IR Detectors

Erikgunit · 2009-12-17 09:29

Hi all. So i am trying to time objects as they pass through a set of IR detectors. Basically i want to keep track of the time it takes from the tripping of the first to the tripping of the last sensor similar to the speed sensors used for bullets and archery. Follow me so far?

So by dividing the distance by time, i will get velocity. cool. I am connecting a the IR emitter from V+ to ground through a 330 resistor and that points to a detector that is connected to V+ through a 20k resistor and is pulled low when the detector detects. it works, at least with one IR pair. And the detector and emitter have to bee within about an inch and i know i should have more distance...

I am using an if then statement to light an led when the beam is broken, and it works pretty well by response time is not that quick and if i move my hand too fast it wont see it. How can i get the precision closer, so that i dont have to worry about speed? If that question makes sense lol. Also I just dont see the IF THen statement to be robust enough to handle three IR pairs. Do i have other options then using IF THEN?

Thanks for your help guys.

Leon · 2009-12-17 12:52

What MCU are you using?

Leon

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Tony B. · 2009-12-17 12:58

I see this is your first post.· For members to be able to help you, you·will need to provide more information about your project, such as, what Micro are you using and your code as an attachment.
I think the goal of your project is understandable.

Erikgunit · 2009-12-17 18:20

The stamp is the BS2.

Im not at my workstation currently so i cant get the code there but ill put what i can remember from last night.

Basically we have a simple If then

Label

IF Right_IR = 0 then unbroken

····· Else High 15 *lights the led telling me that the beam is broken*

····· Debug "Beam is broken."

····· pause 50

····· low 15

Goto Label

:unbroken

Debug "The Beam is unbroken"

goto label

This code works fairly well but when i tried to modify to add more IR pairs i ran into an issue of them not getting a chance to even detect. (If that makes sense.)

I added Elseif statements when i tried to add the other pairs but i think that it was something like this:

Label

IF Right_IR = 0 then unbroken

····· High 15 *lights the led telling me that the beam is broken*

····· Debug "Beam is broken."

····· pause 50

····· low 15

elseif Middle_IR = 0 then unbroken

····· Else High·13 *lights the led telling me that the beam is broken*

····· Debug "Beam is broken."

····· pause 50

····· low 13

ELSEIF·Left_IR = 0 then unbroken

····· Else High 11 *lights the led telling me that the beam is broken*

····· Debug "Beam is broken."

····· pause 50

····· low 11

Goto Label

:unbroken

Debug "The Beam is unbroken"

goto label

It is VERY rudimentary code i know. Thrown together in a few minutes based on what i had seen on line. any optimization and help you guys can give would be awesome.

Leon · 2009-12-17 18:30

The Stamp probably isn't fast enough for what you are trying to do; it's running interpreted code which is very slow.

Leon

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Mike Green · 2009-12-17 20:05

Another piece is that the DEBUG statements take quite a bit of time to execute. They transmit their data whether anything is looking at it or not and, at 9600 Baud, it takes about 1ms per character to do so.

Zoot · 2009-12-17 21:29

Hmmm... certainly the debugs have to go. A Stamp may be fast enough for this if you take a state machine and counter approach, so that the sensors can always be scanned very rapidly and still get other work done, e.g.


Right_IR PIN 0 '  not sure about wiring but it will be easiest if all IR detectors are aligned on nibs
Middle_IR PIN 1
Left_IR PIN 2
More_IR PIN 3
AllIr VAR INA ' or INL if 8 detectors, or INB if pins 4-7 etc.

IrState VAR Byte ' for "capturing" IR input


LedR PIN 12 ' ditto on nib alignment
LedM PIN 13
LedL PIN 14
LedMore PIN 15
Leds VAR OUTD

state VAR Byte
counter VAR Word

time VAR Word ' running total of time to get from first to last detector, in loops

Start:
  LOW Led
  state = 0
  counter = 100 ' set up for "startup" state
  time = 0


Main:

Update_Detectors:
    IrState = AllIr  ' capture current detector status

Update_Leds: 'this could be moved into each state as well, if you want to blink leds at different rates, or whatever
    Leds = IrState' if broken, input is HIGH, so just move values to LEDs


