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LED short distance communications between props — Parallax Forums

LED short distance communications between props

Cluso99Cluso99 Posts: 18,069
edited 2009-11-16 23:24 in Propeller 1
I am going to experiment doing some short (few cms) comms using a single Blue LED at each end. Other colors should work also, although Blue should be less sensitive to external light.

Initially I will use one propeller (protoboard) and 2 cogs, 1 to transmit, one to receive. Then I will get it running in both directions.

Here are some references...

RF ??? short distance comms with the prop & minimum components?·· http://forums.parallax.com/showthread.php?p=851679

LED Touch Sensor·· http://forums.parallax.com/showthread.php?p=589699

Timothy has posted code to do light detection from an LED in the "Led Touch sensor" thread which I might use for a start.

Here is the schematic I am using... P0 and P1 can be any prop pins. Two such circuits will be required. I will face each LED towards each other. It may be necessary to create a pipe between them to eliminate outside light sources??? I have superbright LEDs so will start with resistors around 3K3 and see what results I get.


attachment.php?attachmentid=65139

Please feel free to contribute or experiment along with me cool.gif· It is just a fill-in project at the moment.

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Links to other interesting threads:

· Home of the MultiBladeProps: TriBlade,·RamBlade,·SixBlade, website
· Single Board Computer:·3 Propeller ICs·and a·TriBladeProp board (ZiCog Z80 Emulator)
· Prop Tools under Development or Completed (Index)
· Emulators: CPUs Z80 etc; Micros Altair etc;· Terminals·VT100 etc; (Index) ZiCog (Z80) , MoCog (6809)
· Search the Propeller forums·(uses advanced Google search)
My cruising website is: ·www.bluemagic.biz·· MultiBladeProp is: www.bluemagic.biz/cluso.htm
Led_as_sensor.jpg
633 x 477 - 31K

Comments

  • heaterheater Posts: 3,370
    edited 2009-11-15 08:46
    Does this also work with IR LEDS?

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    For me, the past is not over yet.
  • Cluso99Cluso99 Posts: 18,069
    edited 2009-11-15 09:00
    I think so but not sure.

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    Links to other interesting threads:

    · Home of the MultiBladeProps: TriBlade,·RamBlade,·SixBlade, website
    · Single Board Computer:·3 Propeller ICs·and a·TriBladeProp board (ZiCog Z80 Emulator)
    · Prop Tools under Development or Completed (Index)
    · Emulators: CPUs Z80 etc; Micros Altair etc;· Terminals·VT100 etc; (Index) ZiCog (Z80) , MoCog (6809)
    · Search the Propeller forums·(uses advanced Google search)
    My cruising website is: ·www.bluemagic.biz·· MultiBladeProp is: www.bluemagic.biz/cluso.htm
  • Toby SeckshundToby Seckshund Posts: 2,027
    edited 2009-11-15 10:53
    On a load of AV installs I look at there is always a nagging doubt wether or not the command has,

    1 Happened at all
    2 Got along the wiring and tthen left the led as light

    this leaves you having to carry detectors or using the camera on thr phone, which can be tricky if its a few yards away. One mftr started to use leds that gave out the IR along with visible red. It was a great help when fault finding

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    Style and grace : Nil point
  • Mike HuseltonMike Huselton Posts: 746
    edited 2009-11-15 14:09
    Radio Shack used to sell a business-card sized optical IR detector that up-converted infrared wavelengths to visible wavelengths.
    Very handy, if you don't lose the card. I think it used cadmium sulfide or some such metal salt for conversion.

    Why don't you substitute a piezo buzzer temporarily in-circuit for testing? Leave the resistor in place, as the piezo buzzer has a high impedance,
    at least good enough for testing.

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    JMH

    Post Edited (James Michael Huselton) : 11/15/2009 2:19:57 PM GMT
  • Toby SeckshundToby Seckshund Posts: 2,027
    edited 2009-11-15 14:48
    True, but that leaves you having to change something that might not be faulty. I was just pointing out that, if there is no major performance hit then, visible light suits the sensors either side of my nose, and I try not to loose them. Unless the transfer has to be done by stealth.

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    Style and grace : Nil point
  • Mike HuseltonMike Huselton Posts: 746
    edited 2009-11-15 14:55
    Toby,

    What are you saying?
    Toby Seckshund said...
    I was just pointing out that, if there is no major performance hit then, visible light suits the sensors either side of my nose, and I try not to loose them. Unless the transfer has to be done by stealth.
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    JMH

    Post Edited (James Michael Huselton) : 11/15/2009 3:04:44 PM GMT
  • Mike HuseltonMike Huselton Posts: 746
    edited 2009-11-15 15:09
    I had a thought. Add a visible light LED with resistor in parallel but opposite direction.
    Have the color be distinguishable from the forward LED. Or just use a bi-color LED.

