14 Nov
2008
14 Nov
'08
9:21 p.m.
Hi Folks
Slightly off-topic, but does anyone here know any audio significance of
312.5Hz?
I have here a module from a piece of equipment dated back to 1968. It
consists of a 4-pole, 50Hz motor, a printed disc, a lamp and a
photocell. The printing on the disc (rotor) is a wiggly line of
changing frequency which - according to the disc - represents a signal
between 312.5Hz and 3kHz when spinning at 1500rpm. You light the lamp,
spin the motor, then amplify the signal from the photocell.
I've decided to use this as a tone source, replacing the filament lamp
and photocell with an LED and LDR, or possibly a phototransistor.
What I was wondering was whether end frequencies coincided with any
musical notes.
Cheers
M
--
Matthew Smith
Smiffytech - Technology Consulting & Web Application Development
Business: http://www.smiffytech.com/
Personal: http://www.smiffysplace.com/
LinkedIn: http://www.linkedin.com/in/smiffy
14 Nov
14 Nov
9:45 p.m.
Date: Sat, 15 Nov 2008 11:51:35 +1030
From: Matthew Smith <matt(a)smiffytech.com>
Slightly off-topic, but does anyone here know any audio
significance of
312.5Hz?
I have here a module from a piece of equipment dated back to 1968. It
consists of a 4-pole, 50Hz motor, a printed disc, a lamp and a
photocell. The printing on the disc (rotor) is a wiggly line of
changing frequency which - according to the disc - represents a signal
between 312.5Hz and 3kHz when spinning at 1500rpm. You light the lamp,
spin the motor, then amplify the signal from the photocell.
very cool. do you have somewhere that you could post a picture of this thing? i'd love
to see it!
What I was wondering was whether end frequencies
coincided with any
musical notes.
not in the western equal-tempered scale, anyway.
see http://www.phy.mtu.edu/~suits/notefreqs.html
cheers!
--
.pltk.
9:49 p.m.
well google is saying that 312.5hz and 3khz are important to Russian Low Frequency Radio
Stations... something about timecode.
Date: Fri, 14 Nov 2008 20:42:15 -0500
From: plutek(a)infinity.net
To: matt(a)smiffytech.com
CC: linux-audio-user(a)lists.linuxaudio.org
Subject: Re: [LAU] [Slightly OT] 312.5Hz
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Date: Sat, 15 Nov 2008 11:51:35 +1030
From: Matthew Smith <matt(a)smiffytech.com>
Slightly off-topic, but does anyone here know any
audio significance of
312.5Hz?
I have here a module from a piece of equipment dated back to 1968. It
consists of a 4-pole, 50Hz motor, a printed disc, a lamp and a
photocell. The printing on the disc (rotor) is a wiggly line of
changing frequency which - according to the disc - represents a signal
between 312.5Hz and 3kHz when spinning at 1500rpm. You light the lamp,
spin the motor, then amplify the signal from the photocell.
very cool. do you have somewhere that you could post a picture of this thing? i'd
love to see it!
What I was wondering was whether end frequencies
coincided with any
musical notes.
not in the western equal-tempered scale, anyway.
see http://www.phy.mtu.edu/~suits/notefreqs.html
cheers!
--
.pltk.
_______________________________________________
Linux-audio-user mailing list
Linux-audio-user(a)lists.linuxaudio.org
http://lists.linuxaudio.org/mailman/listinfo/linux-audio-user 
11:01 p.m.
On Sat, Nov 15, 2008 at 11:51:35AM +1030, Matthew Smith wrote:
Slightly off-topic, but does anyone here know any
audio significance of
312.5Hz?
No. But the frequency range you described covers audio telephony.
I have here a module from a piece of equipment dated
back to 1968. It
consists of a 4-pole, 50Hz motor, a printed disc, a lamp and a
photocell. The printing on the disc (rotor) is a wiggly line of
changing frequency which - according to the disc - represents a signal
between 312.5Hz and 3kHz when spinning at 1500rpm. You light the lamp,
spin the motor, then amplify the signal from the photocell.
I'm an amateur radio operator, license VK2LQZ.
What you describe reminds me of a very low frequency RF oscillator with
an audio tone added in. I'd like to see a photograph of the wiggly
line, as I suspect it is not a simple sine wave, but rather the addition
or multiplication of two sine waves at different amplitudes. The
photograph would need to show the angle covered.
A 50Hz motor means a country where 50Hz is common, such as UK,
Australia, and so forth. A 50Hz synchronous motor can indeed do
1500rpm, with the speed controlled by the grid. The voltage would only
control the starting speed, unless there was deliberate air resistance.
But maybe not RF. I've done some calculations. I cannot get 312.5Hz
out of 1500rpm, there's a remainder ... 1500 rev/min is 25 rev/sec, and
312.5 divided by 25 is 12.5, so the audio frequency is not a multiple of
the rotational frequency.
Alternatively, it is an evacuation siren audio oscillator, with a motor
wired to start slowly.
Does it start slowly?
--
James Cameron mailto:quozl@us.netrek.org http://quozl.netrek.org/
11:36 p.m.
Quoth James Cameron at 2008-11-15 13:30...
What you describe reminds me of a very low frequency
RF oscillator with
an audio tone added in. I'd like to see a photograph of the wiggly
line, as I suspect it is not a simple sine wave,
Here are the photos so far, per Plutek's request:
<http://www.flickr.com/photos/msmiffy/sets/72157609086659400/>
I might pull the rotor off completely once I've put penetrating oil on
all the rusty bits - then I'll get a close-up of the entire rotor.