Do_States:
   IF counter > 0 THEN
      counter = counter - 1 ' counter is always decremented to 0 on each pass; states reset to some timeout value
            ' this can be used for delays, led blinks, etc
   ENDIF

   time = time + 1 ' incrementel timer, reset to 0 by state machines
   
   ON state GOTO state0, state1, state2, state3, state4, state5, state6  ' etc
   ' generally ON GOTO and ON GOSUB are much much much faster to execute than IF/THEN/ELSE

   state0: ' the startup state
        IF counter = 0 THEN
           state = 1
           FREQOUT, Speaker, 2000, 2000 ' longer start beep now we're moving!
        ELSEIF counter//20 = 0 THEN ' occasionally make a beep
            FREQOUT, Speaker, 1000, 1000
        ENDIF
      GOTO StatesDone       

   state1:   ' waiting for first beam to be broken
       IF IrState = %0001 THEN ' the first detector (right) must have broken and gone high
          state = 2 ' next state
      ENDIF
      GOTO StatesDone

   state2: ' we don't need to deal with LEDs, so maybe do something useful
              ' here you wait for the detector to go back low again, this state may not be needed if the times are fast 
        IF IrState.BIT0 = 0 THEN ' it's unbroken again
            state = 3
            time = 0  ' reset the time
        ENDIF
         GOTO StatesDone

  state3: ' waiting for middle detector to be broken
        IF IrState.BIT1 = 1 THEN ' it's broken
            state = 4
        ENDIF
         GOTO StatesDone

  state4: ' waiting for last detector to be broken
        IF IrState.BIT2 = 1 THEN ' it's broken
            state = 5
        ENDIF
        GOTO StatesDone


  state5: '  then unbroken
        IF IrState.BIT2 = 0 THEN ' it's unbroken, must be done!
            state = 6
        ENDIF
        GOTO StatesDone
        
  state6: ' done, report the time, a debug here is OK perhaps, if no more objects are coming
       DEBUG CLS
       DEBUG "total time from fully passing through detector 1 ", CR, " to fully passing thru detector 3: ", DEC5 time
       state = 0 ' and do it all again
       counter = 100 


StatesDone:
      ' could do more common stuff here, like printing status to LCD or whatever, nothing to lengthy
      ' more code
      GOTO Main

Now, if you want a little more "time" to show LEDs lit upon a detector change, you could remove the code for updating the LEDs right from the detector inputs, and add a bit of custom code to each state to set LEDs exactly how you want and set the counter to keep them that way for a bit. I will emphasize that using nibbles and bytes for reading inputs and setting outputs is a good way to keep things much shorter (e.g. quicker). The "capturing" of the IR detector pins is so that a change in input pin state in the middle of executing the loop won't throw things off -- ideally such a pin state change would still be "caught" at the top of the loop on the next cycle.

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Erikgunit · 2009-12-18 04:50

Thanks buddy! I cant wait to try it out. Did you just come up with that code off the top of your head? Actually after looking through the code, it looks like everything i ask, on a silver platter. Way more then i could have asked for!!
Another quick question, can the BS2 supply enough current for such a system or would an external supply be better? I am going to assume that it is not but we will see.
well wish me luck, ill be building and testing tonight. Soon!!

Zoot · 2009-12-18 06:24

Well, the proof will be in the pudding. See if it's fast enough to detect your moving objects. Mike may be right that the Stamp isn't fast enough (he often is) -- it really depends on just how fast your objects are moving. Let us know how it works out.

Re: current -- if you are talking about the Stamp's on-board regulator -- it's only good for 50ma or so, if memory serves. Not much. So if you are hooking up a bunch of 5v components you may need an external 5v supply (e.g. a beefier regulator and associated circuitry).

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Erikgunit · 2009-12-18 08:12

well i think i may be trying to power too many LEDs. IR and otherwise. Wheni tryed doing an HIGH outd· nothing happened but a high ledr turned one on.
Does this make sense though. i cant even power 4 leds with a high out put on each LEDs pin. The battery seems ok but i think it may be getting old. getting a new one.
Last question(for the night...er morning,.) the piece of code:

Right_IR PIN 0 '  not sure about wiring but it will be easiest if all IR detectors are aligned on nibs
Middle_IR PIN 1
Left_IR PIN 2
More_IR PIN 3
AllIr VAR INA ' or INL if 8 detectors, or INB if pins 4-7 etc.

Can Allir VAR reference INA. I understand INA is the first 4 inputs but i though VAR had to be bit,nib,byte,word?
That and my IR detectors go low when the beam is broken· but i modded the code to fit. i am just not sure what to do with the LEDs not lighting up, at least all at once...
Thanks for your patience!

Zoot · 2009-12-18 13:24

You can't do a HIGH OUTD -- it's not a "pin" but a variable that refers to the output states of that pin nibble. You set ALL the pins at once:

OUTD = %0001 ' pin 12 high, 13-15 low
OUTD = %1001 ' pin 12, 15 high, 13 & 14 low

etc. Using "OUTX = " only works if the pins are already outputs.

See the Pbasic manual for details about the input, output and dir registers. In my code example I'm just using AllIr as an "alias" to INA -- so I don't have to use INA or IND or whatever in the code. The reason? Makes it more readable AND if you change pins (where LEDs or detectors are hooked up) you don't have to change INA or OUTD or anything in all the places in main program -- just in once place at the top where the variable aliases are defined.

If your detectors go LOW when the beam is broken, that is unusual -- what detectors are you using?

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IR Detectors

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