Reflective Opto RPM Sensor

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labview1958
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Reflective Opto RPM Sensor

Post by labview1958 » Fri Aug 26, 2005 11:36 am

I have attached a copy of my reflective opto rpm sensor circuit. The output is sent to a Ni-6025E DAQ card. Is my signal TTL?<p>Image

Robert Reed
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Re: Reflective Opto RPM Sensor

Post by Robert Reed » Fri Aug 26, 2005 1:12 pm

The 220K for the LED is way too high. Maybe 220 ohms?
Also The 100K load will slow down the out put speed. Don't know how hi an rpm you want to count, but if you have problems, reduce this value.

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Re: Reflective Opto RPM Sensor

Post by Gorgon » Fri Aug 26, 2005 2:52 pm

Hi Labview1958,
I agree with Robert on the LED/ transistor issue. The output you ask about is not TTL. To be honest i don't really know what you get out of that. I suppose it is some form of pulstransformer you use? By looking at it I would assume that you get some form of bipolar (+/- around 0v) output. Connecting this to a TTL input, may not be healthy for the input. Why do you do it this way? Please explain the background for this. <p>If your +5V and GND is taken from the 6025E you don't need the output-transistor (or the transformer), just connect the output from the comparator,with the pullup(1k to +5V) to the TTL-input.<p>TOK ;)
Gorgon the Caretaker - Character in a childrens TV-show from 1968. ;)

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Edd
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Re: Reflective Opto RPM Sensor

Post by Edd » Fri Aug 26, 2005 4:23 pm

With the supplied information of your application, how about using this interfacing for input to your system.<p>www.princeton.edu/~mae412/SCHEMATICS/op ... chmitt.pdf <p>TTL compatible …with no speed / frequency encumbrances as per your incorporating of a transformer onto your circuit. Just trim the illuminator LED current to your required needs….no femtoampere current starving…as per your 220k(typo!) unit.<p>73's de Edd
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:D<p>[ August 26, 2005: Message edited by: Edd Whatley ]</p>

Robert Reed
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Re: Reflective Opto RPM Sensor

Post by Robert Reed » Fri Aug 26, 2005 5:26 pm

Labview
I too have had the idea of building an optocoupled tachometer in the back of my head for a while. I guess your post jiggled it lose, and now I'm thinking about it again.
What opto device are you using?
What is the expected pickup distance (in inches)?
Where will you purchase reflective tape?
Since you have probably already researched this, I thought your reply might save me some time.
And also, I too am curious about the output transfomer--are you coupling into some sort of incompatable circuit?

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Chris Smith
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Re: Reflective Opto RPM Sensor

Post by Chris Smith » Fri Aug 26, 2005 6:03 pm

Reflective tape can be found in hardware stores under heating and refrigeration supplies. <p>Its a thick shiny aluminum foil about 25 thou thick, and it has a sticky backing to it more like super glue than duct tape. <p>Much like duct tape it is used in hot and cold joints in central air ducting.

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Re: Reflective Opto RPM Sensor

Post by Yerry » Fri Aug 26, 2005 6:13 pm

Why would you want an optocoupled tach in the back of your head?

labview1958
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Re: Reflective Opto RPM Sensor

Post by labview1958 » Fri Aug 26, 2005 7:56 pm

The circuit was made by someone, I believe who is good in electronics. The purpose is to find the rpm of a rotating disc by the reflective method. The output signal is supposed to be a TTL. It is fed into a COUNTER of a NI-6025E DAQ card. There the frequency is found by a labview program. My friend is on leave. Should I take out the transformer? What use is the transformer?

labview1958
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Re: Reflective Opto RPM Sensor

Post by labview1958 » Fri Aug 26, 2005 8:38 pm

My friend base his drawing on this:
http://www.iuma.ulpgc.es/users/jrsendra ... ptores.pdf<p>Robert Reed: The main problem is not the reflective part but the absorbtive portion. The reflective part, you just can buy the aluminium tape but the non-reflective part? How?

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Re: Reflective Opto RPM Sensor

Post by Robert Reed » Fri Aug 26, 2005 9:37 pm

Labview
The tapes in question are just for test standards. This determined the opto output when lit (relecting) and when dark (not reflecting). You would normally use only shiny reflective tape in your rpm tests. However ,if the test object were a very shiny surface already you may need to switch to a "dark" tape (electricians tape) to extinguish reflection. Results will be the same. As to the transformer-ditch it- this was somebodys wet dream.
Replace it with a resistor of a few K's again depending on desired count speed. You may be able to go directly off of the comparator instead but I'm not sure of the voltage swing at that point. Getting late and I'm too tired to calculate it.
The opto you show has a very shallow focal point (<0.25"),wouldn't work for me as I need 3" to 4".
Anyone out there know of such a device?
Yerry
Because the contact tach I've been using was causing excruciating pain in my cranium.

