I'm currently working on a project involving Wifi transmission. The device needs to send a 1-3 digit number to a computer/phone that is 5-15 feet away. Approximately how much energy will this take to send one number?

Thank you!

Austin

 

It would be very small (likely less than a mw), depending upon the antennas used.

 

What is the power output of your WiFi transmitter? A better question is what current does it draw when transmitting? How much current does it take when not transmitting? Are you going to turn it off when not needed, then reinitialize it... Along with negotiating a new connection? Will it do this more than once on some periodic basis?

I would imagine the energy to send one number is a fraction of the total energy budget here.

 

Since you asked for a rough figure, I have made some rough calculations. Here they are:

You're sending a number of maximum 3 digits. So thats about 10 bits minimum, if all the digits have equal probability of being sent. (0 to 999).
Your target is at a maximum distance of 4.5 m. Depending on the sensitivity of your receiver, the transmit power you require may vary. I am doing this calculation assuming a receiver of sensitivity -90 dBm. That is \(\small{10^{-12}}\) Watts of power needed at receiver. Based on the free space path loss model, and assuming you're using WiFi in the 2.4 GHz band, the transmit power required is around \( \small 2.1357 \times 10^{-07} \) Watts or, as many Joules per second. Now, the energy you require depends on your bit rate. Assuming that you use the maximum raw data rate of WiFi (IEEE 802.11b), that is 11 Mbit/s, the energy you need to transmit 3 bits is \( \frac{3 \times 2.1357 \times 10^{-07}}{11 \times 10^6} \) which is \( \small 5.8246 \times 10^{-14} \) Joules, or around 0.06 picoJoules. Which is very, very, small. I hope I haven't made any silly mistakes here.

And, as ErnieM pointed out, this would only be a fraction of the energy you will actually use, since the system will usually have many, many losses.