Hi Chewy,
You have an interesting project. I had not thought about this much before. So here are some of my thoughts.
What are the seals for the holes made from? Rubber? Leather? Cloth of some type? I suppose a bad leak would show up if the pipe were pressurized and a little soapy water was painted around the hole to show bubbles (like checking for a leak in a tire or gas around a piping joint. It is easy to see the soap bubbles form on a leaking gas pipe joint in your home with this bubble technique and the pressure in a natural gas pipe inside your house is only a few inches (<~ 10") of water. ( 34 feet of water =~ 1 atmosphere = ~ 14.7PSI. or ) So 1/3 PSI should be about 27 inches of water and should create bubbles. Add a little glycerin to the soapy water and you have bubbles that will hang around a while (blowing bubbles toy). But maybe this is a little messy!
The eye is very sensitive to light when in a dark room. It is even more sensitive to a strobe light when it well below 10 Hz. Old movies ran at 16 frames per second and you could NOT see the strobe effect. You might think about oscillating/pulsing the light off and on at low frequency. Also, the peak light power can be made higher for a similar heating, as the LED is turned off part of the time. The eye is most sensitive in the green wavelengths, that is why the green lasers appear to be so bright. By the way, 4-6 Amp into a few LEDs seems like an awful lot of power and light... 6A into a 3 volt LED junction would be 18 watts of real power! This is bigger than most LED light bulbs you buy for your house fixtures! They are advertized in equivalent power, which means equivalent to an incandescent bulb. So 18 watts would be the equivalent to about 100-150 Watts. Does one really need to light up the entire flute at one time or just slide the light source up or down the tube and look at each hole individually. If you need circuits to drive the LEDs in a pulsed mode I can probably figure it out for you.
Most of the LEDs that you purchase, whether in strings or individual are already potted in plastic to protect them and sometimes to form lenses. The heat dissipation relies on the copper metal leads to carry the heat away from the pn junction. This is the most important factor for device life... keeping the junction from getting so hot that the elements diffuse to destroy the junction. In the modern strings of LED the semiconductor is bonded directly to a copper metal tape formed with leads. Again, the tape is copper, and is again the electrical lead.
The more modern colorful LEDs emit in the ultraviolet (non-visible blue wavelength region) and the junction area is covered with a phosphor to down shift the wavelength to the visible color, or white, that you choose. (PS. A thought. If you have an LED lamp in a hard to reach location and you just want it to last for ever.... then run it at less than full power.... You will notice the ratings on lights.... 20 years, 25 years, 30 years.... but they never tell you the light output vs those years!? My guess is because it is going down as the junction degrades. After 30 years, you are old and can no longer see well and you think it is your eyes.... but what if the LED lamps are just not putting out as much light! )
By the way, without more information, the LM2596 is probably not the device you want to use to drive an LED. However, people probably abuse it and use it this way. It is a voltage regulator, trying to putout a constant voltage independent of the current load. You want to drive an LED with something that will limit the current to a max or be a constant value (that is adjustable) independent of the voltage output. An LED is a current device, diode, and so the current goes up rapidly with small increases of voltage. So one would prefer to have a current source not a voltage source. A current source measures the current load and tries to hold it constant. The beauty of the LM2596 is that it converts from a higher voltage to a lower voltage and does it EFFICIENTLY by using high frequency switching techniques. While the Amazon add says constant current, I looked up the device spec sheet (
https://www.ti.com/lit/ds/symlink/l...566&ref_url=https%3A%2F%2Fsearch.brave.com%2F ) for the LM2596 and it says it is a voltage source. Unless you have a link to how this device is configured in the board for sale how do you know how to use it to generate constant current? My guess is that it is configured to generate a constant voltage with a maximum current output (i.e. a current limit to protect the device as well as the load). In this regard it might work for you if you are just using this feature... The absolute maximum output current is 3Amps. So the wall wort you use needs to put out more power than the circuit is consuming.
a heating element burning baby oil or equivalent and a little tiny pump sending it into the barrel
If you are also going to be making smoke you might want to check out the liquid that is used to make smoke in model trains. I do no work on these, but have a friend who says that the smoke MUST be non-toxic and is chosen to not take too much energy to form: paraffin oil (mineral oil, or baby oil). Also, do these oils stain a wooden instrument?
I like the idea of using a Magnehelic gauge, but I am a little confused about...
The next improvement is to use a Magnehelic gauge and flow meter sending about 1/3 PSI into
how do you hook the Magnehelic gauge up to the flute so as to tell which hole is leaking?
I worked with high vacuum systems much of my life to prepare thin films. On good systems when you have a leak you connect a Helium detector (mass spectrometer) to the evacuated side and then source a little He gas around the seal that you wish to test and see if it gets into the vacuum system. However, it is a very expensive overkill for what you are trying to measure!
Dave L.
