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Changing Rx from 12V with relay to 4.5V no relay

Discussion in 'Wireless & RF Design' started by phildupuis, Dec 9, 2009.

  1. phildupuis

    Thread Starter New Member

    Dec 9, 2009
    I'm really new at this so I may not know all the terms at this point.

    Please have patience as I'm learning.
    I purchased a Tx and Rx from ebay that was just a plug and go(came with relays, chip all pre-assembled ready to go), cool... works great! But Rx needs 12V to operate a relay. It drained my batteries.

    -I only wanted to control a small 3V motor (on or off), relay not needed.
    -Wanted it silent, the relay clicked pretty loud - took it out
    -wanted to go down to a lower voltage circuit (3x AAA batteries)
    So I purchased another Tx and Rx from ebay

    • Distance: 100M(330 feet)
    • Type: RF radio
    • Carrier freq. 315MHz
    • Max data rate: 10KHz
    • Power supply: 5V~6V
    • Encoder/Decoder: No
    • Output type: Square wave
    • Size: 20mmx 18mm x 5mm (Tx)
    • Size: 30mm x 20mm x 5mm (Rx)
    I hacked it into the circuit of the other one (because I wrecked the Tx and Rx of the other unit while playing around)

    The transmitter is still using a 12V "23A" alkaline battery from initial unit.

    See attached picture of the circuit for the Rx that I put together.

    It works if I'm really close (2 - 3 feet). Can't get much range.

    The unit used to work at almost a block away in the original state. Is this because I downsized the voltage of the Rx from 12V to 4.5V??

    What can I do to increase the range.

    If I put my multimeter between Ground and the lead before the 3.3K Resistor, I get a reading of 3.8V, if I walk away farther then 3 feet, the current drops down to 0.48V, so the motor sputters.

    Any Ideas? Thank you so much for your help.