Singing Munks -- a sequel

rjo_

Guys...

I was furtively putting the sample circuit from OldBitCollector's cookbook together when Heather got hers working...

Then I looked at the circuit a little and couldn't figure out why the capacitors would be needed for plain audio out...

So I took them out... and it still works. I was left with just a 100 ohm resistor between my Prop pin and the inside terminal of the RCA connector ...I was afraid to take the resistor out... my fear of frying[noparse]:)[/noparse]

Is there a good reason to leave the resistor in there?




Rich

rjo_

oops... that should be

"Guys and Gals"

sorry

Bergamot

We have gals?

rjo_

Came as a shock to me too!... unless Heather is really Heath. I would expect that in this crowd[noparse]:)[/noparse]

rjo_

Heather is probably too young for me... but if there are any 40+ female engineering types out there............

rjo_

But really... back to resistors. Do I need it... if so, why. No BS allowed.

Oldbitcollector (Jeff)

(Preface: NOT from an ee)

I suspect the caps are using to boast the strength a bit, so I'm not surprised that works.
(Should have tried that myself.) <EE's please speak up>

But as for the resistor, I don't think I'd remove that. Even lightweight headphones can
act as a microphone, perhaps sending a little power in the wrong direction.

I'll do some testing on my end too and update the PropellerCookbook to include this
little piece of information as YMMV.

Oldbitcollector

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The comments and code above are proof that a million monkeys with a million propeller chips *could* write Shakespeare!

rjo_

Thanks bunches.

Rich

Graham Stabler

The capacitor and resistor form a filter converting the rapid pulse train coming out of the propeller into an audio signal. The two components create a potential divider that is frequency dependent, tending to short higher frequencies and pass lower ones.

The fact it still works is probably because of the low bandwidth both electrical and mechanical of the speaker system (and your ears) so that in effect you are still doing the filtering, that or parasitic capacitance is enough. Put the same signal into a scope and you will see lots of pulses.

Resistor is probably worth it just to be on the safe side, it would depend to what you were connecting it to specifically and how that was designed.

Graham

OwenS

Remember that most amplifiers capacitively couple the input into their amplifying device, be it a OpAmp, discrete Transistor circuit or Vaccuum Tube.


So the HPF is now likely between the resistor and the Hi-Fi's capacitor

Graham Stabler

Its a LPF that you want and that would not create one, all it does is cut out the DC.

Graham

rjo_

I'm trying to hack together a geomagnetic NMR application(around 1.3 khz) so it's clearly in the audio range[noparse]:)[/noparse] ... I do have the signal going into an Amplifier... haven't measured anything yet. Just worried about the health of my Prop... I'll leave the resistor in[noparse]:)[/noparse]

I'm going to have a lot of "dufus" level questions.

Thanks guys.

Rich

Harley

Rich,

Googling, find that research is being done around a much higher level than what the Prop can provide. On design generates a high magnetic field (800 MHz, 18.8 T) for a NMR spectrometer.

I'm wondering what super sensitive gizmo you'll be using to sense anything. Not putting down your project. Just highly curious what can be observed at so low a freq. Thanks for any details.

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Harley Shanko
h.a.s. designn

rjo_

Harley,

Love your posts, this one in particular... AND I am accepting suggestions.

http://www.enc-conference.org/longabs/E070287.3500VER.1.pdf

This reports full imaging at 46 microTesla (.46 gauss)... the "trick" is a pre-polarization pulse of 1 gauss and an effective voxel of 27 cubic millimeters, the sensor is a SQUID magnetometer...

I'm just trying to get a single FID out of this thing... so I can conveniently use less sensitivity by increasing the effective volume. There are all kinds of things that I don't understand... and one thing that I do: NMR theory is intellectually bankrupt... I got that from the authors. So what is possible... and what is predicted are "radically" different species.

By the way... did you ever wonder why EEG's use a cut-off filter? There is a lot going on around 1MHz... and no instruments to watch it!!!

Rich

Harley

Thanks Rich for the info 'overload'.

(An old friend once wrote me the info I sent him was 'more than I ever wanted to know about that subject'.)

I looked up the URL referenced. Way out of my field, for sure. But sure would like to get images 'at home' like shown. Sure would like to have such imaging capabilities.

What sort of sensor do you have/plan to design/buy? I have no idea what a SQUID is or where to obtain one.

Keep us informed of this project.

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Harley Shanko
h.a.s. designn

rjo_

Actually... I was hoping for help from the radio guys... A squid is basically a point sensor... the field being generated occupies the entire near space... ... and it is a field not a photon (trying to put proper limits on field/photon theory ... while I'm at it[noparse]:)[/noparse]