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Vintage threads from the first ten years

Reed Switch for counter

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4/28/2006 8:41 PM
Dan Gilmore	Reed Switch for counter I just changed over from a mechanical counter to a Red Lion Cub3000. I picked up a reed switch at Rat Shack and it won't keep up beyond rather slow speeds. Can those of you using a similar setup recommend a specific reed switch, ideally with a vendor/part number? Thanks in advance.

4/28/2006 9:06 PM
stan	I use the switch (sensor) from a bicycle speedometer and a 1/2" neo mag. Had to build a de-bounce circuit for the counter, also Red Lion, don't remember the model...eBay special. It seems to be very accurate. Hope this helps.

4/28/2006 9:57 PM
David King	Dan stick with a simple hall sensor or an optical system. Even the best reed switches will have a tough time going over 400 RPM.

4/29/2006 8:42 AM

On 4/29/2006 3:57 AM, David King said:

quote:
"Even the best reed switches will have a tough time going over 400 RPM."

At 400 rpm, each revolution takes 150 milliseconds, whereas even cheap reed switches respond in about one millisecond, so it ought to be possible to use a reed switch at far higher speeds.

The CUB3 electronic counter is inherently debounced, probably enough for a reed switch (or microswitch), but if necessary a small capacitor across the switch will increase the debounding effect.

4/28/2006 10:49 PM
Dan Gilmore	Well, I just fired up the winder after letting the epoxy set on a new neo magnet as the trigger and it seems to count okay, even at top speed (about 1,400 RPM). I had been using a smaller ceramic puck before. This neo is about 5/8" or 14mm and much more powerful. I'll do more detailed testing soon to be sure it is working properly. Guess it wasn't the switch, though.

4/29/2006 5:33 PM

On 4/29/2006 4:49 AM, Dan Gilmore said:

quote:
"Well, I just fired up the winder after letting the epoxy set on a new neo magnet as the trigger and it seems to count okay, even at top speed (about 1,400 RPM). I had been using a smaller ceramic puck before. This neo is about 5/8" or 14mm and much more powerful. I'll do more detailed testing soon to be sure it is working properly. "

A useful test is to disconnect the counter and attach an ohmmeter (set to beep) to the switch, and while rotating the bobbin by hand, see for how much of a revolution the switch is closed.

The CUB3 counter requires pulses no narrower than 5 milliseconds, with no less than 5 milliseconds between them, allowing counting at up to 100 counts/second, or 6000 rpm.

At a more realistic 1800 rpm, or 30 rps, one revolution takes 33.3 milliseconds, and 5 mS is 5/33.3= 54 degrees. So, the magnet has to be adjusted such that the reed switch is closed for at least one sixth of a revolution.

To achieve 6000 rpm, the switch must be closed for half the revolution.

4/29/2006 6:21 PM
David King	Thanks Joe, that explains the problem I was having years ago in a different application, I now see a use for those, kidney shaped, surplus, Ndym magnets from pancake DC motors. I'm vaguely remembering this same discussion from MIMF a few year back. Thanks for straightening me out.

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