need advice on making little (baby) explosions

Discussion in 'The Projects Forum' started by JoeLovick, Mar 26, 2006.

  1. JoeLovick

    Thread Starter New Member

    Mar 25, 2006
    2
    0
    Hi,
    So this is probably not your run of the mill electronics project for this forum but i thought it might be worth asking as the proportion of smart people here seems pretty high....

    I am working on a seismology experiment for a graduate class, the idea is to construct a concrete 2d representational cross section through a volcano. every one else is doing a literature review, and as i can barely read the journals without falling asleep, i wanted to do something different.

    So I have constructed a model in concrete, and mounted 24 microphones within the structure. its about 5m wide by 2m high and an inch or so thick, yep its big an' heavy.....

    the plan is to then trigger a small explosions (one for each experiment) and record the first arrival times of the pressure wave as it travels through the model. so I now need to record the audio of each of the 24 microphones.... the scale of the model dictates that we need to record in atleast 44khz and preferably 96Khz, now here comes crunch 1) I only have 6 recording channels, 4 at 96khz 2 at 44khz.....

    so my plan is to make a switching circuit that cycles through the mic's switching each one on and off at preset times after the explosion in the center. time for an admission, the extent of my electronics knowledge runs out after you get to cheap kit amplifiers from radioshack, I have grand plans and lots of enthusiasm but i think it is safe to say i have little clue what i am doing, so here goes nothing....

    I think i can do this using a PIC and a multiplexor, and am working on a design based from what i can gleam from "the art of electronics" which i have checked out from the library, now comes crunch 2) this is that I was going to use a small firecracker to be the explosion, but I realise this will be too dificult to trigger at the right time, and also it is going to be so loud as to saturate the microphones, which are embeded in the concrete..... so does anyone here have any suggestions for an alternative baby explosion source? some one i know suggested blowing up capacitors, but i dont know how practicle that is.... what i need is something that we can trigger from the PIC, and we will then know it takes x milliseconds to detonate, and importantly it will give out a pretty consistent omni direction pressure signal.

    Seperately i have writtent a ray tracing computer model which I am going to use to predict/control when to switch between microphones so we allways catch the first arriving wave form.

    i have no trouble in coming up with a assembler program to control the PIC i do have issues with thinking/planning how and with which components to switch microphones....

    if you think that a little more planning might have been a good plan, you are right, but then wheres the fun in that!

    anyway thanks for reading this and i would love to hear any thoughts or suggestions you might have...

    cheers

    joe
     
  2. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    Hi,

    You're just looking for a shock wave to propagate through the concrete. Bounce a ball bearing off it, vice the explosion. It may not duplicate the explosion pressure wave, but at least it comes from one predictable point. It will also let you figure the rate of propagation through the medium so you can figure how fast you need to switch microphones. Try using piezo sensors next time, and think a bit more about how to conduct the process.
     
  3. n9352527

    AAC Fanatic!

    Oct 14, 2005
    1,198
    4
    Have a look at analogue multiplexer, such as 74HCT4051 (8 Ch) or 74HCT4052 (dual 4 Ch) to switch the signals. Just make sure the signals are within the range (Vcc to Vee) and the switching time is fast enough for your requirement.
     
  4. JoeLovick

    Thread Starter New Member

    Mar 25, 2006
    2
    0
    Thanks I will check them out.... (74HCT4051) that is...

    (beenthere) The reason for not going with the piezo's was because i was advised that they were very directional, much more so than a microphone, and as i want to be able to capture reflected signals as well direct pulses i went with microphones. i have set up a test bed, and can when i have finished the wireing establish the speed through the concrete with a set up pretty much as you describe with the ballbearing, thanks for mentioning it, its a far simpler solution for these tests than i had come up with.

    cheers

    joe
     
  5. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    Hi,

    Piezo's are sort of directional, but I think if you can capture the waveform out you can tell by the initial excursion whether the acceleration was positive or negative. They are also about a buck a pop in the Digi-Key catalog, so experimentation is cheap.
     
  6. transistor_flip_flopper

    New Member

    Apr 10, 2006
    6
    0
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