Calling all electronics experts! - I need some help!

[jdbostrom]

Got a question for you. As I mentioned in my wireless video camera thread, I am planning on equipping my boat with a hydrophone. The sound from the hydrophone will be amplified, then "taken" back to the video camera that has a microphone in it (to transmit sound back to shore). My question is]I[/i] can't think of anything wrong with this idea, but I don't really want to risk the camera unless I have a second opinion (note- you will NOT be held responsible if it doesn't work and ruins the camera . I just want to make sure I'm not missing something really stupid).

Thanks,
Jonathan

[jmw]

Jonathan,

I expect that setup not

Jonathan,

I expect that setup not to work. Thing is that the microphone outputs very small signals and thus is followed by an amplifier whereas your hydrophone signal already is amplified and might thus give far too large signals for the mic's amplifier.
If the amplifier is a seperate one in the camera, I would substitute it's output by the hydro amplifiers one. That should give the best results. Yet I do not expect the camera to have a seperate amplifier.

A very crude and not overly elegant solution, yet a quick one would be to decrease the hydro-amplifiers output using two resistors as a voltage divider and connect that to the microphone wires.
So by now the hydro-output is amplified and then divided and amplified again; neither elegant nor hifi, but it might do the trick.

A voltage divider consists of two resistors]http://www.subcommittee.com/forum/icon_smile.gif[/img]

If it has two wires, there might be a case of a combination wire carrying both supply (DC-voltage) and signal (AC-voltage). If you measure a DC-voltage on the wires, you should use a capacitor between your voltage divider's output and the mic-wire. See what gives good results; might be anything between 100nF and 1uF (as I am by no means an audio expert I have no good values readily available, sorry)
There might also be a different connection setup of the microphone, I am not up to present-day technology.

I don't expect any damage to the camera, yet of course it remains a wee bit tricky. Although I have never heard of one exploding as a result of something like this...

You could of course also mount a speaker close to the camera's mic. Not elegant, no, but hey...
As I don't have a camera, does it possibly have extra inputs?

Hope this helped somewhat,
Jan Martin Wagenaar

[mylo]

Jonathan,

You HAVE to keep

Jonathan,

You HAVE to keep us posted on this. If you can get it to work (I might as well let you make the mistakes .... ), it is definately something I will be putting into my type VII.

Great project.

Mylo

[himszy]

Just out of interest, what

Just out of interest, what do you expect to hear?

Michael

[guillermo pelaez]

Jonathan,

I couldn't agree more with

Jonathan,

I couldn't agree more with Jan Martin, it seems you will have a double amplifier set up, probably saturating the output. Having the schematic for your set up, at least the first amp will help. I would try first to simply twist the hydrophone mic cables to the original mic cables and try the output this way, if it doesn't have the power you want, then an amp set up may be in order, but probably with a gain control (a variable resistor replacing one of your current resistor in the hydrophone amp.

Keep us posted.

Cheers,

Guillermo

[jdbostrom]

Mr. Wagenaar,
Considering the fact

Mr. Wagenaar,
Considering the fact that the camera is tiny ( about the diameter of a quarter and 3/4" deep), I think I might go with the easiest solution, mounting a speaker right next to the camera's mic. Simple, but it should work okay.

Mylo,
I intend to post my progress in my wireless video camera thread.

Michael,
Good question . I guess my 1/72 corvette on the surface, the occasional noisy fish, full-sized boats, etc.



Thanks for the help!

Jonathan



Edited By JDBostrom on 1126991285

[chips]

I have one of the

I have one of the Aquarian hydrophone units, and have used it at a couple of SubRon6 events. It is easier to hear the target models than the subs. I think because the surface model has most of the hull in the air, acting like a speaker cone. Listening to the sub models is harder because they don't resonate sound like the targets.

[jsl]

I think the idea of

I think the idea of mounting a speaker close to the microphone is a really bad one.

I have one of those cameras myself, and the audio quality is miserable, and the audio power is very faint.

I'd recommend a pre-amplified hydrophone signal be fed directly into the microphone wire, through a variable voltage devider and a 0,1 uF unipolar capacitor.