I'm pretty sure that the way that the line is marked would mean that the
tone would run as a sweep between the lower and upper frequencies - and
25 times per second at that. Should be an interesting noise -
especially once it's been fed into a synth ;-)
Does it start slowly?
That I can't tell as I
haven't powered it yet. Think I might replace
the capacitor first - don't know what will happen if I energise a 40
year old capacitor, but don't want my office full of shrapnel.
Rotor spins very freely so I'd guess that it would get to full speed
quite quickly.
Cheers
M
--
Matthew Smith
Smiffytech - Technology Consulting & Web Application Development
Business: http://www.smiffytech.com/
Personal: http://www.smiffysplace.com/
LinkedIn: http://www.linkedin.com/in/smiffy
15 Nov
15 Nov
12:03 a.m.
Date: Sat, 15 Nov 2008 14:06:51 +1030
From: Matthew Smith <matt(a)smiffytech.com>
Quoth James Cameron at 2008-11-15 13:30...
nice to see it... thanks!
cheers!
--
.pltk.
What you describe reminds me of a very low
frequency RF oscillator with
an audio tone added in. I'd like to see a photograph of the wiggly
line, as I suspect it is not a simple sine wave,
Here are the photos so far, per Plutek's request:
<http://www.flickr.com/photos/msmiffy/sets/72157609086659400/> 
7:19 a.m.
On Sat, 15 Nov 2008 14:06:51 +1030
Matthew Smith <matt(a)smiffytech.com> wrote:
Quoth James Cameron at 2008-11-15 13:30...
Fascinating bit of kit. I'd be inclined to try to keep it as complete
and original as possible. I doubt you'd have a problem with the
capacitor. I know someone with a WW2 communications set that still has
almost all it's 'dry' caps, and only half the electrolytics have been
changed.
--
Will J Godfrey
http://www.musically.me.uk
What you describe reminds me of a very low
frequency RF oscillator with
an audio tone added in. I'd like to see a photograph of the wiggly
line, as I suspect it is not a simple sine wave,
Here are the photos so far, per Plutek's request:
<http://www.flickr.com/photos/msmiffy/sets/72157609086659400/>
I might pull the rotor off completely once I've put penetrating oil on
all the rusty bits - then I'll get a close-up of the entire rotor.
I'm pretty sure that the way that the line is marked would mean that the
tone would run as a sweep between the lower and upper frequencies - and
25 times per second at that. Should be an interesting noise -
especially once it's been fed into a synth ;-)
Does it start slowly?
That I can't
tell as I haven't powered it yet. Think I might replace
the capacitor first - don't know what will happen if I energise a 40
year old capacitor, but don't want my office full of shrapnel.
Rotor spins very freely so I'd guess that it would get to full speed
quite quickly.
Cheers
M
7:24 a.m.
Quoth Folderol at 2008-11-15 21:49...
Fascinating bit of kit. I'd be inclined to try to
keep it as complete
and original as possible. I doubt you'd have a problem with the
capacitor. I know someone with a WW2 communications set that still has
almost all it's 'dry' caps, and only half the electrolytics have been
changed.
I have to confess, I do feel an urge to restore it.
I will certainly do preliminary tests (once I've got the thing spinning)
with and LED and a phototransistor, just to see what it sounds like, but
getting a proper setup with the lamp and selenium cell seems like the
Right Thing To Do.
Cheers
M
--
Matthew Smith
Smiffytech - Technology Consulting & Web Application Development
Business: http://www.smiffytech.com/
Personal: http://www.smiffysplace.com/
LinkedIn: http://www.linkedin.com/in/smiffy
20 Nov
20 Nov
10:14 a.m.
Matthew Smith wrote:
Quoth Folderol at 2008-11-15 21:49...
I doubt it'll be a selenium cell LDR, that wouldn't really be fast
enough for 3kHz. What you might find is that it's an early photodiode,
consisting of a thin metal rod for the anode and a C-shaped cathode.
There are special coatings on them, and the current flowing through
changes with the amount of light falling on the cathode. They need
biased to about 150V to work properly, but you should see *some* sort of
output with as little as 9V.
Gordon
Fascinating bit of kit. I'd be inclined to
try to keep it as complete
and original as possible. I doubt you'd have a problem with the
capacitor. I know someone with a WW2 communications set that still has
almost all it's 'dry' caps, and only half the electrolytics have been
changed.
I have to confess, I do feel an urge to restore it.
I will certainly do preliminary tests (once I've got the thing spinning)
with and LED and a phototransistor, just to see what it sounds like, but
getting a proper setup with the lamp and selenium cell seems like the
Right Thing To Do. 
21 Nov
21 Nov
3:28 p.m.
Matthew Smith wrote:
Quoth Folderol at 2008-11-15 21:49...
You can get a combined infrared led/phototransistor in a 'reflective
switch', which could be neater if you do it that way. I'm using the
opb606 for another project, which costs under 1 UKP.
andy
Fascinating bit of kit. I'd be inclined to
try to keep it as complete
and original as possible. I doubt you'd have a problem with the
capacitor. I know someone with a WW2 communications set that still has
almost all it's 'dry' caps, and only half the electrolytics have been
changed.
I have to confess, I do feel an urge to restore it.
I will certainly do preliminary tests (once I've got the thing spinning)
with and LED and a phototransistor, just to see what it sounds like, but
getting a proper setup with the lamp and selenium cell seems like the
Right Thing To Do.
5921
days inactive
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days old
linux-audio-user@lists.linuxaudio.org
9 comments
7 participants
participants (7)
-
andy baxter -
Folderol -
Gordon JC Pearce MM3YEQ -
James Cameron -
Matthew Smith -
plutek-infinity -
sam javor