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Say you need a wireless communication channel to a single device with a range of 1 meter, and a date rate of 10 b/s. What you are after is to minimize the power consumption whilst keeping the antenna small (5x5 cm). What would be the best approach for this?

I'm thinking you need to avoid PLLs etc. because they are just too power hungry. You can generate a single frequency with an oscillator, add some switches and you have a transmitter. I am not too sure about the receiver though.

Or can you use some sort of coupling in this short range? Something similar to wireless charging but for comms.

I have one of those bicycle computers that measure the speed you are going and they seem to last forever. I've done 1000 km and it is still going on its original coin battery. How do they do it?

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  • \$\begingroup\$ The bicycle computers have a really low power profile. An MCU spending 99% of its time in low-power sleep, waking up on interrupts from the sensor and driving a no-backlight LCD which takes almost no power. Transmitting and receiving data is a whole other kettle of fish. \$\endgroup\$ – DoxyLover Sep 12 '16 at 22:57
  • \$\begingroup\$ The bicycle computer is wireless though. The magnet is separated from the display. \$\endgroup\$ – user110971 Sep 12 '16 at 22:59
  • \$\begingroup\$ rfid can be very low power (the "tag" can get all its power from the transmitter), and they can work over 1m. The transmitter still needs a fair amount of power though. Have you looked at what your bicycle computer is using? \$\endgroup\$ – Andrew Spott Sep 12 '16 at 23:07
  • \$\begingroup\$ No, I haven't. The setup is a magnet attached to the wheel; a reader that passes close to the magnet and is attached to the frame; the display bit on the handles. It can also wake up without you needing to press any buttons, so it detects when you start moving. \$\endgroup\$ – user110971 Sep 12 '16 at 23:11
  • \$\begingroup\$ The "reader" of your bicycle computer is probably just a reed sensor, a mechanical switch that close when exposed to a magnetic field. It requires no power at all when the magnet is away, yet can send a pulse to the computer to wake it as soon as you start riding. \$\endgroup\$ – Sylvain Sep 20 '16 at 19:06
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I think a narrow Pulse of IR is probably the lowest average current for transmitting 1 rev with the path loss fixed. PW depends on sensitivity of Rx.

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