Re: [CAD_CAM_EDM_DRO] Re: Home switch testing?

On Mon, 05 Jan 2004 22:00:42 -0000, you wrote:

>--- In CAD_CAM_EDM_DRO@yahoogroups.com, Harvey White <madyn@i...>
>wrote:
>> On Mon, 05 Jan 2004 05:45:47 -0000, you wrote:
>>
>> >Hi, I just received some slotted opto sensors
>> >that I was planning on using for home sensors
>> >on my retrofit.
>> >This is where I got them from.
>> >
>> >http://www.allelectronics.com/cgi-bin/category.cgi?
>> >category=435&item=OSU-50&type=store
>> >
>> >They have 4 leads on the bottom two are for 6 volt
>> >power + and - and the other 2 are suppost to be
>> >a normaly closed switch wich is disrupted when a
>> >deflective object is penetrating the slot.
>>
>> Well, probably not a switch.
>>
>> >With my obvious limited knowledge about electronics
>> >I tryed to hook the sensor up to test its function
>> >using a couple of D cell batterys a 6 volt powersupply
>> >a small voltage lightbulb and a multytester for electronics.
>> >I have not been able to get this sensor to do any kind
>> >of verifyable disruption yet.
>> >I tested on 2 of the leads was continuety so I figured
>> >this must be the switch side.
>>
>> well, that's the LED, probably.
>>
>> >Testing to disrupt the lightbulb did not work in any of the
>> >various ways I tryed to set this up.
>> >Could any of the more electricly gifted persons please point
>> >out what I am doing wrong here.
>> >I suspect this may not work the way I think it would.
>> >The 2 sensing leads are suppost to be hooked up on 2 pins
>> >of the Parallel port of the PC, have not tryed this yet.
>> >How could I set this up for testing.
>> >
>>
>>
>> Let's give this a try.
>>
>> 1) the thing is infrared, so you won't be able to see it when it's
>on,
>> if you have a camcorder of some sort, or a digital camera, it might
>be
>> able to see infrared, otherwise, radio shack/tandy has a little
>strip
>> that will glow under infrared light, you can use that.
>>
>> the emitter of light is an led. Wire a 470 ohm resistor in series
>> with it, and then ground one end, and run the end connected to the
>> positive end to the +5 volt supply, this will allow about 8 ma to
>flow
>> through the diode. When it's conducting, you can expect to see
>about
>> 1.4 to 1.6 volts or so across the diode.
>

>Is this resistor required just for testing?

No, operation. You hook a power supply up across any diode (LED
included) and you stand an excellent chance of blowing the diode.

>You say to hook it up in series, one end ground and the
>other to +5 volt would this not be parallel hookup.

The resistor is in series with the diode, and limits the current to
approximately (5.0 - 1.6)/470 or roughly 7 ma or so. The LED is just
used as a light source, so it is always on. Going from 5 volts to
ground, you have resistor, other end of resistor that is connected to
+ end of diode (anode), and then cathode of diode (which is grounded).

>Will omiting this resistor prevent it from working?

yes.

>
>>
>> The second part of this is a photodetector. It's basically a
>> phototransistor. One end will be grounded. The other end (plus)
>will
>> go to the +5 volt supply through a 4.7 K ohm resistor. Take your
>> signal to the parallel port from the junction of the resistor and
>the
>> photodetector.
>>
>> Electrically, this is the same as an optoisolator, probably of the
>LED
>> Phototransistor type. Look for specs on the 4N33 or 4N35 chip, then
>> that will give you some hookups to study. The difference here is
>that
>> you can put an object between the LED and the photodetector.
>>
>> Measure the resistance and see if one port changes resistance with
>> infrared... you might be able to use a tv remote to try the sensor.
>>
>> Harvey
>
>Is the purpose of this sensor to pull the pin +5 voltage down?

yes. however, it will only pull down so much current. Within limits,
you can expect to be able to pull down 30% to 100% of the current you
allow through the LED. The LED has a maximum current rating, so you
can't exceed that (7 ma to 15 ma is safe, I'll guess). 30% of 7 ma is
about 2.1 ma, and that's one TTL gate load and about 0.5 ma. The 4.7
K ohm resistor gets you close to that.

>I tryed to connect this side with a Lightbulb wired between the
>+5 volt pin and the ground pin but I could not get it to turn
>on/off while blocking the slot.

Lightbulb wired between the 5 volt and ground pin will not work well.

You have an led wired to be always on. You have a transistor wired to
pull down a minimal amount of current. Block the light, and the
transistor turns off, allowing the 4.7 K resistor to try to pull the
input pin up to 5 volts.

>Also tryed the multytester insteed of the lightbulb it showed the
>5 volt current but it did not alter this voltage durring triggering.

The LED current does not vary, since it is always on. The
phototransistor current will vary, so you can put the multimeter in
series with the 4.7 K resistor, that should show a current change.
You should also see a voltage change across the device output.

>Maybe this is different from just pulling the pin down?

Think that the meter was in the wrong circuit.

>Any simple sugestions for testing this?

Hope that this helps a bit. Please do check the typical use of the
4n33 and 4n35 to see how the chip is likely wired internally, and how
the manufacturer hooks it up.

Harvey