Re: Need speed switch for DIY funicular/hillside elevator

[Marc_F_Hult <MFHult@xxxxxxxxxxxxxxxxxxxxx>]

On Sun, 29 Oct 2006 17:10:52 -0500, Marc_F_Hult <MFHult@xxxxxxxxxxxxxxxxxxxxx>
wrote in message  <mj9ak21mn3jsgvqivopmac9gjqm7b2tq3h@xxxxxxx>:

>
>On 28 Oct 2006 11:44:25 -0700, astutesolutions@xxxxxxxxxxxxx wrote in message
><1162061065.466027.213040@xxxxxxxxxxxxxxxxxxxxxxxxxxxx>:
>
>>I am thinking of having some way of measuring the outfeed speed of the
>
>On 28 Oct 2006 12:42:24 -0700, astutesolutions@xxxxxxxxxxxxx wrote in message
><1162064544.727178.267460@xxxxxxxxxxxxxxxxxxxxxxxxxxxx>:
>
>>The trick is, how to determine when it is going fast.  I almost need
>>some kind of centrigal device on the cart or at the spool
>
>On 28 Oct 2006 13:55:15 -0700, astutesolutions@xxxxxxxxxxxxx wrote in message
><1162068915.042171.16460@xxxxxxxxxxxxxxxxxxxxxxxxxxx>:
>
>>I'm still at a loss though as to how to easily trigger it on the speed,
>>although obviously a simple solution may be out of my reach.
>
>As far as I can tell, you didn't get an answer to the question you raised
>above despite all the posts ....
>
>It would be straight-forward to make a sensor that would determine the
>rotational speed of the cable capstan(s) and provide a safe/not-safe (go/
>no-go) signal.
>
>One way would be with one or more small magnets attached to the rim of the
>capstan, a hall-effect sensor that would sense the magnet and produce a pulse
>every time a magnet passed by, a frequency-to-voltage converter which might
>be a single IC like http://cache.national.com/ds/LM/LM2907.pdf or a charge
>pump made from a cheap op amp http://cache.national.com/ds/LM/LM324.pdf  and
>a capacitor-resistor network , and a simple comparator
>http://cache.national.com/ds/LM/LM339.pdf (or an op-amp used as a comparator)
>to compare the measured voltage with a threshold set with a potentiometer or
>resistance divider. This c/would cost less than $10 to make with parts from
>Radio Shack. Sounds more complicated than it is.
>
>What you do with the go/no-go signal would be a 'nuther matter.

I looked at your pictures from which it seems that the diameter of the spool
of the remaining cables would vary significantly with amount of cable played
out. So to keep the signal linear with respect to revolutions per minute, one
could mount the magnet(s)on  idler pulley(s).

... Marc
Marc_F_Hult
www.ECOntrol.org