Electronic counter time delay circuit

Discussion in 'The Projects Forum' started by djreiswig, Aug 8, 2008.

  1. djreiswig

    Thread Starter Well-Known Member

    Aug 8, 2008
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    I have a set of CUB5 counters set up on a machine. They are triggered with photo sensors. I am using 24vdc to power everything. I use the current sinking input on the counters.

    The problem I am trying to solve is that some of the items we are counting have areas where the photo sensor can shine through and trigger the counter more that one time for that particular item. There is no practical way to avoid this.

    I would like to try to find a way to only count the item if it blocks the sensor for over a certain time period, probably somewhere in the almost 0 to 1 second range. Probably would initially need to be adjustable, although this could be done with different resistors rather than a potentiometer. I know this is a very small time, but these counters seem to be rather sensitive. (I'd bet they would count a fly if it flew by the sensor.)

    I do have some limited (read very limited) electronic knowledge. If I have a schematic and the part numbers of components, I should have no trouble building it.

    Thanks.
     
  2. bertus

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    Apr 5, 2008
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  3. djreiswig

    Thread Starter Well-Known Member

    Aug 8, 2008
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    I think that is a little over my head. I thought maybe that was something from "Back to the Future", like a flux capacitor. Probably just a fancy name for something relatively simple. It looks like that uses a positive trigger. I think because of the current sinking output of the photo sensor I am using, I would have a negative trigger. Also, it looks like it is a one shot deal. I would need something that would work every second or two. I don't need a very long delay, just enough to prevent double counts.

    This might possibly work, but I don't understand enough about it to know how to hook it up.

    Thanks for the help.
     
  4. djreiswig

    Thread Starter Well-Known Member

    Aug 8, 2008
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    Posted this a while back. Just wondering if anybody is on here now that can help me. I have some more details on what I need.

    I have a set of CUB5 counters set up on a machine. They are triggered with photo sensors. I am using 12vdc to power everything. I use the current sinking input on the counters.

    The problem I am trying to solve is that some of the items we are counting (cooks aprons) have areas where the photo sensor can shine through (neck loop) and trigger the counter more that one time for each item. There is no practical way to avoid this.

    I would like to try to find a way to only count the item if it blocks the sensor for over a certain time period (0-2 seconds adjustable). The time can vary slightly as the conveyor is run with an inverter drive and an encoder. The differential on the good and bad counts is, however, still very large.

    Here are the specifics:
    The sensor to ground readings are as follows. When the sensor is not blocked (seeing the reflector) it is about 10vdc and when it is not seeing the reflector it goes to around .5vdc (that is 1/2) There is a 12vdc power source that is powering the sensor and counter display.

    Here are the components I am using.
    Counter
    http://www.redlion.net/Products/Grou...Docs/01012.pdf
    using input a for my signal

    Sensor
    http://info.bannersalesforce.com/xpe...ure/119223.pdf
    using the white wire for my signal (black wire is not used)

    Here is how I see what the circuit should do:

    sensor reflected
    sensor blocked (main part of apron)
    start counting
    sensor reflected
    stop counting
    sensor blocked for 1.2 (guess?) seconds
    send count pulse
    sensor blocked (neck loop of apron)
    start counting
    sensor reflected
    stop counting
    sensor blocked for .2 (guess?) seconds
    no count pulse sent
    repeat for next item

    I do have some limited (read very limited) electronic knowledge. If I have a schematic and the part numbers of components, I should have no trouble building it. Please be specific with the components information.

    Sorry this is so long. Trying to be very specific so everyone can understand my situation.

    Thanks.
     
  5. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
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    Basically, you are looking to deactivate the switch for a short time after it has been activated once. Look up switch debouncing. Here is a very good reference on the subject.

    Here
    View attachment 4370
    is a 555-based circuit for which you can adjust the "won't switch again" time easily. It is based on an MIT circuit, but unfortunately, I didn't save the original citation. At least, it should give you an idea of how to connect a 555 as a monostable, as mentioned above.

    John
     
  6. djreiswig

    Thread Starter Well-Known Member

    Aug 8, 2008
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    I don't really want to deactivate the switch. I just want to send the signal to the counter after the sensor is blocked for a certain time period. If I deactivate the switch I will miss counts that would block the switch for the desired period if the space between them is not longer than the "deactivated period". I need to have something that will in essence measure the item and only count it if it has a large enough dimension. If it is too short I don't want it counted. (This dimension would be what I would choose by the length of my delay) Over a certain time of being blocked would send a pulse to my counter. Under this time would send no pulse. But the space between the items needs to be taken in to account, so that items are not missed when they are close together. Hence not wanting to deactivate the sensor.

