Momentarily boost 5V to 9-12V for RF transmission

Discussion in 'General Electronics Chat' started by Tuppe, Nov 19, 2013.

  1. Tuppe

    Thread Starter New Member

    Dec 30, 2011
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    Hello!
    I'm building a RF(434Mhz) based temperature station, in which I have multiple transmitters around my house sending temperatures, every 5-10 seconds.
    I most likely power them off the wall socket.

    I'm able to get some decent range with MCUs 5v supply, but I'd like to extend the range up to the 12v that the transmitter allows.
    Could I use 5v to 12v boost converter to momentarily boost the voltage when I send the data? Meanwhile it would refill the caps until the next sending. Would there be any sense doing so?

    I'm also trying to make it cost efficent, max. 10$ per transmitter.

    I'd be able to change the supply voltage to 9-12v, but that would require step-down for the MCU. I'd still like to have some room for 5V battery power option.

    Bonus question:
    Would there be any sense to power the RF module through Atmega output pins? In this way I'd be able to send power to the module only when I'm transmitting. So that if I accompany a boost converter, it wouldn't be hogging current all the time.
     
    Last edited: Nov 19, 2013
  2. #12

    Expert

    Nov 30, 2010
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    A CMOS version of the 555 timer can be used as an oscillator at 5 volts Vcc. Then rectify the output with a voltage doubler configuration for about 8 volts. Ride that on top of the 5V rail with a coupling capacitor (before rectifying) for about 12V.

    Running at a few kilohertz will allow keeping the current cost and capacitor sizes really low.
     
  3. Tuppe

    Thread Starter New Member

    Dec 30, 2011
    5
    0
    Sounds like interesting idea, I was able to get 9v out, neat!
    I didn't quite understand that one... I'm still a novice in electronics. Do you mean voltage tripler circuit, or is there simpler way?
    [​IMG]

    How does that method compare to using modules like this:
    http://www.ebay.com/itm/271196268868
    These use MC34063(https://www.sparkfun.com/datasheets/IC/MC34063A.pdf)
    which seem to have similar characterstics to 555 timer circuit, but only with dedicated purpose for DC-DC boosting.

    I'd like to have the projects as simple, small size and cost efficent as possible. As for now, I only have Attiny85, DHT22 sensor and RF transmitter on 3cm x 3cm perfboard.

    Thanks!
     
  4. #12

    Expert

    Nov 30, 2010
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    This is what I was thinking. Now...to see if it works...

    (I'm only firing on 3 cylinders right now because I had surgery 4 days ago. Try to expect a bit less quality from me this week.)
     
    Last edited: Nov 19, 2013
  5. Tuppe

    Thread Starter New Member

    Dec 30, 2011
    5
    0
    I wasn't able to get that working, I must've misunderstood something.
    This is what I have running now:
    [​IMG]
    There's 10uF decoupling capacitor, so replacing that with 22.1uF is what it did, but seems like I still don't get it.

    What you think about the eBay module though? Is it the same as this 555 timer solution?

    I'm sorry to hear that, I hope you get well!
     
  6. #12

    Expert

    Nov 30, 2010
    16,346
    6,835
    I'm not sick, just can't seem to get up to normal speed this week. (Getting old sucks.)
    I actually believe the voltage doubler riding on the 5 volt supply should work, but I don't know if I'm wrong. I wish somebody smart would examine my circuit and give an opinion.

    Those eBay modules use an inductor circuit to kick the voltage up, not a simple oscillator with rectifiers. Bottom line: Use anything that works. I'm trying to find some tiny, 1 watt boost modules, but they have disappeared into the partition I call, "electronics".

    Help, guys. I'm not getting this one right.
     
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