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    JMH
  • Toby SeckshundToby Seckshund Posts: 2,027
    edited 2009-11-15 15:14
    Obviously visible light would attact people's attention. If the equipment is partially hidden so that vandals don't pick on it, the I guess that IR would be better. (Unless the vandals are werewolves, I know that dogs can see IR from remotes)

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    Style and grace : Nil point
  • VIRANDVIRAND Posts: 656
    edited 2009-11-16 04:27
    If low bit rates are OK, the IR remote receiver modules do a good job indoors or with a hood for demodulating
    38Khz IR. Bit rate is probably limited to about 2400 for data, based on how 1-bit sound comes through very awful
    at 9600. Detecting the IR if you can't get one of those Radio Shack cards can use a digital camera's screen.
    You'll need to tinker or use an object to get the IR pulses at 38Khz. If the distance leaves something to be desired,
    you can use more LEDs with a transistor for supplying more current than the propeller pin.
  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 23,514
    edited 2009-11-16 04:31
    I would definitely recommend using a modulated signal. You will not get reliable operation with simple on-off keying.

    -Phil
  • Toby SeckshundToby Seckshund Posts: 2,027
    edited 2009-11-16 08:35
    IF the usual IR RX modules were used then modulation at the required centre frequency is a must. They have very good band pass filters to filter out interference from lighting etc. There are some around that run at 60KHz+ which may allow for higher or more reliable modulation frequencies.

    Judging by Clusso's cct, simple on/off keying is the first experiment. If the data quantity is low, then speed is not an issue.

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    Style and grace : Nil point
  • Cluso99Cluso99 Posts: 18,069
    edited 2009-11-16 09:47
    From research I am expecting only about 250bps, but that is fine for me.

    A pulse of 1mS LED ON is followed by 1mS of Charge, then sampling to determine if the received light was on for 1mS=mark or 0.5mS for space (<=0.7mS is space, >=0.8mS is mark, sampling is done every 100uS). Distance is 3cms and 20degree angle. (missing the link where I found this info)

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    Links to other interesting threads:

    · Home of the MultiBladeProps: TriBlade,·RamBlade,·SixBlade, website
    · Single Board Computer:·3 Propeller ICs·and a·TriBladeProp board (ZiCog Z80 Emulator)
    · Prop Tools under Development or Completed (Index)
    · Emulators: CPUs Z80 etc; Micros Altair etc;· Terminals·VT100 etc; (Index) ZiCog (Z80) , MoCog (6809)
    · Search the Propeller forums·(uses advanced Google search)
    My cruising website is: ·www.bluemagic.biz·· MultiBladeProp is: www.bluemagic.biz/cluso.htm
  • heaterheater Posts: 3,370
    edited 2009-11-16 14:17
    I think I accidentally stumbled on your missing link. The MITSUBISHI ELECTRIC RESEARCH LABORATORIES paper here www.merl.com/publications/TR2003-035/ has all the same numbers.

    They don't use any carrier just on off keying. Seems to work fine for such low data rates and distances.

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    For me, the past is not over yet.
  • mctriviamctrivia Posts: 3,772
    edited 2009-11-16 16:11
    I had an infared remote control that comunicated by pwm. there was a set off time between bits and short on times =0 long on times equaled 1. worked great when coupled with a optical infared filter.

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    24 bit LCD Breakout Board coming soon. $21.99 has backlight driver and touch sensitive decoder.
  • Mike HuseltonMike Huselton Posts: 746
    edited 2009-11-16 22:28
    Cluso,

    What method can I use to Send a parcel 1-3 ounces to you in about a week or less? I have some goodies to send, and this IR topic is one of them.

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    JMH
  • Peter JakackiPeter Jakacki Posts: 10,193
    edited 2009-11-16 22:45
    Ray,

    I don't know if it will help but it's something I used on products over 10 years ago. On the front panel with the normal leds I also had 2 infrared leds which were coupled via transistors back to the CPU's UART. I could use this across the room to upgrade the firmware and read out reports etc. Of course direct sunlight would make it a problem but these things were only ever read indoors anyway. I also did a similar thing with vending machines but the transmitting led could also be modulated to communicate with a portable HP thermal printer that was designed to interface to the IR ports of calculators.

    Anyway, I used one IR led as a receiver in photo-voltaic mode (cathode to ground) coupled directly into the base of an npn transistor whose collector would feed into the receive of the cpu. The transmitter led was fed from a pnp so a low from the cpu's transmit line would turn the led on. Fairly simple stuff but it worked. One version even combined the transmit and receive into one led but still two transistors.

    It also helps if you put these leds down a little tube but makes it a lot more directional.

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    *Peter*
  • Mike HuseltonMike Huselton Posts: 746
    edited 2009-11-16 23:24
    I bought 5 of these transmit/receive ic's and photo detectors www.rentron.com/remote_control/TINY-IR2.htm
    Want a couple?

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    JMH
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