    I posted this question in another forum, and I got a circut that I think does exactly what you say. It didn't work for me. But thanks for replying.
     
  7. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
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    I used the word "switch" to mean the sensor or whatever is driving the counter. The sensor is providing a signal that is either on or off. In that sense it is a switch. A debouncer would take the sensor signal, send the first one to the counter, but not send another until after the time you set has lapsed. John
     
  8. hgmjr

    Moderator

    Jan 28, 2005
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    I can't help but notice there is a function built into the counter called RATE setting. It looks like it can be setup to do what you are looking for. Have you played with that function to see what it can do?

    hgmjr
     
  9. jpanhalt

    AAC Fanatic!

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    Please post the other circuit you have. We may have useful input about it. John
     
  10. djreiswig

    Thread Starter Well-Known Member

    Aug 8, 2008
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    jpanhalt: I don't want the count sent to the counter until after the sensor is blocked for the desired time. It also needs to watch and see if the sensor is unblocked and blocked again during the time. If this happens then no signal should be sent. If a signal is sent when the sensor is first blocked then there is no way to know if the item should have been counted or not (it will have already been counted).

    hgmjr: As far as I know the RATE is like an average display for the pulses in a certain amount of time. This does not count the items persay. It just compared the count to a time and gives an average frequency.

    jpanhalt: The other circuit does as you say and sends the signal right away. I have discussed this a length with another gentleman on another forum, and we have concluded that it won't work. I don't think there is any point in going through it again (too frustrated already) Just wondering if there is something new that this forum can come up with. Maybe my requirement is not possible. That is what I am beginning to think.
     
  11. hgmjr

    Moderator

    Jan 28, 2005
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    After studying the datasheet in greater depth. I came to this conclusion.

    Can you provide us what it is about the circuit that jpanhalt provided did not satisfy your requirements? If we knew where the circuit failed to satisfy your requirement we may by able to make the necessary correction.

    hgmjr
     
    Last edited: Sep 7, 2008
  12. djreiswig

    Thread Starter Well-Known Member

    Aug 8, 2008
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    Okay. Here are two circuits I have gotten off of another forum. Both of them work, but neither does what I want. They both send a pulse to my counter when the sensor is initially blocked. Not what I want. I believe that is what his circuit does also. Not sure as I am not an electronics expert. I have built both of these circuits and I know they both send the pulse right away.
     
  13. thingmaker3

    Retired Moderator

    May 16, 2005
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    Try feeding the sensor o/p to a microprocessor. Have the microprocessor check the sensor every few microseconds. If the signal stays good for the requisite time, have the microprocessor send an o/p to the counter. If signal drops, have the microprocessor reset the cycle.

    This will let you ignore the chef's apron while positively tracking the lawyer's suit. (Or whatever.)
     
  14. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
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    Here's a rough diagram that may help:

    View attachment 4381

    The idea is to count only the aprons, but not the loops. I am not sure they will all be arranged hoop-to-apron; some may be flipped.

    A microprocessor is probably the easiest from a design point of view, but it may be something the OP is not ready to bite off.

    I thought briefly about the design with the CD4017 counter and CD4093 oscillator/logic. I think something like that might work, but didn't look at the circuit very carefully yet. As I understand it, that circuit is supposed to give a single pulse when the sensor is dark for at least a certain number of "clicks." Whenever it senses light, it is reset and the count starts again.

    You say:
    Did you measure the oscillator to be sure the frequency of clicks was low enough? Did the position of the count switch have any effect on that?

    Finally, assume that the circuit referenced above can be made to work. There may be a problem with reliability. That is, false "no counts." We haven't said much about the light or detector. If it is simple, continuous IR, they are susceptible to false triggers. In this case, a false trigger might lead to interruption of a dark period count and a resulting no count. Thus, I think the light/dark detector should use modulated IR, like is used with the numerous emitter/detector modules on the market (e.g. TV remotes).

    John
     
  15. djreiswig

    Thread Starter Well-Known Member

    Aug 8, 2008
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    Your diagram is correct.:D The aprons pass the sensor with the lower end first (all of them) and then the loop. The all go the same way.

    Not sure what you mean by this. Remember my limited electronic knowledge :). I changed the switch positions, and even doubled the size of the resistor so I could better see how it was working. Also, had to put a resistor between the + and counter in terminals to make it count at all. Something with the way the counter unit works. I guess it needs a resistor.

    I am not too concerned with the reliability of the sensors. Many of the machines we have here use this type of sensor and we don't really have any problems with them. The counts are not really critical anyway. If I miss one or two it isn't going to cause a catastrophe. Just using it to track production numbers.

    Can you help me to make this circuit do what I want?
     
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