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Externet
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Re: Reflective Opto RPM Sensor

Post by Externet » Sun Aug 28, 2005 11:42 am

Hello labview.<p>If your circuit is meant to be read on some frequency counter, you have a RPS tachometer (which is fine with me), not a RPM.
Most old fax machines / copy machines have tiny reflective optocoupler modules to sense the presence or not of paper, with logic level output. Already made and very canibalizable.<p>Miguel
- Abolish the deciBel ! -

labview1958
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Re: Reflective Opto RPM Sensor

Post by labview1958 » Sun Aug 28, 2005 11:54 am

Here is my revised circuit. Can it work?<p>http://img175.imageshack.us/my.php?imag ... or28hd.png

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Re: Reflective Opto RPM Sensor

Post by Gorgon » Sun Aug 28, 2005 1:08 pm

Hi Labview1158,
The circuit looks good now.(It is depending on the quality of the optical components) The output of the comparator equals an open collector output and is TTL compatible.<p>You should also connect the +5v to the daq board pin 34 or 35, this makes the circuit selfcontained with no external connections and possible noise sources.
Add a 10uF and a 0.1 uF capacitor over the supply voltage. (+5V to GND) for decoupling. <p>TOK ;)
Gorgon the Caretaker - Character in a childrens TV-show from 1968. ;)

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Edd
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Re: Reflective Opto RPM Sensor

Post by Edd » Sun Aug 28, 2005 3:05 pm

Aaa haa.... dribbling in of a bit more pertinent info, as per the referenced Sr E.S. Sendra…. a la Canary Islands…no less.<p>If you take note, the referenced application note is mainly concentrated on information relevant to an application of detecting of rather slow event occurrences.
E.g. detecting…a mechanical limit - paper sensor - position sensor - level indicator - coin detector.
All of these not necessarily being fast repetitive events. This would be more in line with (Schematic on page 2 fig 4) the inductive load on the ‘3053 collector circuit being a driver solenoid of an electromechanical counter circuit… or a bell/buzzer/chime if an aural indication was need instead/in conjunction with a count.<p>Looks like your final schema will fly, excepting.
The detector input needs to go into the – input (4) of the comparator while the reference v/div bridge feeds into the + input (5)…also put a noise suppression bypass capacitor .01 ufd across the 100k supply resistor.
If in the end, you find the TTL output a bit low in amplitude, you may have to incrementally scale up the 1 K output resistor in value.
Refer to page 4 figure 11 if you have to “tweak” sensitivity.<p>Final point is if that you just happen to be referencing that series of optical switch unit in the Da Da sheet, but have not yet bought a unit…and are acceptable to the type of construction that I have specified below for RR …..you would want to be using the slotted detector version shown on page 5 and photo fig 12…read text at top. If you select the 304-560 version…behold all of your interfacing problems is solved with the complete package built inside … as per fig 13 (right half).<p>
Ruh-Ruh:
[[[ The opto you show has a very shallow focal point (<0.25"),wouldn't work for me as I need 3" to 4".Anyone out there know of such a device? ]]]<p>In my last application, I made my own custom unit. If you will tear into the typical optical interrupter module…. which an object passes thru to interrupt its beam….. you are going to find the separate xmit and rec units that can be readily extracted. They are typically built as thin small rectangular blocks with mini lens molded on above the sensing/output portions. Usually the lens o.d. is 1/16 in or 1/8 in absolute max. A piece of thin wall tubing is selected to cover the lens of each component individually, of your option on length….one inch max in my case. Epoxy fused the tubing to the adjacent lens surround. The tubing was int / ext painted flat black to negate ext/adj lighting aberrations. Pieces of rigid wire are telescoped inside the tubing’s and are of such length that their crossing will establish the focus locus alignment of the two elements. BTW that available “alignment” wire happened to be “baling wire” in my case. 10 feet affixed between a rigid post and auto bumper and s-t-r-e-t-c-h-e-d out an additional 4 inches to leave some STRAIGHT wire to be cut down. Had I needed your focal point of 4 inches the separation of those optical elements would have been a mere ½ inch. Even less spacing for more distant locii. Proper crossover alignment was established with the wires and then one unit was was epoxied in place onto a narrow bakelite blank.
After set up the second unit was positioned and held in crossover alignment with modeling clay while the epoxy was applied. Should you need a variable / changeable focus the second unit could be mounted upon a lead screw adjustable / pivoting skid.<p>The whole assembly results in a very noise free operation due to its shielding of ambient /stray light. The only enhancement to be acquired over using a 1 inch white stick on target ( Contact paper or Meads white stick on 1 in dia circles) was using a flat black one with a ¼ in white stripe centered within it.<p>
73's de Edd
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:D<p>[ August 28, 2005: Message edited by: Edd Whatley ]</p>

Robert Reed
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Re: Reflective Opto RPM Sensor

Post by Robert Reed » Sun Aug 28, 2005 5:16 pm

Edd
Not meaning to look a gift horse in the mouth (your suggestion), But -two questions:
Is it possible not to have any particular focal point? I would like to operate this as a handheld probe at distances of 2" to 4" , as circumstances dictate . <p>Would this device have enough sensitivity to run the 8" path that may be required of it (4" out;4" back)?

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