Stumped with Sound

bfgstew

Senior Member
#1
Ok I have been on and off with this for a few weeks now but I still can't get this work how I want it to
I want to activate my flash by a sound input.
I have tried various so called sound trigger circuits but to no avail. The Rev-Ed sound circuit does work albeit very limited but I couldn't get it to trigger the SCR.
I am in the throws of working on this circuit, and I get an output on my scope but no trigger. The output is very sharp and quick, maybe to quick for the SCR, so disconnected the SCR and put the output onto an LED, still nothing!
I just want a simple circuit, hence the LM386, to activate the flash, with a pot to adjust sensitivity so background noise can be discarded, pick up very slight noises or very loud noises. Am I asking to much? Does anyone have a solution? Can this circuit work?

sound.JPG
 

nick12ab

Senior Member
#2
  • Where's your decoupling capacitor?
  • Don't you need a common 0V?
  • What voltage is the output on the scope?
  • How sharp and quick was the pulse?
  • Have you checked the datasheet of the SCR to see if it needs a longer pulse to trigger?
  • Have you tried using a 555 monostable to make the pulse longer?
  • Have you tried using a latch (e.g. flip flop) and a normal transistor?
 
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bfgstew

Senior Member
#3
  • Where's your decoupling capacitor?
  • What voltage is the output on the scope?
  • How sharp and quick was the pulse?
  • Have you checked the datasheet of the SCR to see if it needs a longer pulse to trigger?
  • Have you tried using a 555 monostable to make the pulse longer?
  • Have you tried using a latch (e.g. flip flop) and a normal transistor?
1 - Didn't realise it needed one Nick! What size and were?
2 - Between 3 - 4 volts
3 - approx 1 ms
4 - No, but will look it up (X00619)
5 - No
6 - No

Yes all 0V are common
 
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nick12ab

Senior Member
#6
Check that the SCR actually works by manually triggering it with a bit of wire. Then try the 555 monostable (configured so that it turns on when it receives the pulse then turns off again after a few 10s of ms).
 
#8
Looks like you have enough signal but you have no detector circuit.
Try putting a diode in series with the final output capacitor (after the cap with cathode to cap), increase the 10k resistor on the SCR to 47k.
Put another diode from cap/diode junction to 0v so that the cap is discharged during negative cycles.
Finally, add a cap (maybe 1uF) across the 10k (which is now 47k).
The overall effect will be very similar to the 555 solutions already suggested but will act as a detector rather than a threshold triggered one-shot.
 
#10
Almost, the diode from cap to 0v should be the other way around.
Any old signal diodes will do. I'd probably go for 1N4148 but if you have 1N4001 to hand they will be fine.
Schottky diodes would be better still but don't lose sleep if you don't have any.
 

bfgstew

Senior Member
#11
Doh.......changed diode over now, using 1N4148's and a 1uf electrolitic cap.

Ok, we are getting near now. I can get the SCR to trigger now, but it needs a hefty blow on the mic to do it with the pot set at min resistance, and getting a 2VDC rise in voltage on the scope with a good decay after. How can we improve on this?

Oops, forgot to say to Nick, thanks for the input as usual but BeanieBots idea suited me as I do have the bits needed at hand.
 
#12
You need more gain.
I'm not very familiar with the LM386 so cannot advise above read the datasheet to find out how.
Using schottky diodes instead of the 1N4148's will help a little but not much.
No data on your SCR but you might be able to get a more sensitive one.
Increasing the output cap to 470uF will give a little more drive, but again, not much.
All of the above will probably get you there.
 

bfgstew

Senior Member
#14
I have it on max at moment with the 10uf cap gives gain of 200.

Tried the 470uf cap, but that made it worse. I have no schottky diodes, so will will stick with the 1N4148's for now.

The SCR is pretty sensetive, thats why I chose it, data sheet is linked in early post.
 

bfgstew

Senior Member
#16
The title of this thread is 'Stumped by sound', need to change it to 'Stumped by the bleedin' obvious'
I have been thinking and tinkering with both circuits most of the day, reading and re-reading schematics, data sheets etc, then I had a sudden light bulb moment!
As the saying goes KISS, keep it simple stupid. I neglected to remember that the Rev-Ed sound circuit is only 3v max output and not enough to drive the SCR, so, me being me decides I need BIGGER, BETTER, FASTER...................................wrong, wrong, wrong.
Simply put the output from sound circuit onto an ADC pin, set a level, hits that level, output goes high and triggers SCR that way, simple.
Now need to code it correctly.
Many thanks to those who have endevoured to help me, it's much appreciated.

