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IR Beacon — Parallax Forums

IR Beacon

vla7vla7 Posts: 79
edited 2008-11-16 14:18 in Robotics
I built my own IR beacon using a 555CN Timer IC· from Radio Shack.· I followed the instructions on "IR Remote for the Boe Bot" in appendix C.· So far I've been powering it with Vdd from the Boe-Bot which I believe is regulated 5 volts.· The package for the 555CN Timer states the the supply voltage is 4.5 - 16V.· If I power my beacon with a 9 volt battery, can I still follow the schematic from appendix C or will I have to calculate new resistor values?

Comments

  • noobmunchernoobmuncher Posts: 124
    edited 2008-11-15 07:10
    In my tests, I have never had to change the resistance, with that said though i am not quite sure I understand how your circuit is set up.
  • ercoerco Posts: 20,256
    edited 2008-11-15 11:54
    Do you mean that your circuit·delivered a reliable·38 kHz signal using fixed resistors and caps? If so, consider yourself lucky. I always count on needing a 10K pot to·center the frequency for maximum range.

    The frequencies of the 556-based beacons I've built·are surprisingly insensitive to voltage changes, so I suspect your 555CN will operate about the same on 9 volts as 5.·Hopefully this is true for you, because you'll discover that 9 volt batteries don't last very long in continuous use, they'll be down to 7 or 8 volts before you know it. For a stationary beacon, you'll want to use a wall-wart AC adapter for power.

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    ·"If you build it, they will come."
  • GWJaxGWJax Posts: 267
    edited 2008-11-15 13:15
    Like erco said the 555CN timmer chip is very stable when changing voltage, the output will stay the same but if is a stationary beacon replace the bettery with the wall-wart if this is feasable or use rechargeable D' to sustan the current longer. Plus I too am impressed if you got that fixed 38kHZ without a VR!! You must have used millitary 1% tollarance resistors and found a few dead on.. Or you changed your program to pick up a diffrent frequency based on you beacon.

    Jax

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    If a robot has a screw then it must be romoved and hacked into..
  • Lab RatLab Rat Posts: 289
    edited 2008-11-15 14:13
    i lovw that signature must be hacked into i go shoping for robot toys for this reasonlol

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    Parallax posesses power beyond belief.

    Believe in it.
  • vla7vla7 Posts: 79
    edited 2008-11-15 15:55
    Sorry, I guess my question is a·bit confusing.· I built the circuit using a 10kohm pot which·I regulate to get the right frequency.· I'll plan·on replacing this·with resistors eventually.· My·question about·recalculating the resistance thought is·regarding the infrared LED.· There is a 220 ohm resistor connected the LED but I assume that this was calculated based on a 5 volt output.· So if I put a 9 volt will I have to recalculate the resistor based on 9 volts or does the timer itself have a voltage regulator.· Pin 7 of the timer is also connected to a 470 ohm resistor going to Vdd, will this have to be changed also?· See my attachment for the schematic.
    ir question.jpg
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  • ercoerco Posts: 20,256
    edited 2008-11-15 17:40
    As long as you NEVER EVER·nono.gif· hook your 9V-powered beacon to your Stamp (which would damage the Stamp) you should be OK without changing resistors. The 220 ohm resistor is both an LED current limiter and protection to the stamp input pin. The LED will get the 555's 50% duty cycle output, which at 9 volts will effectively cut the 32 mA steady-state LED current down to ~16 mA.· Various IR LEDs range from 20-100 mA max continuous current. Check your 555CN's output current specs to make sure it can keep up. smhair.gif

    Function-wise, that 220 ohm resistor can be reduced or increased to change the beacon's output level. A single LED has a very narrow beam width (like +/- 15 degrees) so you may want to use multiple LEDs (each with its own series resistor) if you are using it for navigation. See an example of one of mine at http://www.botmag.com/articles/scribbler.shtml· . Too strong a signal will reflect off different items and your robot may track toward a ghost reflection. Better to use several moderate-strength LEDs fanned out in different directions than one giant one.

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    ·"If you build it, they will come."
  • vla7vla7 Posts: 79
    edited 2008-11-15 18:54
    Is it necessary to use a voltage regulator for the beacon?
  • GWJaxGWJax Posts: 267
    edited 2008-11-15 20:37
    No you don't need to regulate your voltage for the beacon, the 555CN can handle the diffrence in voltage just fine, though I would use a wall-wart for this to keep it as smooth as possible without adding and more electronics but adding a few caps never hurts to keep the voltage ripple down from these.

    Jax

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    If a robot has a screw then it must be romoved and hacked into..
  • vla7vla7 Posts: 79
    edited 2008-11-16 00:01
    ok, I just want to confirm I'm understanding this.· If I build the attached circuit on the boe-bot and tune my pot so that I'm sending a 38khz signal and then power the circuit from a 9 volt battery instead of the bo-bot, it will still continue to send the same 38khz signal and I won't have to retune the pot or change any of the resistance?
    IRbeacon.JPG
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  • Mike GreenMike Green Posts: 23,101
    edited 2008-11-16 00:33
    The circuit you've shown is supposed to be stable with respect to the operating frequency over the full supply voltage range of the 555.

    The IR LED will probably have problems with the current through the 220 Ohm resistor with a 9V supply voltage. You should switch to a 470 Ohm resistor to keep the current under 20mA. Some LEDs can handle more current. Check the datasheet for the LED.
  • ercoerco Posts: 20,256
    edited 2008-11-16 04:29
    vla7 et al:

    Just curious about the 555 circuit shown. I'm familiar with the Scribbler's IR abilities, less so the BoeBot. If the Scribbler sees a steady 38 kHz beacon (such as the 555 emits), it only detects it momentarily, because its IR sensor expects a modulated carrier and its internal filter circuitry is not "continuous signal acceptable". That's why I had to use a 556 circuit instead of a 555. Is the IR detector in the BoeBot continuous signal acceptable?

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    ·"If you build it, they will come."
  • Mike GreenMike Green Posts: 23,101
    edited 2008-11-16 05:18
    erco,
    It depends on the IR detector. The Panasonic one accepts a continuous 38KHz signal as far as I know. There's another one that Parallax sells and uses that does not.
  • vla7vla7 Posts: 79
    edited 2008-11-16 06:42
    Thanks everyone, I succesfully built my first IR beacon! cool.gif
  • GWJaxGWJax Posts: 267
    edited 2008-11-16 14:17
    The Sharp IR dectector also accepts a continous 38Khz signal as well and is used in alot of the older VCR's and the newer TV uses mostly the Panasonic dectectors at least the one that I have removed during parts rip down.

    Jax
    Mike Green said...
    erco,
    It depends on the IR detector. The Panasonic one accepts a continuous 38KHz signal as far as I know. There's another one that Parallax sells and uses that does not.
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    If a robot has a screw then it must be romoved and hacked into..
  • GWJaxGWJax Posts: 267
    edited 2008-11-16 14:18
    Congrats vla7!!!jumpin.gif

    Jax
    vla7 said...

    Thanks everyone, I succesfully built my first IR beacon! cool.gif



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    If a robot has a screw then it must be romoved and hacked into..
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