High speed photography

oracacle

Senior Member
#1
After seeing a Picaxe based unit on the internet I saw now reason why I could not build one of these units my self. after quite a lot of testing and waiting for parts to arrive I eventually came to a design that seems to work extremely well

the circuit:
Proto-0.3 by f2268d215cc925918731918f4efa0289, on Flickr

I ended up using the on-chip comparators to fire an interrupt. The system is able to control both the shutter of the camera and the flash via a modified sync cable. Due to the fact that this kind of photography normally happens in a dark room being able to see what you are doing was an important factor that needed to be addressed. This was done by using a torch with a broken switch and modifying it to receive power from the system, this means when "Run" is pressed it switches the torch off, opens the shutter and waits for the signal from the sensor.

The comparators make use of the IVR, this allow the user to easily make changes to the point at which the signal changes the state of the interrupt flag - essentially meaning they can change the sensitivity of the inputs.
The primary sensor at the minute is the sound detector provided rev Ed http://www.picaxe.com/docs/picaxe_sound.pdf

there where many test shots normally involving a hammer and something being smashed - I found that walnuts are very tasty. after the initial testing found the that everything was working well I moved to something a little more interesting

Water-ballon-0 by f2268d215cc925918731918f4efa0289, on Flickr

Water-balloon-1.2 by f2268d215cc925918731918f4efa0289, on Flickr
this shot had an added 1.2ms delay

I should have used a greater f-stop but I am still learning this new technique.

The final setup allow for adding a delay between the signal and the output, the ability to strobe the flash and to make use of multiple camera settings including burst, single, mirror up and bulb mode
 

oracacle

Senior Member
#3
Thanks, I will try and get some more detail up in the coming days but work is starting to get in the way with xmas already upon the retail industry
 

hippy

Technical Support
Staff member
#4
Superb photographs.

One of the problems in answering "could a PICAXE do it?" was not knowing what the reaction times would have to be. If, when you have some time, you could document what sort of delays from event to grabbing an impressive photograph are I believe that would be very useful. It appears we are talking up to a couple of milliseconds from your post.
 

oracacle

Senior Member
#5
The sound detector was about 40cm away from the balloon which gives a sound travel time of about 1.1ms. The first shot had no extra time added in. The second shot had some extra time added,I will try and correct stone data on the time between the input the flash bring fired but I only have the pcb scope to collect the info.

I will upload a copy of the code during the week so you can do some testing of your own if you do wish
 

oracacle

Senior Member
#6
I have done some screen grabs of DP scope, I will try and go into the number in a little more detail in a while
first default settings with zero point on the detector giving an ADC reading of about 40 and average sensitivity setting, IVR set to 128
Default by f2268d215cc925918731918f4efa0289, on Flickr

Next I set the zero point to around 78-80 and turn the sensitivity up to about 2 thirds and turned the IVR down to 88. This was used to catch the first shot with the balloon still receding around the water
0 pause sens by f2268d215cc925918731918f4efa0289, on Flickr

next was the same but with 1.25ms delay added, used for the second shot where the balloon seems to have completely receded
1.2 pause sens by f2268d215cc925918731918f4efa0289, on Flickr

these time were taken between the time of input and output to the system and does not take into account the time taken for the detector to processes the signal or the travel time from the source to the mic itself. It should also be noted that when the system enter the holding loop to wait for the interrupt the clock speeds are moved for 8mhz to 64mhz, and return to 8mhz after detection is complete. I cursory look at the data exported from DP scope shows that the first balloon settings with the lower IVR, higher zero point and sensitivity was the fastest with as little as 0.00015 seconds response, default showed 0.00025, the added 1.2ms (with higher sensitivity IVR and zero point) delay shows 0.0014 seconds. Please again remember that these time do not current take into account the time for the detector to process the sound signal or the amount of time it takes the sound to travel to the mic.

The IVR is interpreted in the form of ADC readings, with the 28x2 with the 4 bit IVR setting (256/32)*IVR. I did this to make the information easy for user to understand in the relation to sensor ADC readings.

Also please note that there is an error in the circuit diagram, the pull down on A.0 and A.1 were changed for 10k from the displayed 220M. this stopped the pins from floating wildly if the sensor was not connected and firing before the event had taken place. This problem was further resolved by allowing the user not only to deactivate either of the sensor but also choose which sensor will cause the interrupt.


If the speed of sound is around 340m/s, and with a known distance - in the case of the balloons 40cm or 0.4m - and the known calculation of time = distance/speed we get a number of 0.00118 seconds. if we add this to the fastest time for the first shot we get 0.00118 + 0.00015 = 0.00133 second plus the small time it take for the detector to do its thing - this as I understand it is around or less than 100us giving a final figure of 0.00143.

I am currently wondering if it would be possible to connect the mic directly to the ADC to improve that figure, I have a spare electret mic here so may look into it
 
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oracacle

Senior Member
#8
I have done some more work to this project and it has evolved into something more than just high speed photography.
It now a shutter timer that not only controls how long to wait before the shutter opens, but also how long the shutter stays open for. Its also a simple time lapse controller.
There is more in the pipeline, but between not being 100% well and work getting in the way I haven't had time to look at the ideas in the fullest way.

here are the 2 include files, limit of 2 files per upload
 

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#10
And here is the timer section, apparently still under construction, but does seem to work as intended. I suspect it just means there was some thing I was intending to remove after confirmation that it did work.
 

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