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'zero speed indicator'
1998\04\24@004720 by Vic Richter

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I want to use a basic stamp 1 as a zero speed indicator. Acutally, what
I need to
know is when a motor that turns an air lock, at about 15 rpm, stops.
I need to use a proximity switch to send pulses to the stamp. The prox.
switch
will be connected to 12VDC. My question is:
Which would be better....an 7.2V zener diode connected as follows:
prox. switch output 12V.....cathode of zener....anode to stamp
input.....
OR
an opto-isolator.
Seems to me the zener would work just fine. Whats your opinion? Thanks.
Vic

1998\04\24@123551 by Mike Keitz

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On Thu, 23 Apr 1998 23:40:28 -0500 Vic Richter <spam_OUTvicrichterTakeThisOuTspamPOWR.NET>
writes:
>I want to use a basic stamp 1 as a zero speed indicator. Acutally,
>what
>I need to
>know is when a motor that turns an air lock, at about 15 rpm, stops.
>I need to use a proximity switch to send pulses to the stamp. The
>prox.
>switch
>will be connected to 12VDC.

Many of these industrial switches have an "open collector" output that
acts as a switch to ground.  In that case, you could use a resistor to 5V
to pull the output up and make a direct connection.  A resistor in series
to limit any fault currents into the PIC would be a good idea.


If the switch outputs either 12V or 0V, connect it through a rather large
(100K) resistor like the oft-discussed direct RS-232 connection.  The
protection diodes in the PIC will keep the voltage from rising much above
Vdd.

>an opto-isolator.

An opto-isolator would do the job nicely.  It only has much benefit if
the switch's power supply is completely isolated from the PIC power
supply as well.


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1998\04\24@185648 by peter

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Vic Richter wrote:

> I need to use a proximity switch to send pulses to the stamp. The prox.
> switch
> will be connected to 12VDC. My question is:
> Which would be better....an 7.2V zener diode connected as follows:

Sound like you already have the switch(pnp output ?)

I would do this, connect a 330 resistor from your pin to ground
(and a 100n cap) and a 1k resistor to your sensor output


I am also working on a similar system but I am useing a Namur type
proximity switch (two wires 5 to 24VDC, >3ma on current, <1ma off
current)

I connect the + to 5V(I do intend to feed it from a higher voltage
later but 5V seems to work fine with the sensor I have)
and the - to my input pin with a 270 resistor to ground
(and a 10n cap, my motor is not running @ 15rpm)

My sensor has no inbuilt hysterisis so I use a 1K resistor from
another pin (positive feedback) to aviod jitter when stopped.
The sensors range is 5mm and with the feedback I have at least 1.5mm
hysterisis.......works great !!

--
Peter Cousens
email: .....peterKILLspamspam@spam@cousens.her.forthnet.gr  phone: + 3081 324450, 380534
snailmail:  Folia, Agia Fotini, Karteros, Heraklion  Crete, Greece.

1998\04\24@192343 by Stuart Broad

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To interface to proximity sensors that are running on a 12V DC supply I
have been using a simple comparator powered from the 12V supply and
having a pull up resistor from the 5V rail to the open collector output.
Both the 5V and 12V supplies have to be common though so no true isolation
is provided, so this might be a problem for you but that depends on your
application.
Regards,
Stuart.
{Original Message removed}

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