1. Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.
    Dismiss Notice

300MHz RF module

Discussion in 'Electronic Projects Design/Ideas/Reviews' started by bananasiong, Dec 15, 2006.

  1. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

    Joined:
    Nov 17, 2003
    Messages:
    39,331
    Likes:
    653
    Location:
    Derbyshire, UK
    ONLINE
    You don't do Surface Mount then?.
     
  2. audioguru

    audioguru Well-Known Member Most Helpful Member

    Joined:
    Mar 16, 2004
    Messages:
    32,586
    Likes:
    950
    Location:
    Canada, of course!
    ONLINE
    I replaced surface-mount 14 pin ICs without using extra flux.
    I had some defective MP3 players that were "unrepairable" by a store.
    I removed a few good parts from one and swapped the bad parts in another and got one working perfectly.
    The parts were all tiny surface-mount things but I removed and replaced them without using extra flux.
     
  3. Sceadwian

    Sceadwian Banned

    Joined:
    Oct 27, 2006
    Messages:
    14,047
    Likes:
    141
    Location:
    Rochester, US
    You can be sure of one thing auidoguru... =) The joints would be stronger with flux.
     
  4. dave

    Dave New Member

    Joined:
    Jan 12, 1997
    Messages:
    -
    Likes:
    0


     
  5. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

    Joined:
    Nov 17, 2003
    Messages:
    39,331
    Likes:
    653
    Location:
    Derbyshire, UK
    ONLINE

    14 pin ones are hardly anything difficult :D

    My usual ones to change are 80 pin, and fairly small spaced - liquid flux is pretty well essential - although an alternative method is to use solder paste.
     
  6. Hero999

    Hero999 Banned

    Joined:
    Apr 6, 2006
    Messages:
    14,902
    Likes:
    79
    Location:
    England
    You use a SMT inductor, look at the datasheet, it recommends several SMT inductors.

    Again, read the datasheet, it is tuned by programming; this is done by transferring the configureation data into the RAM from a microcontroller.
     
  7. bananasiong

    bananasiong New Member

    Joined:
    Mar 7, 2006
    Messages:
    1,893
    Likes:
    7
    Location:
    Malaysia
    While waiting for the smt parts, I tired to modify the 'crappy' rf module. I'm using a CMOS NAND gate for the transmitter, when I pull up one input of the NAND gate with a 10 k:eek:hm:, it doesn't oscillate as expected. So I turn the transmitter on and off using a transistor by PIC. It works at the bit rate of 10 ms. I'm still learning the method of coding and decoding, this is what I can do so far.
    I wonder why I can't modulate from the logic gate..

    Thanks
     
  8. audioguru

    audioguru Well-Known Member Most Helpful Member

    Joined:
    Mar 16, 2004
    Messages:
    32,586
    Likes:
    950
    Location:
    Canada, of course!
    ONLINE
    Do the Cmos gated oscillator like this:
     

    Attached Files:

  9. bananasiong

    bananasiong New Member

    Joined:
    Mar 7, 2006
    Messages:
    1,893
    Likes:
    7
    Location:
    Malaysia
    Any NPN transistor will do right? I'll use 2N3904 for this. If I do it this way, can the bit rate be faster? But I don't know whether the poor receiver can receive as fast as the transmitter do or not.

    Thanks
     
  10. audioguru

    audioguru Well-Known Member Most Helpful Member

    Joined:
    Mar 16, 2004
    Messages:
    32,586
    Likes:
    950
    Location:
    Canada, of course!
    ONLINE
    I think the LM567 in the receiver is slow. Its max switching speed is f0/20. f0 is about 7kHz so the switching speed is 350Hz.
     
  11. bananasiong

    bananasiong New Member

    Joined:
    Mar 7, 2006
    Messages:
    1,893
    Likes:
    7
    Location:
    Malaysia
    So the fastest switching time is 2.85 ms per bit right?
     
  12. audioguru

    audioguru Well-Known Member Most Helpful Member

    Joined:
    Mar 16, 2004
    Messages:
    32,586
    Likes:
    950
    Location:
    Canada, of course!
    ONLINE
    Yes but only when the PLL is tuned exactly to the modulating frequency. If it is not exactly the same then it needs additional time to lock to the modulating frequency.

