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I want to do wireless communication between ATmega32 and Arduino Leonardo. I used RF433 MHz transmitter and receiver as shown in figure.enter image description here

I used USART at baud rate 300 at transmitter and receiver, but communication is not happening.What may be the problem.

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    \$\begingroup\$ You are transmitting a single wire serial signal as USART (synchronous) ? \$\endgroup\$ – Cornelius May 15 '14 at 18:03
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    \$\begingroup\$ If it is synchronous, where is the clock? \$\endgroup\$ – Cornelius May 15 '14 at 18:06
  • \$\begingroup\$ If i connect microcontroller to a computer, do we use clock. \$\endgroup\$ – Harish_N May 15 '14 at 18:07
  • \$\begingroup\$ Can you check with an oscilloscope the signal at receiver? \$\endgroup\$ – Cornelius May 15 '14 at 18:09
  • \$\begingroup\$ It is a serial communication at baud rate of 300. Instead of RS232 cable i'am using wireless transmitter and receiver. \$\endgroup\$ – Harish_N May 15 '14 at 18:10
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Almost certainly (unless you are using RF modules with in-built MCUs) you haven't read the data sheet on the radio modules and if you had you'd have realized you cannot expect to connect a uart at either end and expect this to work as if it were linking two PCs with an RS232 cable. Look at this: -

enter image description here

When not transmitting data the output from the receiver will be gobbledy-gook and nonsense. Look at left of diagram. When the transmitter starts sending data, it has to "attract" the receiver circuits to lock-in to the transmission - this is what the preamble does and, after a few milli seconds sensible preamble data is received from the receiver and, the micro controlling the uart will know to pretty soon expect the first sensible byte of the payload transmission.

The picture above was drawn with FM modulation in mind but it's pretty much what happens on AM too.

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  • \$\begingroup\$ +1 on this answer. Also long sequences of 1 or 0 will cause the demodulator to loose sync. It might work usually, but a 0xFF or 0x00 will not decode reliably. \$\endgroup\$ – Bryce May 6 '15 at 22:51

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