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help connecting 555 timer

Discussion in 'General Electronics Discussion' started by RobertB50, Sep 16, 2016.

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  1. RobertB50

    RobertB50

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    Sep 16, 2016
    Hi, all...
    Im just starting in electronics and I thought being a master electrician would make it easy. Maybe a little? I need help connecting a 555 timer. I have a manual on the 555CN, but it is like 19 pages long! It's more confusing every time I read it.
    First, is it possible to daisy chain a 100 timers. The output of the 1st timer would pulse the trigger on the 2nd timer. The second timer's output would then pulse the trigger on the 3rd and so on. This would go on and on until it reached the 100th timer. I'm not sure if the collective resistance through all the timers would add up to a fatal level?
    All I want is this: When Pin 2 is triggered with 1 second pulse of 2 volts, Pin 3 will send an output of 3 volts or greater... exactly .01 seconds later. This output must last at least 1.0 seconds.
    I think the reset is pretty straight forward.

    Any help would be appreciated
     
  2. hevans1944

    hevans1944 Hop - AC8NS

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    Well, it might help you in preventing electrical fires. :D

    It gets better with some hands-on experience. Keep reading, and re-reading, as you perform experiments on a prototyping board (you do have one of these, riiiigt?) with a single 555 and a handful of resistors and capacitors. Helps to have a logic probe or at least an LED attached to a wire and a 330 ohm resistor to probe the output of the 555.

    Yes, but there are probably easier ways around that barn.

    . You would need to couple each output to the next trigger input with a capacitor.

    Each timer will "do its own thing" without regard to the other timers if the load presented to each timer's output is within an acceptable range. Wow! A hundred of these puppies, huh?

    When used in mono-stable (one-shot) mode, the 555 timer output changes states immediately upon receiving a trigger pulse. It stays in the new state until the time delay has occurred, say 0.01 seconds (10 ms), whereupon the output reverts to the pre-triggered state and remains there until another trigger is applied. Using the word "exactly" to describe the timing of a 555 is a non sequitur. The 555 is not a precision timer.

    The output will last however long you programmed the RC time constant for the 555 to be. When the output goes away (reverts to its previous state, you can use that event to trigger the next 555... if that's what you want to do.

    It would help us to help you if you would describe the problem you are trying to solve. What are you trying to DO? A hundred daisy-chained 555 timers may not be your best solution.
     
  3. AnalogKid

    AnalogKid

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    Jun 10, 2015
    Only to you.

    Is there to be a 0.01 second gap between each of the successive outputs, between the input trigger pulse and only the first output, or what??

    What are the output pulse widths of each of the other 99 555s? If alike, do they have to be *exactly* alike? That will be nearly impossible with 100 separate timer circuits, even with 1% tolerance components.

    IF each of the 99 outputs does not have a 0.01 second gap
    AND IF all of the outputs can be the same pulse width
    THEN look into the CD4017.

    This is a Johnson counter. It has 10 outputs, and as you clock it each output goes high in succession for one clock pulse width. When cascaded, 9 of the outputs are available. So eleven 4017s will produce 99 output pulses without have 100 individual timing circuits. This is WAY less work.

    1 - LMC555 or CD4060 making a 1 s or 1.5 s clock pulse
    11 - CD4017 making 100 output pulses
    Gates used to cascade the counters (see datasheet for circuit)

    What is with the 0.01 second delay before the first output pulse? AND, does the first output occur after the beginning or the end of the input pulse? AND what do the outputs drive? Voltage, current, resistance - anything?

    ak
     
    hevans1944 likes this.
  4. RobertB50

    RobertB50

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    Sep 16, 2016
    Thank you so much for your reply. As each of these timers time out and pulse on, they will check a corresponding sensor for an input. Example: If after the system trigger (starts the 1st timer), a sensor input is returned after .93 seconds, then the PLC can determine it was the 93rd sensor. No need for 93 separate inputs to the PLC (which are expensive).
    I want to keep this simple, since I have to build 2500 of them.
     
  5. RobertB50

    RobertB50

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    Sep 16, 2016
     
  6. RobertB50

    RobertB50

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    Sep 16, 2016
    Since you want to know what I am trying to do, here it is: 2,688 special miniature infrared sensors have been stacked and staggered into a shaft 7 feet long at 1/32 on an inch apart from each other. Even with 32 point PLC input cards, I would need 84 of them to send all those inputs to the PLC. That would cost about $48,000.
    However, if each successive sensor is checked with exactly .01 seconds between each, then one the first sensor is triggered, the PLC will know what the measurement is because of the TIME it took, not because it was the 2,156th sensor.
    Hope this helps.
     
  7. Alec_t

    Alec_t

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    Jul 7, 2015
    Then to be certain of correctly identifying the right sensor would require a timing precision better than 1%. Methinks a chain of 555s won't do it. This project cries out for an MCU scanning a matrix.
     
    davenn likes this.
  8. Bluejets

    Bluejets

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    I'm also wondering how one ir sensor will be able to differenciate from another when physically spaced a little over 30 thousandths of an inch apart.
    For me, that would be the starting point.
     
    davenn likes this.
  9. Bluejets

    Bluejets

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    Oct 5, 2014
    Also wondering if you've given any thought to the possability of using a/d converter.
    Even the little Arduino have 10 bit a/d converters.
    You could use a couple of inputs there to cover your 2000 odd sensors.