Stewart
 
#17
Not sure how/why the 470uF cap made things worse?
Anyway, if you now intend to use ReadADC, you might want to consider making the decay last longer.
Keep all the diodes in place but replace the 1uF with something larger (but much smaller than the 220uF). Try 10uF.
 

bfgstew

Senior Member
#19
Well, I now have 2 sound circuits......................YIPPEE.

Both work very well now, but I am tempted to go with my circuit as it only has the 1 pot on it and I am a bit cramped for space.

So a big thank you to all who have helped especially BeanieBots.

Stewart
 

bfgstew

Senior Member
#21
hmmmmmm, stuck again.

Sound trigger works fine when I have the output of the SCR connected to the LED on AXE 091 board, lights every time, no bother.
When I connect my flash via the SCR, nothing happens?
Schematic as in post #9 (diode has been reversed)
SCR is the one in post #3
Any ideas chaps?

Flash unit is 12VDC
 
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bfgstew

Senior Member
#24
OK, now sorted that problem out, simply replaced SCR with an optocoupler and flash fires now.Only now it just seems that the flash is lagging slightly, it doesn't flash as soon as the trigger happens, only fractions, but fractions count.
How can it be speeded up, if at all?

Not rigged up with camera yet as it still on breadboard so I can adjust easily, so unable to really test flash response in real time.

Thanks for your help so far, much appreciated.

Stewart
 

Paix

Senior Member
#25
Trigger earlier. Hippy and Eclectic will loan you their crystal ball over the Christmas break so that you can get in some trigger prediction practice :) Bummer!
 

lbenson

Senior Member
#26
Don't know if it would have, or would, fit the requirements, but here is a nice little adjustable sound detector module which I have been using. $3.58 US.

http://www.ebay.com/itm/New-1pc-Sou...964?pt=LH_DefaultDomain_0&hash=item1e752482ec

There are others. I searched for "Arduino sound sensor". This one just puts out high or low--others also put out a value for ADCing.

This one puts out lots of high/lows (when detecting the sound from my boiler pump). I use the count command to reliably determine the run time for the pump.
 

bfgstew

Senior Member
#27
Nah, they never let their balls out of their sight..........;)

Just realised I can use my scope.................DOH!

Be able to get an accurate reading of the time lag from the microphone picking up sound to the opto triggering.

Get back to you on this, just for info sake.

Stewart
 

bfgstew

Senior Member
#28
Ok, had a go at getting data on oscilliscope about the trigger timings on my circuit. The following is a screen shot of data collected.

trigger test.jpg

It looks like the opto is triggered by the falling adge of the sound output, correct? So there is a bit of a time issue here as I do want it to trigger the flash as close to instantaniously as possible. How can this be achieved?

Thanks

Stewart
 
#34
The 47k/1uF make a time constant so you can't move much from those values.
Even changing to 4k7/10uF will give issues due to the capacitor feeding the output stage.

If you have one to hand, try simply inverting the output with a CMOS inverter (or suitable gate).
Maybe a good old 741 op-amp as an inverter/buffer?
 

JimPerry

Senior Member
#35
The 47k/1uF make a time constant so you can't move much from those values.
Even changing to 4k7/10uF will give issues due to the capacitor feeding the output stage.

If you have one to hand, try simply inverting the output with a CMOS inverter (or suitable gate).
Maybe a good old 741 op-amp as an inverter/buffer?
The circuit is driving a LED optoisolator - 47K for the LED is too high http://www.vishay.com/docs/83725/4n25.pdf - or am I missing something? :confused:
 

bfgstew

Senior Member
#36
If you have one to hand, try simply inverting the output with a CMOS inverter (or suitable gate).
Maybe a good old 741 op-amp as an inverter/buffer?
Not got any of those.

I did read that adding a 100K resistor from pin 6 to 0V can sometimes help, is this the case or are we looking at adding more or different hardware?
 
#38
Ok, bear in mind that we are working with 'what you have'. At some point you will need to consider buying some bits and doing it 'properly'.
Meanwhile, there is one last thing worth trying.
Reverse both diodes on the output stage and wire the opto between 5v and output instead of output and 0v.
That is, pin 1 of the opto to 5v (via 330R) and pin 2 to your detector output.
The sound detector circuit will now need to drive pin 2 low so both diodes need to be reversed and the 47k should pull UP.
If this doesn't work, then I think you will need to consider a completely different method such as the Rev-Ed circuit.

EDIT:
Check (with a 'scope) that the 200uF cap is not reverse biased. If it is, then reverse that as well.
 

bfgstew

Senior Member
#39
I am a complete moron....................

One itsy teeny tiny bit of info I forgot to add to the earlier schematic, is the output doesn't go directly to the opto. It goes to my 28 X 2, does the readadc stuff, when reaches set level another pin goes high which is connected to the opto. I am so sorry if this has confused things, but hopefully now know why there is a slight lag in the output time!??!?!?!?

sound2.JPG
 
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