Many electronics and robotics applications require localization, that is it needs to know where it is. In this article I will go through a localization method I invented that works with all RF modules.

My method of RF localization is not very accurate nor is it precise. It does not give you exact coordinates nor does it work well indoors. However, what it does do is provide you with the approximate distance to an object outdoors. Better yet, my method for RF localization works with EVERY RF module that can transmit serial data.

First, you will need a transmitter module and a receiver module. To demonstrate how this method works for any RF module, I will use the cheapest RF modules I can find.Using those Transmitter and Receiver modules I got around +- 15 feet precision localization.

This transmitter - http://www.sparkfun.com/commerce/product_info.php?products_id=8946

This receiver - http://www.sparkfun.com/commerce/product_info.php?products_id=8949

My method of RF localization is based on the principle that the more power a RF transmitter has, the farther the RF signal goes.

The transmitter sends out a different encoded RF signal at varying power levels. At each different power level, the transmitter sends a different byte. Therefore depending on which signals are received, a receiver would be able to approximate its distance from the transmitter.

So after a test we would have a chart similar to this generated:

Note: Bytes were encoded using an encoding method and the minimum power for the transmitter is 2 volts , and maximum is 12 volts)

Power Level Byte Distance
2 volts 0x02 3 feet
4 volts 0x04 6 feet
6 volts 0x06 25 feet
8 volts 0x08 60 feet
10 volts 0x10 90 feet
12 volts 0x12 125 feet

We see an obvious ( but not really linear) relationship between power level and distance.

The transmitter sets the power level and then sends the respective byte. It repeats for all bytes and all voltages.The receiver merely has to check which bytes it received and based on which bytes it received it can estimate distance.

The transmitter uses diodes ( with a 2V drop) and transistors. The diodes' voltage drops are a crude way of generating different voltage. The transistors switch the different voltages to the transmitter's power pin.

Transmitter Schematic:

Here is a sample receiver schematic ( could really be anything with a receiver in it)