    What do you intend to do once you find it is the 2156th sensor?
    If it is solely to display the result, then the above would be realatively easy and accurate.
     
  10. AnalogKid

    AnalogKid

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    How rapidly are you scanning the sensors? Your pseudo-radar approach will work in theory, but not in practice. A timing resolution of 1/10th of 1/2688th of whatever the scanning interval is (at least 26.88 seconds) is not possible with R-C timers. It's not the length of the interval, it's the precision. In round numbers, you need 15 bit timing precision (1/26880, or 0.0037%).

    With a little more logic at each sensor, you can do this without any timers. The string of circuits can be indiviual stages of a looong shif register. Count the clock pulses necessary to get a response back and you have the location. No critical timing depenency.

    In the current system, how many wires are you running along the string, and what are their functions?

    ak
     
    hevans1944 likes this.
  11. hevans1944

    hevans1944 Hop - AC8NS

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    Jun 21, 2012
    It's a start. More information is necessary.

    What is the nature of the "special miniature infrared sensors" and does each produce some sort of analog or digital output that you need to measure or record individually? A datasheet describing the sensor would be helpful.

    Does the seven-foot long shaft rotate? How are the sensors powered, or are they passive devices such as micro-bolometers or FET-buffered pyroelectric sensors that require a voltage (for the FET) before producing an output signal? Are all the sensors active at the same time? Or is power applied to them sequentially via a one-second "trigger" pulse?

    What is the source of the trigger event that starts the measurement ball rolling? How is a sensor triggered (3 V pulse?), and what happens once it is triggered? Is an output produced from a sensor only after it receives a trigger pulse? Are all the outputs somehow paralleled so any of the sensors can produce an output that will be staggered in time after the initial trigger event, but no two or more sensors are producing outputs simultaneously?

    It probably isn't important, but are the sensors spiral staggered around the outer diameter of the shaft or applied in a straight line parallel to the axis of the shaft? How many wires do you think there will be between the sensors on the shaft and "real world" PLC (or whatever) the sensors will communicate with? How will you make these connections? Permanent wiring, i.e., a cable or one or more cables with connectors? As a master electrician, I am sure you have given this some thought. Please share.

    The scheme you are proposing sounds a lot like multiplexing 2,688 sensors on a common output that is "active" for a short period of time for each sensor, as determined by the trigger pulse width applied to any particular sensor. Sequential pulses as suggested by @AnalogKid are easy to generate. How important is it that there be a 10 ms delay between the 1 s "sensor enabling" pulses? Is this to allow each sensor time to disconnect from the common output line before the next sensor is triggered to respond? If each sensor "requires" a one-second time window in which to respond, it will require 2,688 seconds or 44.8 minutes to scan all the sensors. Is that acceptable? It would really be nice if you would tell us what you are trying to DO.

    Hop
     
  12. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    If the sensors have a digital output (on or off) then you can use a fairly simple circuit to read them all at once and transfer them one at a time to a microcontroller (or whatever) then a 74HC165 may be what you're looking for.

    1 chip for each 8 inputs and 3 data lines to your microcontroller. at a reasonable speed (nowhere near the max) you could read all 2000 sensors 500 times per second.

    For 2000 inputs, you would have 250 of these chips daisy-chained. A signal would be sent to read all the inputs at once, and then a second line would be sent a pulse so that the first sensor's reading appears at the output. A second pulse gives you the second sensor's reading, and so on until you've read them all. Then you pulse the strobe input again to read the sensors a second time, sending more clock pulses to read the data. And so it continues.
     
    hevans1944 likes this.
  13. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    My observations:

    EP's brain power is in very good health and still growing. Quite impressive considering all replies thus far have been made without the benefit of OP supplying a single sketch, schematic or photo.

    We need a "Thumbs Up" smiley! ;)

    Chris
     
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  14. AnalogKid

    AnalogKid

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    Jun 10, 2015
    Whether distributed (post #10) or concentrated into 8-stage chips (post #12), I think the shift register approach is far better than 2,688 R-C timers.

    ak
     
    hevans1944 likes this.
  15. hevans1944

    hevans1944 Hop - AC8NS

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    Someone on this forum has ESP (being somewhat older, I forget who...) so maybe they can chime in with a revelation of what the OP is trying to DO. For example, I thought from what I read in post #1:
    that each sensor was triggered on for 1.0 seconds with a delay of .01 seconds between sensor triggers. And
    although a later post said
    are required. So, we have gone from 100 sensors to 2,688 sensors. And even more interesting:
    Is that 2500 sensor assemblies, each consisting of 2,688 "special minature infrared sensors" mounted on 2500 seven-foot shafts, or have you simply reduced the number of sensors on one shaft down to 2500 of them?

    Hop
     
  16. davenn

    davenn Moderator

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    Thread closed

    @RobertB50 PM me with when you have the info asked for and I will reopen the thread

    At the moment you are just causing everyone to wildly guess


    Dave
     
    hevans1944 likes this.
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