Need help finding an encoder wheel

[echo]

I am converting a drapery motor from a mechanical limit switch to electronic
and require one of those slotted wheels about 1.5 inch in diameter so I can
use a LED / photo-transistor interrupter module. I had planned on using a
hall effect switch but finding a magnetic disk is even harder. Optical will
also be very high resolution compared to hall.

As the motor spins the slotted wheel will pass through the detector and give
me a stream of pulses. I plan to use a 555 or similar to detect the pulse
widening as the motor slows at the end of the drapery pull or in a jam
condition.

Mice with balls have such a wheel but they are too small for my application.
Anyone know of a product I can find in a junk bin that would have an encoder
wheel ? VCR maybe.

 

[PeterD]

I am converting a drapery motor from a mechanical limit switch to electronic
and require one of those slotted wheels about 1.5 inch in diameter so I can
use a LED / photo-transistor interrupter module. I had planned on using a
hall effect switch but finding a magnetic disk is even harder. Optical will
also be very high resolution compared to hall.

As the motor spins the slotted wheel will pass through the detector and give
me a stream of pulses. I plan to use a 555 or similar to detect the pulse
widening as the motor slows at the end of the drapery pull or in a jam
condition.

Mice with balls have such a wheel but they are too small for my application.
Anyone know of a product I can find in a junk bin that would have an encoder
wheel ? VCR maybe.

I don't get good vibes from your technique. It seems to be loaded with
hidden pitfalls and problems, and will be a complex circuit.

I'd suggest monitoring the motor current. When current rises to a
preset limit you know you are either at the end or the thing is jamed.

 

[JeffM]

..

Try a male Nutria, perhaps?

....or, if you don't like orange teeth
--or REALLY need to scale up the resolution:
http://www.google.com/images?q=Capybara
http://www.google.com/search?q=largest-extant-rodent+-rodent-family+-rodent-in

 

[echo]

Peter, current monitoring sounds like a good idea. If it's able to detect a
freewheeling condition of the motor, it might be the best option.

What sort of device for a 120VAC would you use. The motor has 2 windings so
it can spin in both directions. I suppose whatever device could be placed
in the common leg.

David

 

[PeterD]

Peter, current monitoring sounds like a good idea. If it's able to detect a
freewheeling condition of the motor, it might be the best option.

What sort of device for a 120VAC would you use. The motor has 2 windings so
it can spin in both directions. I suppose whatever device could be placed
in the common leg.

David

First, I'd strongly suggest not top posting (I've fixed this reply).

Second, an A/C motor that is reversable usually (strong usually)
consists of a run winding and a start winding. The polarity of the
start winding is reversed on startup to make the motor run the
opposite direction.

Some motors (usually smaller ones) the start and run windings are in
the circuit all the time (using a capacitor in the start windings to
generate a phase shift), and some the start winding is switched out
with a mechanical switch (usually higher powered motors)

WIth either of these setups you'd monitor current in the run winding.

With an A/C motor you do have some issues with current measuring
(unless you know exactly what you are doing, don't directly connect to
the A/C side, instead use a current transformer or a magnetic field
detector (can be built from a hall effect trasnistor).

 

[jasen]

As the motor spins the slotted wheel will pass through the detector and give
me a stream of pulses. I plan to use a 555 or similar to detect the pulse
widening as the motor slows at the end of the drapery pull or in a jam
condition.

Mice with balls have such a wheel but they are too small for my application.
Anyone know of a product I can find in a junk bin that would have an encoder
wheel ? VCR maybe.

ISTR some Meccano(tm) parts with a circle of 1/8" holes...

alkternately:

an ABS sensor setup - magnetic rather than optical but on about the right
scale for your task.

have you considered detecting the increase in current to the motor as it is
slowed instead?


Bye.
Jasen

 

[echo]

I am looking into current sensing using a hall effect transducer as peterd
has suggestted.

It is quite hard to come up with a device that will give a 0-5volt output
with a current of say 0-15amps in a linear fasion. I'm going to try a few
experiments with a toroid with a slit to accept a hall sensor. I'll try
wrapping the leads of the circuit under test around the toroid a few times
to get good saturation of the toroid.

 

[echo]

so windings

Sorry for the top posts - it is a habit that I learned long ago, thinking it
made more sense to get the fresh meat at the top so readers did not have to
wade through the old posts unless they wanted to. I guess I was wrong. I
hope it is not against the boards etiquette to post pics. ASCII diagrams
look like crap.

I've redone most of the attached diagram. The original was a thermal fax and
was degraded badly. I could not tell if the motor windings are supposed to
be joined in the center or not.

I bought a small toroid and a hall sensor so am going to cut a slit in the
toroid and insert the hall. Hopefully I can come up with a useable current
sensor. The commercial ones I've seen are large and $$. I'd like to have a
circuit that gives an output of 0-5volts representing the current 0-15 amps,
give or take. Then I suppose I'll need a PIC chip to measure the analog
voltage and be able to make some decisions based on the current. There
might be a simpler way without a PIC, maybe a 555, but a pic would offer
more options.

My questions are:
1 - okay to monitor the current just to the left of SW1 ?
2 - any commercial sensors at less than extortionate prices ?
2 - simpler setups without a pic ?

Update:
Learned of a family of current sensors by Allegro that fits the need for the
current detection. These sensors insert in the circuit directly and do not
need any toroid. They will detect AC or DC current. Cheap !

I need to measure the range of current this motor sinks in each state:
normal, freewheeling and jammed.

Still leaves 2 questions:
Okay to monitor the current on the line side of SW1 on the diagram ?
Is there a simpler solution than using a PIC ?