Sound trigger for high speed flash photography, part 9

Some experiments with water filled balloons (about 100mL of water).  My niece was popping the balloons for me this time.  The SB-25 flash gun was set at 1/32 power.  The camera was set to f/10, ISO 200.

I am out of balloons now.  The dollar store is just down the street, but before I take any more balloon shots, I need to think about a different backdrop.

Balloon placed slightly on the side.  Notice the crown of water formed at the bottom.

Sound trigger for high speed flash photography, part 8

Another balloon pop.  I had the idea of popping it from the top.  The result looks like a cup.  For this capture, the balloon is positioned about 50cm from the microphone.  Flash output was set to 1/64.

Turqoise balloon pop.  Flash power set at 1/64.

Here is a shot of a yellow balloon popped from the bottom.  I was hoping to see something more interesting, like the shape of a parachute.  It still looks interesting with the ripples close to the edges.

Yellow balloon pop.  Flash output set at 1/64.

I had by mistake left the output power of the flash set at 100% on an earlier shot with a white balloon.  Flash output set at 100% lasts much longer than flash set to 1/64, but I don't understand the result.  Because the flash light lasts longer, one can see a ghostly shape of another balloon, but it does not explain why the balloon looks like it has not been popped.  My first attempt with a white balloon a few days ago also resulted in a shot of a full balloon.  I wonder if the white balloons collapse much slower than the colored balloons.  Strange.

White balloon pop.  Flash output set at 100%.

Sound trigger for high speed flash photography, part 7

I finally decided to draw the circuit I used for the sound trigger with the QUCS software.  Not all components are available in QUCS so I had to draw a couple of items in the schematic diagram.  These items have no electrical properties so simulation in QUCS does not work as is.

Note that the LM324 OpAmp is connected up with five pins instead of three as shown.  Pin 3 = positive input (reference signal), pin 2 = negative feedback, pin 1 = output, pin 4 = 5V input, pin 11 = ground.

Sound trigger circuit.  The capacitor polarity can be reversed?

Note also that the capacitor is a polarized capacitor, and the potentiometer is there to adjust the sensitivity of the circuit to sound.

Sound trigger for high speed flash photography, part 6

So, my hypothesis that sound traveled too slow was probably correct.  I decided to waste two more balloons tonight.  My first attempt was with a white balloon.

Notice in the first photo that the electret microphone was just about 20-25cm away from the balloon.  Here, when I popped the balloon, the flash gun fired off so quick that the shape of the balloon remained as a balloon.  I did make a mistake of puncturing the balloon from the backside.  It is possible that the rupture has opened a wide gaping hole that cannot be seen from this angle.

On my second attempt with a green balloon, it was more impressive.  It can clearly be seen that half of the balloon went missing.  This time around, I held the balloon a little further away from the microphone, about 40cm or so.  Half of the balloon was gone but it is also clear that the other half retained the shape of the balloon.  That is cool.

I think I need a couple of flash guns, or at least, I need to use a reflector to get more light on the right side of the balloon.

Well, this has been a good test.  Now, I know for sure the circuit is fast enough to capture a popping balloon.  I just need to play a bit with the light now.

I have a wild idea of shooting firecrackers.  Darn, the Lunar New Year just passed.  Hmm... I think I have to wait until Canada Day.

Sound trigger for high speed flash photography, part 5

So, it's easier said than done.  My balloon pop test shows that my circuit is too slow or that sound does not travel fast enough--the microphone was positioned about 2.5 metres away.  The flash gun was positioned about a metre away.

Let's see.  Sound travels at 340 m/s.  To cover a distance of 2.5m, it would take 0.0074s or 7.4 ms.  Maybe the balloon collapses faster than that?

Well, I just wasted one blue balloon.  Fourteen more to go.

Blue balloon pop

Sound trigger for high speed flash photography, part 4

My fingers were itchy.  I wanted to find out how good the sound trigger really is.  My first attempt with the flash gun did not work too well.  The flash fires off only with a really loud hand clap or an air blow onto the electret microphone.  I had to replace the PN2222A transistor I used with the OptoIsolator I used with the laser trigger circuit--it looks like, although I am not sure why, the Base of the PN2222A may need to be driven by at least 3.8 volts or higher current but the circuit could muster only 2.5 volts or so and about 3 mA, but about 2.5 volts is enough to activate the OptoIsolator.  With the OptoIsolator, a finger snap can trigger the flash gun to fire.  After I got the flash to fire, it was time to look for some target to shoot.

