steviemidnight
Junior Member level 1
my 433MHz walkie-talkie project summary:
re RF project thread: **broken link removed**
after reading/researching and your help i know the following.
I need a anti-alising filter after the mic to prevent spectral repetitons. i have decided to go for a 5 or 7 order chebyshev with a .5 db ribble. this has a good steep curve which cuts of frequencies below 4Khz which sould stop all anti-alising.
I can get pics with an on board ADCs and UARTs, the 16C74 has a 8 bit A/D and a UART. ok i need a speech codec before the Tx this can be built using the 16C74 and its A/D then writting a few lines of code to encode the bit stream with stop, sync and parity bits depending on my chosen method of encription.
I then need to decode this at the RX end. the Rx will let in a lot of unwanted interference/noise and so the reciver code will be more complicated, as i believe. i need to decode the sent packets of information with some kind of error checking. A warm up signal from the Tx encoder would help be set up the Rx decoder - but unsure
Ok manchester code is 50% efficent has it encodes a 1 with a 1 then the opposite a 0, which doubles the length of the bit stream. i have available data rates of upto 128kbits which should be enough.
The RS232 standard is intended for relatively short (50feet or less), relatively low speeds(19kbit/s) serial communication over a wire. this could work as it is implimented in radio modems, but is not designed for this purpose and so would cause problems.
GSM speech codec use only 13kbit/s with the channel codec using a further 22kbit/s but this is a very complicated method and so would need a DSP chip with a complex code - far beyond me!
A filter at the output is needed to smoothe the staircase wave form from the DAC and a simple amplifier(not sure of what class) will probably be required to power the speaker. this will enable a onway communication device.
A switching method which u hold when speaking could simplify my coding problem. AS you hold the button a set of warm up bit/s is sent followed by a snync bit and stop bit is sent after the release of the switch( could cause problems with long periods of speech. this switching method would need to be inplace for a 2way radio link and so would be good if i could impliemnt this into my design.
so it sound like i know what im dong and i do to some exstent. but im stuck on the programming. i know i could buy a chip thas does everything ie CVSD etc. But i would like to prog a pic to better my understanding. so im stuck on pic programming
I know that pics can be programmed in C, assembly and hex. And assembly as the benefit of better timing control, i think. but i would like some basic wireless communication code that sets up all the ports/pins etc. so i can consentrate on the modulation. i will test this over a wire link first before adding the fm modules
re RF project thread: **broken link removed**
after reading/researching and your help i know the following.
I need a anti-alising filter after the mic to prevent spectral repetitons. i have decided to go for a 5 or 7 order chebyshev with a .5 db ribble. this has a good steep curve which cuts of frequencies below 4Khz which sould stop all anti-alising.
I can get pics with an on board ADCs and UARTs, the 16C74 has a 8 bit A/D and a UART. ok i need a speech codec before the Tx this can be built using the 16C74 and its A/D then writting a few lines of code to encode the bit stream with stop, sync and parity bits depending on my chosen method of encription.
I then need to decode this at the RX end. the Rx will let in a lot of unwanted interference/noise and so the reciver code will be more complicated, as i believe. i need to decode the sent packets of information with some kind of error checking. A warm up signal from the Tx encoder would help be set up the Rx decoder - but unsure
Ok manchester code is 50% efficent has it encodes a 1 with a 1 then the opposite a 0, which doubles the length of the bit stream. i have available data rates of upto 128kbits which should be enough.
The RS232 standard is intended for relatively short (50feet or less), relatively low speeds(19kbit/s) serial communication over a wire. this could work as it is implimented in radio modems, but is not designed for this purpose and so would cause problems.
GSM speech codec use only 13kbit/s with the channel codec using a further 22kbit/s but this is a very complicated method and so would need a DSP chip with a complex code - far beyond me!
A filter at the output is needed to smoothe the staircase wave form from the DAC and a simple amplifier(not sure of what class) will probably be required to power the speaker. this will enable a onway communication device.
A switching method which u hold when speaking could simplify my coding problem. AS you hold the button a set of warm up bit/s is sent followed by a snync bit and stop bit is sent after the release of the switch( could cause problems with long periods of speech. this switching method would need to be inplace for a 2way radio link and so would be good if i could impliemnt this into my design.
so it sound like i know what im dong and i do to some exstent. but im stuck on the programming. i know i could buy a chip thas does everything ie CVSD etc. But i would like to prog a pic to better my understanding. so im stuck on pic programming
I know that pics can be programmed in C, assembly and hex. And assembly as the benefit of better timing control, i think. but i would like some basic wireless communication code that sets up all the ports/pins etc. so i can consentrate on the modulation. i will test this over a wire link first before adding the fm modules