Shop OBEX P1 Docs P2 Docs Learn Events
wireless audio--stumbled upon by accident, how to improve? — Parallax Forums

wireless audio--stumbled upon by accident, how to improve?

P!-RoP!-Ro Posts: 1,189
edited 2010-11-07 05:12 in Accessories
Originally trying to transmit audio by light, I noticed a strange occurrence if I tried increasing the volume further with an lm386. The audio would get really loud if the photoresistor wasn't viewable by light. I changed the board and power supply to ensure there wasn't any inductance and I found out the sound was rf...

Just playing around not knowing what I'm doing I can get fuzzy sound off of the singing seven demo, but that isn't good enough. I'm hoping to learn more about rf so I can create a stronger signal and stronger reception. Anyone here know enough about rf to help? I was hoping to use this idea on my robot...

BTW--the schematic is simple. The prop pin is attached to multiple long wires, and on the reception end I have long wires attached to a lm386 with the standard setup to speakers.

Comments

  • kwinnkwinn Posts: 8,697
    edited 2010-10-24 20:57
    A little more info regarding the software would be helpful. If you were using PWM to generate the light/audio you could be picking up one of the PWM signal harmonics. When I was a servicing minis a couple of high school students used a basic program on the computer to play music on a nearby radio. Fuzzy music like you were getting, but music never the less.
  • P!-RoP!-Ro Posts: 1,189
    edited 2010-10-24 21:48
    Just the standard programs for the prop, and yes they use pwm. Talking to my grandpa I improved my transmit circuit so a cap goes to the base, ground to the emitter, 10k from 5v to collector and 100k from 5v to base. A cap goes from collector to the antenna. Currently, I'm working on improving my detector part.
  • kwinnkwinn Posts: 8,697
    edited 2010-10-27 09:07
    You might try placing an AM radio near the prop and tune it over the entire band to see where the reception is best. You could probably use the prop as a short range AM transmitter by using a pin to produce RF (square wave) and a second pin for PWM audio to modulate the RF signal. Be careful not to break FCC regs.
  • P!-RoP!-Ro Posts: 1,189
    edited 2010-10-27 14:25
    Break fcc regs? No worries, I'm still a minor ;)
  • P!-RoP!-Ro Posts: 1,189
    edited 2010-10-27 22:06
    And after some mods I've run into a new stinkin' problem...It's picking up radio stations. At least it has no static (other than random, light ringing that seems to happen every 2 seconds or so). I'll talk to my grandpa about it another day.
  • ercoerco Posts: 20,255
    edited 2010-10-31 15:03
    Are you using a CdS photoresistor as your receiver sensor? Those have a fairly slow response time compared to phototransistors, FYI. Even a solar cell is better than a CdS photoresistor.
  • kwinnkwinn Posts: 8,697
    edited 2010-11-01 07:23
    Pick up of radio stations is probably due to not having any tuning circuit to select a specific frequency. Any RF signal will be demodulated and amplified.
  • Peter KG6LSEPeter KG6LSE Posts: 1,383
    edited 2010-11-01 11:39
    Iam with Erco .I use a Solar cell as a uber large photodiode .

    It works Very well

    """Break fcc regs? No worries, I'm still a minor ""

    If the FCC sees you in to techy stuff like this the will expect you to know what you are doing .

    a 4 YO can get a ham license . there held responsible..


    BTW I am a Part Of the Civil Air Patrol as a Comm and IT specialist. we do S/R for ELTs ( SOS beacons ) there on 121.5 ( old ) and 406 (New) MHz .

    First week I was involved we responded to a ELT and it set off one of the U.S. Air force ELT satellites . we responded and spent over 10 man hours Flying and driveing finding what to the US GOV was a destrees signal ! .
    we found the Sig and it was a Belkin Ipod Dock in a kids room .

    these missions costs the Gov Lots of $$ . and if its intentional there is severe civil and legal penlitys in place ..regardless of age . you parents are responsible too .

    Hams also do T Hunt for anything jamming there fun too .

    not to alarm you . but please use a receiver Or Spectrum analyzer like I do and make sure nothing you make puts any kind of Sig on 121.5 or the ham bands .

    I do a TON of RF tinkering . Its What I do as a ham and a geek .

    May I recommend a ARRL handbook , there not Just for hams . there a MUST read for any electronics tinkerer or professional alike . I have mine as a CD too . there a great resource .

    RF is a Very black magic kind of thing at times . its easy to understand after that book .
  • P!-RoP!-Ro Posts: 1,189
    edited 2010-11-01 16:14
    IDK how to get the mhz reading so...
  • kwinnkwinn Posts: 8,697
    edited 2010-11-04 06:02
    You are delving in to an area where you need a fair bit of background knowledge to understand what is going on. I would suggest looking into getting a ham license or taking a basic electronics course. Or both.
  • P!-RoP!-Ro Posts: 1,189
    edited 2010-11-06 21:38
    Nah, I know enough about basic electronics. I just need to find out more in the higher specialized fields. I wish I had more time to be working on that right now, but enough of it is spent working on creating a mini mendel (huxley) instead.
  • Peter KG6LSEPeter KG6LSE Posts: 1,383
    edited 2010-11-07 05:12
    P!-Ro wrote: »
    Nah, I know enough about basic electronics. I just need to find out more in the higher specialized fields. .



    the ARRL book is not a easy nor a hard book . its DC to daylight in more ways then one . it will get you from where ever you are to where you need to go .
Sign In or Register to comment.