Can I do this with a uProcessor?

[Eeyore]

I read it as a -20dB signal is inaudible buried in the 0dB signal
(I.e. "noise *ratio*").

He may have meant ~ 20 dB SPL i.e. his hearing is impaired by ~ 20dB.

Graham

 

[krw]

^^^^^^^^^^^^^^^^^^^^^



He may have meant ~ 20 dB SPL i.e. his hearing is impaired by ~ 20dB.

No, I believe what he said. See above.

 

[Rich Grise]

Rich, "-20 dB" with no units indicator is a ratio between two signals, not
an absolute value. -20 dB referred to a shuttle takeoff at 1000 meters is
still very, very loud. -20 dBm is still a solid signal, about what you get
from a telephone with a soft voiced person. What scale did you really
mean?

I meant "20 dB down relative to a comfortable listening level." At least,
that's what they told me when I was investigating "subliminal tapes",
which were big with "new age" people who believe in psychic healing and
affirmations and such.

But the "new age" seems to have died of old age or something. Oh, well,
another hot idea that went down the dumper. )-;

Thanks,
Rich

 

[Rich Grise]

He may have meant ~ 20 dB SPL i.e. his hearing is impaired by ~ 20dB.

No, krw is exactly right - see my response to joseph2k.

The point is, -20 dB relative to a comfortable listening level is not
noticeable to normal people.

I can't speak for those with hypersensitivity disorder, however.

Cheers!
Rich

 

[Rich Grise]

Have you seen that price for one of these lately ???

I still have a few around, but the wire stripper broke off.

I thought I would be a new one, but $25+ was just too much.

Last millennium, they were quite inexpensive, when everybody was
wire-wrapping everything.

I ground off the rivet on one of mine, took the stripper blade off, and
clamped it into an X-Acto handle, to use wire-wrap wire to do point-to-
point wiring with ordinary solder-type sockets and stuff on VectorBord(tm).

Cheers!
Rich

 

[Eeyore]

No, krw is exactly right - see my response to joseph2k.

The point is, -20 dB relative to a comfortable listening level is not
noticeable to normal people.

I see what you mean now. The simple answer is that a level 20dB below 'background'
(if that's what you meant) may or may not be detectable depending on its character.

A pure tone is *very* audible for example.

OTOH, what's a comfortable everyday listening level. About 70dB ? The idea that you
may not hear a 50dB sound when the 70dB sound is absent is plain mad.

Graham

 

[mpm]

I meant "20 dB down relative to a comfortable listening level." At least,
that's what they told me when I was investigating "subliminal tapes",
which were big with "new age" people who believe in psychic healing

I thought "subliminal" was 6.66dB down.
nevermind.

 

[Rich Grise]

I had to take my Malibu back to Piper in Boca Raton several times for
maintenance. The thunderstorms and humidity were quite impressive!

I used to smoke then. I would go out on a back balcony to enjoy the view of
a small pond lined with trees.

One night I noticed a pair of eyes staring back at me. They belonged to the
biggest alligator I have ever seen. I know how fast they can run, and I
don't mind saying that frightened the daylights out of me.

Then I discovered the door had closed and locked, and there was no way to
get back in.

Fortunately, a waitress decided at that moment to take a smoke break, and
came out on the balcony. I showed her the alligator, but she didn't mind.
She knew all about him. But that was the end of smoke breaks for me

Is that what you were referring to?

The thunderstorms (and resulting electrical disturbances), yes. Never
had a circuit affected by a 'gator, AFAIK.

A story you might enjoy:-

http://tinyurl.com/288q4z[/QUOTE]

Apparently, they have an eminently(imminently?) marketable smile:
http://www.comics.com/comics/pearls/archive/pearls-20070524.html
http://www.comics.com/comics/pearls/archive/pearls-20070525.html

Cheers!
Rich

 

[Jasen]

I'm not familiar with this. What do you mean by scan them at 500Hz?

500 times a second, at 500hz there's room for an 20(ish) cycle debounce
count before the operator will notice that the machine isn't
responding instantly.


Bye.
Jasen

 

[krw]

I thought "subliminal" was 6.66dB down.

Subluminal? ...or is that six feet down?

nevermind.

Indeed.

