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I have been running a simple RF link between 2 arduini uno recently and everything went faily well. I am now trying a new project with an arduino mini pro (5V/16MHz) and the seeeduino RF link (@315MHz), and I see very odd results : when the transmitter is on USB cable, the link runs ok, but when on a 9V battery (as raw voltage input), I get very very limiter range (a few inches).

Because the setup works on USB, I'm assuming that the current limitation on the GPIO that powers the RF transmitter is not the issue here. It therefore has to be the battery itself or the regulator.

Somehow I need to use a GPIO to shut down the radio during power saving phases. My current design is very basic, I should probably add a transistor to enable power on the RF. I was also thinking maybe the RD oscilliator needs to settle down a bit, I may need to add some delays before starting to send data. I can see on the oscilloscope that the data and power PINs seem to behave correctly, although I have noticed a voltage drop on the power pin which is similar in pattern to the data transmitted (but again this is no issue unless using the 9V battery).

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  • 9V batteries can't provide that much current. You should measure the current consumption of the RF module. You could try adding a electrolytic capacitor, parallel to the battery. You could also power the RF module directly from 9v, to increase the range (higher voltage; better range). But I'd just use a battery pack, instead of a 9v battery.
    – Gerben
    Dec 14 '15 at 16:16
  • You should never power anything from an GPIO pin except incredibly low powered things (<20mA), and an RF transmitter certainly does not fit into that category. Google "High Side Switch MOSFET" for a circuit that can help you
    – Majenko
    Dec 14 '15 at 17:19
  • Thanks all, I appreciate that I need to use a power switch in a proper design, maybe then I can use the 9V directly. I'll be looking out for these high side switch.
    – takumar
    Dec 15 '15 at 8:48
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As established in the comments, the issues here are powering the module directly from a GPIO pin, which are limited to 20 mA, and potentially the limited current of a 9V battery.

Personally I avoid using 9V batteries in projects, as they are comparatively expensive for the lifetime they provide. There are various boost/step-up converters that make a steady 5V supply from two AA batteries.

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