I have not yet done this modification on my own camera, but I seriously doubt that the camera can be damaged from this. At worst it should only distort the image with some horizontal lines.

One other thing to think about. The very first thing that suffers when the signal starts to decay, is that white noise floods the audio channel long before image is lost.

Maybe one should try to transmit the audio signal back to the operater using a small UHF radio. I think they're called FRS radioes in the states and PMR's in europe. Transmission range would be significantly higher, but I have no idea on which audio frequencies such a radio transmits back...

[jsl]

By the way....

Mounting a speaker

By the way....

Mounting a speaker close to the camera might just get the whole thing into resonance, if the preamplifier microphone picks up the sounds that the speaker produces, and then re-amplifies it again.

You know that backbreaking screaming noise one can experience at concerts etc...

[jdbostrom]

Well, I have to say

Well, I have to say that this solution sounds a lot more appealing now after being up late last night trying to get the speaker system to work. When I tested it after finally getting the speaker crammed into the tiny WTC, it didn't work. I'm guessing that the problem was a result of me dripping a little CA glue into the speaker.

Now, does anyone have any simple schematic for one of these voltage dividers? Mr. Wagenaar described it for me, but I'm not so good with electronics and a drawing would really help. Also I will need to know where to put the capacitor.

Thanks,
Jonathan

Mylo- you taking notes of my mistakes?

[jsl]

Find something in the range

Find something in the range of a 22k Ohm logorithmic potentiometer. That's just a "normal" dial resistor not unlike the one in a stereo. Logorithmic just makes it easier to adjust.

The potentiometer has three pins. The two outer pins feature the entire 22kOhm resister at all times. The middle pin is a function of the dial position.

Put the dial in the middle, and the 22kOhm resister is devided in two. 11kOhm from one outer pin, to the middle pin, and the remaining 11kOhm between the middle pin and the remaining outer pin. (adjustable voltage deviders made easy =) )

Connect the pre-amp signal to one outer pin. Connect the other outer pin to ground. Your signal will then be available on the middle pin, at a magnitude depending on the dial.

Connect a 0,1 uF - 1uF NON-polar capacitor to the middle pin, and feed the signal from the other side of the catacitor directly into the microphone wire.

Connect your camera, reciever and something to amplify the signal out of the reciever. Turn up your stereo (or other amplifier) a good bit, and adjust sensitivity on the potentiometer. Adjust until you have a clear audio signal, without crossover distortion, output saturation, "metallic" or "crystallike" sound or amplified noise or radiosignals.

I've toyed a bit a few years ago with a simple microphone pre-amplifier, a condenser microphone and a homebuild adjustable secondary amplifier. The thing was so sensitive, that the condenser mike could pick up breathing 10 ft away in a quiet room, and if the secondary amplifier was turned above some 150 times amplification, the local radiostation chatter could be heard in the headset.

At first I thought some humming noise was picked up from some electrical EM inteference, but it tuned out to be the faint sound of my laptop harddrive made on the other table. Things got much more quiet when I shut it down.

[jmw]

Jacob,

jolly good description! This setup

Jacob,

jolly good description! This setup should work.... or at least give some usable noise.

Jonathan, please let us know what happens and what you''ll be hearing. I am curious as to the results.

Greetings all,
Jan Martin Wagenaar

[jsl]

Try and feed the audiosignal

Try and feed the audiosignal into the stereo amplfier (or whatever you use), both directly from the signal out of the capacitor, and then from the camera reciever box.

Try and get an idea of how much audio quality is lost through the wireless transmission. I'd like to know of your findings myself, as the transmitter circuit is very crude and simple.

[jdbostrom]

Great! Thanks for the help.

Great! Thanks for the help. I will keep you posted (like I said, any progress updates will be posted in my wireless video camera thread).

Thanks again,
Jonathan

[jdbostrom]

Could you do me a

Could you do me a big favor? I am looking for a pot on this site]www.allelectronics.com[/url], but there are so many different ones to pick from that I am completely lost. If you have time, could you tell me what one looks like it would suit me best?

Thank you very much,

Jonathan