manchester coding

james andrews · Guest

hi,
ive seen lots of information saying that manchester coding is good as it provides a zero dc component. i know what manchester coding is, but why is the zero dc component important in radio transmission?
i was thinking of wasy of making two pics talk to each other and was wondering if this was a good way to go.
thanks
james

AllanL5 · Joined: 05 Apr 2004 Posts: 6

In Radio transmission, you CAN'T transmit a DC component -- you can only transmit AC signals. Also, when you capacitively couple signal stages, any DC component will be lost. This will result in a distorted data signal. Manchester encoding gets around all this.

Another way around it is to have a 'HIGH' signal produce one tone, and a LOW signal produce another tone. The tones have no DC component either, so get around the DC component limitation. This is how modems work on telephone circuits.

The easiest way to get two PIC's to talk to each other is through some RS232 port use. Signal at 0 to 5 volts, and you won't even need a MAX232 driver chip.

For distance (300 feet) you can use the MAX232. For longer distance (4000 feet) you can use RS485 drivers.