    The super-regen receiver has some capacitors that attenuate its squegging oscillation that might also slow things down.
    I think the receiver is designed to slowly switch a relay on and off.
    CHEAP, CHEAP, CHEAP, CHEAP stuff works poorly.
     
  13. mramos1

    mramos1 Active Member

    Joined:
    Sep 15, 2005
    Messages:
    2,403
    Likes:
    9
    Location:
    Boynton Beach, Florida USA
    How small could something like this be made and how low could the power be reduced to? Like 1.5 or 3 volts, maybe pulse it?

    Hero999 you input is welcome as well. I have a need for this as well. Not trying to hijack the thread.
     
  14. audioguru

    audioguru Well-Known Member Most Helpful Member

    Joined:
    Mar 16, 2004
    Messages:
    32,586
    Likes:
    950
    Location:
    Canada, of course!
    ONLINE
    The transmitting transistor would transmit very low RF power with a low supply voltage. So its range will be small.
    An ordinary Cmos gate has a minimum supply of 3V but its output current is very low. A 3V battery's voltage drops to 2V over its life. A 74HCxx Cmos gate has a minimum supply voltage of 2V and has a higher output current.

    What good is a transmitter that is not turned on? Hardly ever used like a car door remote entry?
     
  15. bananasiong

    bananasiong New Member

    Joined:
    Mar 7, 2006
    Messages:
    1,893
    Likes:
    7
    Location:
    Malaysia
    What is a flux residue? Need to clean it up after using the liquid flux?

    How do I calculate the frequency of the Cmos oscillator?
    Why I can't do it like mentioned previously, just add a pull up resistor. From your schematic, the transistor also acts as a switch right?

    Thanks
     
  16. Sceadwian

    Sceadwian Banned

    Joined:
    Oct 27, 2006
    Messages:
    14,047
    Likes:
    141
    Location:
    Rochester, US
    The flux basically 'floats' to the top of the soldering joint once the solder hits it and leave a residue over the top of the joint, some types of flux leave a corrosive residue which needs to be cleaned off afterwards. Depends on the flux.
     
  17. audioguru

    audioguru Well-Known Member Most Helpful Member

    Joined:
    Mar 16, 2004
    Messages:
    32,586
    Likes:
    950
    Location:
    Canada, of course!
    ONLINE
    The Cmos oscillator turns on the transmitter and turns it off. Then the modulation is digital AM.
    The calculation for a classic Cmos oscillator is here:
     

    Attached Files:

  18. bananasiong

    bananasiong New Member

    Joined:
    Mar 7, 2006
    Messages:
    1,893
    Likes:
    7
    Location:
    Malaysia
    Where are the values from? 0.559 and 0.455.
     
  19. audioguru

    audioguru Well-Known Member Most Helpful Member

    Joined:
    Mar 16, 2004
    Messages:
    32,586
    Likes:
    950
    Location:
    Canada, of course!
    ONLINE
    MM is an IC prefix used by National Semiconductor so it might have been on their applications note. The same formula is in my "Cmos Cookbook" written by Don Lancaster.
     
  20. bananasiong

    bananasiong New Member

    Joined:
    Mar 7, 2006
    Messages:
    1,893
    Likes:
    7
    Location:
    Malaysia
    From the attachment, it says that if the supply is higher, the higher it can oscillate, means frequency?

    The receiver is really po_Or
    After it is tuned well, the next day or after it has been turned off for a while, I need to re-tune it, or else I cannot get the signal transmitted. And sometimes, no matter how I tune it, it just wouldn't work. Then it worked the next day -_-"
    Now it is not working, maybe I'll try it tomorrow.. :(

    Thanks
     
  21. audioguru

    audioguru Well-Known Member Most Helpful Member

    Joined:
    Mar 16, 2004
    Messages:
    32,586
    Likes:
    950
    Location:
    Canada, of course!
    ONLINE
    A Cmos inverter or gate has a higher output current with a higher supply voltage so it can switch faster. I use a two-inverters Cmos oscillator at 1.6MHz on a 12V supply and it works well.

    I think your receiver is crappy. Cheap, cheap cheap!
     

Share This Page