I remember seeing a couple of bags of balloons at my place a few years ago but cannot find them anymore.  Perhaps they were used up for weddings and birthday parties.  Balloons would be really cool I think, but there was none around.  I had nothing cool to test the sound trigger with.  I decided to test with a marble and a column of Mega Blok blocks.  I am unimpressed with the capture but it shows how good the sound trigger worked.

The marble hits the column of Mega Bloks pretty hard--I used to play with marbles and a flicker of the thumb sends the marble off pretty fast and hard.  One can see in the photo below where the column broke and how the top half stayed fixed while the bottom half started to move by a millimeter or so.  So, the sound trigger worked quite well.

Marble and Mega Bloks

I think the Dollar Store sells those balloons.  If I have time tomorrow, I will grab a few balloons to try out.

Sound trigger for high speed flash photography, part 3

The beauty of a potentiometer!  Well, with the circuited powered up, I adjusted R5 from 1 MOhm down to 0 Ohm to see how sensitive the circuit is to sound.  I initially thought that a higher resistance in R5 would give higher amplification.  It looks like it's the reverse--the smaller the resistance, the more sensitive the circuit is. At about 250 KOhm, it seems to work quite well.  I was in fact able to detect the plop of a water drop a few times.  I think I will wait until Friday night when I have more time to play with it and when I stay up until the cars sleep.

Again, C2 was removed from the circuit.

Having played with the circuit over the last few days, I am starting to wonder now though, whether a sound sensor is the best method to use for detecting water drops.  The sound a water drop makes is so faint that it might as well as part of ambient noise.

Sound trigger for high speed flash photography, part 2

Though still not perfect, my circuit is getting a little better.  I removed the second capacitor (C2) from the original circuit design.  The new design can detect slight air vibrations (e.g. when I blow on the electret microphone) and softer sounds (e.g. light finger snaps).  Water drops cannot be picked up still however, although I can hear the plop that it makes.  I guess it is just a matter of increasing amplification.

Now, the idea behind the LM324 op-amp that I am using is this:  the op-amp amplifies the voltage difference between the V+ input pin and V- input pin.  (See:  http://en.wikipedia.org/wiki/Operational_amplifier.)  The V+ input would be used as a reference voltage.  The V- input would be fed from the electret circuit.  Increasing the resistance of R5 or decreasing R2 should increase the amplification.

I have tried decreasing R2 to zero but it does not seem to change the sensitivity of the circuit--from my visual observation.  R5 is already set at 1 MOhm.  Maybe I can get a 10 MOhm resistor and see what happens.  Intuitively, increasing R5 would allow more current to flow to the output line and less to the V- input line (i.e. the negative feedback).  Similarly, decreasing R2 would allow more current to flow into the V- input pin of the LM324.

I will see if I can find some time to swing by my local electronic store to pick up a 10 MOhm resistor some time this week.

Sound trigger for high speed flash photography

I did not design the following circuit:

http://i.stack.imgur.com/XJa21.png

I did not follow it to specification either.  For this circuit, I bought an electret condenser microphone ($1.50), an LM324 op-amp ($0.70, instead of the LM741), and 0.47 uF polarized capacitors ($0.20 each).  Also, instead of the 100 KOhm resistor, I used a 1 MOhm potentiometer ($0.70, set at 1 MOhm for higher amplication).  Instead of the 10 KOhm resistors, I used 6.8 KOhm resistors.  Instead of the 2.2 KOhm resistor, I used two 1 KOhm resistors.  The output of the circuit is then fed to the base of a PN2222A transistor that will trigger the flash gun.  The purpose of the circuit above is to amplify the voltage signal created by the electret microphone.

Well, my first attempt was not very successful.  Yes, the electret microphone seems to work.  (I read somewhere it generates a range of only 14 mV, hence amplification required.)  However, the circuit is not sensitive enough.  I am able to trigger the flash gun by clapping my hands only.  Snapping my fingers does not produce strong enough of a voltage to trigger the flash gun.  A water drop will produce a lot softer sound, so there is no way that this circuit will work for me.  Well, I gotta do some more thinking now....  I am also thinking whether I should just buy an electret audio amplifier from eBay for $4.25, although, I do not know if they are sensitive enough either.

Reference:

• The circuit above came from http://electronics.stackexchange.com/questions/16529/why-is-microphone-opamp-arduino-circuit-not-working
• Parts of an electret microphone
• How to use an electret microphone
• Basic powering information on electret microphones