots you want. Clearly, the ideal moment to take a picture is about 10-20ms after the droplet hits the water. The crown decays rapidly so there's only a small window to take the picture. If you don't want to involve trial and error with this, you MUST drop the water from the same height every time with similar sized droplets - otherwise altering the decay has little effect.
http://www.youtube.com/watch?v=RU376Bo__60
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