 

[joseph2k]

Look, he's new to this and frankly his first MCU project doesn't need
keyscanning to save I/O lines and it would likely degrade his background
noise with a nasty buzz.

Graham

Whether or not tempis fugit "scans" in matrix fashion or just checks state
one by one fast enough to be interactive, say "on the measure", all the
switches must be sampled at least 100 times a second. Thus some "digital
noise" is generated.

 

[joseph2k]

The thunderstorms (and resulting electrical disturbances), yes. Never
had a circuit affected by a 'gator, AFAIK.

A story you might enjoy:-

http://tinyurl.com/288q4z



Best regards,
Spehro Pefhany

Google wants way too damn many long lived cookies for this one. Even when i
accepted the damn cookies it was a "no show". Whast a PITA.

 

[Eeyore]

Whether or not tempis fugit "scans" in matrix fashion or just checks state
one by one fast enough to be interactive, say "on the measure", all the
switches must be sampled at least 100 times a second.

Not so much *must be* but 10ms scanning is sensible for an acceptable response
time. You could probably reduce it to 20ms in fact.

Thus some "digital noise" is generated.

Not so. If all the switches are individually connected to port pins with a
pull-up (often internal) , the only transition is when a user presses the switch
itself !

Graham

 

[MooseFET]

Whether or not tempis fugit "scans" in matrix fashion or just checks state
one by one fast enough to be interactive, say "on the measure", all the
switches must be sampled at least 100 times a second. Thus some "digital
noise" is generated.

You don't need to scan unless a key is actually pressed:

Drive the entire RowPort low.
Drive the entire ColPort High.

Watch the ColPort for != 0FFH

Once you know the key is pressed, you can use log2(Rows) steps to
figure out which key. This makes a single small click and not a
buzz. Constant frequencies are much easier to hear than single
clicks.

 

[Eeyore]

Constant frequencies are much easier to hear than single clicks.

This is so true. The background bzzzzz that scanning can create is unacceptable.

Graham

 

[Eeyore]

You don't need to scan unless a key is actually pressed:

Drive the entire RowPort low.
Drive the entire ColPort High.

Watch the ColPort for != 0FFH

Once you know the key is pressed, you can use log2(Rows) steps to
figure out which key.

The penny hadn't dropped earlier but I see what you're doing now.

I'm just wondering if it can be upset by a simultaneous depression of 2 or more
keys.

Graham

 

[joseph2k]

I read it as a -20dB signal is inaudible buried in the 0dB signal
(I.e. "noise *ratio*").

The human ear routinely picks out such signals with surprizing ease and
regularity. A trained ear can dig a signal out from under as much as 40 dB
stronger noise. But in context i do not think that direction that Rich
intended to apply the ratio.

 

[joseph2k]

No, krw is exactly right - see my response to joseph2k.

The point is, -20 dB relative to a comfortable listening level is not
noticeable to normal people.

I can't speak for those with hypersensitivity disorder, however.

Cheers!
Rich

Personally i find 30 dB SPL to 60 dB SPL to be my most confortable range
depending on what else is going on. Just the same i find artifacts at 20
dB below the current listening level to quite noticable and very annoying.
My hearing isn't what it used to be back when i was a teen some decades ago
either.

 

[MooseFET]

The penny hadn't dropped earlier but I see what you're doing now.

I'm just wondering if it can be upset by a simultaneous depression of 2 or more
keys.

You have to take extra steps to detect two keys. Two keys in
different columns aren't the problem because you can look for more
than one low on ColPort. Two in the same Column requires that you
check the RowPort to be sure that it takes on the value you've set it
to.

 

[tempus fugit]

Then again there's ebay ! The 89C52 should do the job IIRC.
http://cgi.ebay.com/5-x-ATMEL-89C52...2QQihZ013QQcategoryZ50915QQrdZ1QQcmdZViewItem

5 of them for $18 !

But then again there's this !

http://cgi.ebay.com/Burner-Free-805...1QQihZ015QQcategoryZ50915QQrdZ1QQcmdZViewItem

It looks perfect for your needs. I'd ask if they can supply a suitable chip
althoiugh if it'll program the Philips 89C51, I'd expect it to do the above
Atmel 89C52 as well

Thanks again Graham - I never even thought to check eBay.