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Old Jan 06, 2015, 04:36 PM
Director of Entropy
EarthMagnet's Avatar
Joined Jul 2012
47 Posts
Quote:
Originally Posted by Simon Castle View Post
Sounds like DC coupling problems, stick a cap before the input, or possibly between pin 3 and the pot, hope it helps.

You do have a common ground dont you ?

http://web.mit.edu/6.s28/www/schematics/lm386.htm

... Simon
I do have common ground and I tried with the cap in between the 9V input and the amplifier input and got the same results. I'm not sure what cap to use though, I harvest them out of old electronics from the thrift store, so I tried just about every one I had and no luck.

Any thoughts on how to make it work with a speaker?

I'm not sure I want to use the LM386 amplifier anyway, it seems to amplify the static volume in between the vario tones too, which is extremely annoying. I might try to have the software put out a "no tone" signal in between beeps to eliminate the static, we'll see.
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Old Jan 07, 2015, 12:47 AM
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Norway, Vestfold, Larvik
Joined Jun 2012
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Would it not be enough with a single transistor or something on this?

I have tried the module on a small speaker directly, and I can hear it.
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Last edited by hotvedt; Jan 07, 2015 at 12:55 AM.
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Old Jan 08, 2015, 08:49 AM
Director of Entropy
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Joined Jul 2012
47 Posts
I've discovered the purpose of the 3.3 and 33 uF capacitors on the plane side circuit. My understanding of electronics is very basic, but it seems they act as a filter or voltage smoother. I first built the circuit without them, and was getting a lot of static feedback in between vario tones (i.e. "crunch crunch crunch *beep*, crunch crunch crunch *beep*").

When the software isn't transmitting a beep (like when the air pressure is stable), it's not transmitting anything so I would just get static, probably from the power source. This became a problem when I hooked up an amplifier circuit (LM386) to the ground station, since the amplifier tries to even out the volume no matter what's being received but with some lag. So it would boost the volume for the static, then output a very loud beep that would get quieter. The caps seemed to have solved that.

I think I've also sorted out the ground station amplifier circuit and will post the diagram once I've figure out why it works.

If I'm mistaken in my understanding of the circuit, please let me know. I want to learn how this stuff works.
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Old Jan 19, 2015, 06:04 PM
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Thanks a lot KK!
Raining outside those days, anyone to report FS1000A TX range Vs voltage?
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