Moderators: Dave Moll, Steve Anderson
DrZarkov wrote:It should work, indeed, and you are not the first one with that idea: http://www.earlytelevision.org/fracarro_30_line.html
Steve Anderson wrote:On a bicycle-logger I built (how environmentally responsible?) I used a small permanent magnet attached to one wheel and a Hall-effect device to count revolutions and thereby work out distance traveled.
It's a solid-state replacement for a reed-switch but available in logic output versions to replace reed-switches as well as linear versions.
They're not sensitive to ambient light or vibration, ideal on an old bone-shaker...I'm talking about the bike.
Worth investigation, they're fast enough for NBTV disc/drum position sensing whereas a reed-switch probably isn't...and of course don't wear out. Hall-effect devices are very common in DC brushless motors to provide commutation information to the controller. They're used in cheap DC fans for PCs as well as VCR head-drum position sensing so they're plenty fast enough.
Steve A.
P.S. A variation on the above., still magnetic and still with the small magnet on the disc/drum. Use an record/playback head from a old cassette recorder, this should produce a pulse as the magnet swings by. No idea on the signal amplitude though...except probably quite low.
Steve Anderson wrote:Harry, here's a very typical place you'll find them on a VCR head-drum assembly. They're the three square chips located at the bottom right of the PCB in the attached picture. Note they're spaced at 30° intervals.
But you may come across some head-drum assemblies that have none, in that instance the controller uses the back-EMF of the motor for sensing.
Steve A.
harry dalek wrote:...i will pull some stuff apart see if i can find some too as you say its worth a try .
harry dalek wrote:I just found out my motor might just have them attached ,its out of a 80s video disc player the record sized type, hooking my scope up to the extra 2 wires i get a sign wave frequency go's up and down with the motor speed .
Klaas Robers wrote:harry dalek wrote:I just found out my motor might just have them attached ,its out of a 80s video disc player the record sized type, hooking my scope up to the extra 2 wires i get a sign wave frequency go's up and down with the motor speed .
I think that is the same Laservision-player motor I use in my monitor. It is a nice motor and the magnetic pick-up gives indeed a nice sinewave from the permanent magnetic ring, a sinewave that can be limited to a square wave. The bad news is: it gives 18 sinewaves per revolution. It took me more than a year to find out how to match the 18 sine waves to the 32 sync pulses. I even thought of remagnetizing the permanent magnetic ring to 32 sinewaves, or if that doesn't work, 16 sine waves.......
At the end I found a way to synchronise the 18 waves to the 32 syncpulses, however it was rather complex and I fear too difficult to describe here.
Klaas Robers wrote:Harry, this motor is designed to run at 25 rev/sec. with the load of a rather heavy VLP-disc of 30 cm diameter. However I think it may run even faster, 50 rev/sec.
The motor runs 12,5 rev/sec on a voltage of about 5 volts.
The trick I used is that I made the genlockable EPROM picture generator and genlocked that onto the incoming video (sync pulses). Then I programmed a pulse signal in the EPROM having 18 pulses per NBTV frame. Those pulses I used to synchronise the motor on with the 18 pulses per revolution. I used the 4046 for that.
The nice thing is that you can program almost every pulse pattern in the EPROM. So the number of pulses per revolution is relatively unimportant.
Klaas Robers wrote:Harry,
my motor is running an aluminium Nipkow disc monitor. If you look at the Convention photo reports in the Gallery of NBTV.org you may see it. It's a square wooden box monitor, normally closed, but at the Convention also shown open.
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