Nigels Manchester Encoding Tutorial - Electronic Circuits Projects Diagrams Free

cyprio7 · 24th January 2008, 12:42 AM

post deleted

**Nigel Goodwin** · 24th January 2008, 02:28 PM

Quote:

Originally Posted by cyprio7

Sorry I have just remembered something else as well. In transmit tutorial1 for manchester encoding, what oscillator speed has been used, is it 4Mhz? Also what is the baud rate trying to be achieved?

Say for example its 9600, and you want to send bit 1's, you use this code

Baud rate doesn't apply, it's not RS232 - the whole point of Manchester coding is that it doesn't need to be accurately timed.

If it's running on a 16F628, then it's 4MHz, because it uses the internal oscillator.

Can't help you on the CRC though, I didn't write it, I just 'borrowed' the code and modified it for my own uses.

cyprio7 · 24th January 2008, 04:26 PM

Ok that makes sense

bananasiong · 24th January 2008, 04:45 PM

Hi,
I don't think the RF module can handle such high data rate. Some cheaper RF module that I've used has the data rate of only 3000 bps.

**Nigel Goodwin** · 24th January 2008, 06:11 PM

Exactly, it's a question of what the RF link will handle - but the important thing to remember is that the receive routine isn't looking for specific bit lengths, it's looking for transitions from 0 to 1, and from 1 to 0.

**Nigel Goodwin** · 3rd February 2008, 04:12 PM

Again, they come from the original source, but you simply comment out the ones you don't want - the inverse ones are commented out above.

**Nigel Goodwin** · 4th February 2008, 06:02 PM

Try reading the MPASM/MPLAB helpfile!, in particular conditional assembly, with ifndef, else and endif.

cyprio7 · 4th February 2008, 07:08 PM

Quote:

Originally Posted by Nigel Goodwin

Try reading the MPASM/MPLAB helpfile!, in particular conditional assembly, with ifndef, else and endif.

will do

.......

**Nigel Goodwin** · 10th February 2008, 06:13 PM

It's not transmitting at any specific baud rate, and you are correct that Manchester coding at least halves the effective baud rate.

The routines 'as is' should work fine, try them and see. Bear in mind, you're not sending continuous data, but packets of data.

**Nigel Goodwin** · 10th February 2008, 10:18 PM

Like I said, try it and see, it should work fine - and forget baud rate, it doesn't apply - that's the whole point of Manchester.

**Nigel Goodwin** · 19th February 2008, 07:59 PM

The transmitter just sends a plain carrier, so doesn't cause any problems if there's no data being sent. Turning the transmitter OFF makes it worse, as the receiver is flooded by noise then, but the Manchester routines ignore it.

Just send the data as packets, separated by enough time to send all the data out as RS232.

**Nigel Goodwin** · 28th February 2008, 10:33 AM

If you're wanting duplex operation, I would suggest you get a transceiver module, rather than separate receiver and transmitter - this will have the required switching between the two. It's not just a matter of connecting them together, you would upset the loading on both - the usual method is to use PIN diode switches, which select the correct connection automatically.

**Nigel Goodwin** · 28th February 2008, 12:29 PM

Quote:

Originally Posted by cyprio7

how about if i connect vdd of the transmitted to ra0 on the PIC, the vdd of the reciever to ra1. The reciever is usually on and transmitter off, which means ra1=on ra0=off. When i want to transmit something, i can turn ra1=off, and make ra0=on, then transmit. Because only one of the modules are only ever on at one time, it should be seen as an open circuit by the rest of the circuit, therefore not affecting the load if rx and tx are using the same antenna? Will this work do you think?

Power makes no difference, both are still connected to (and loading) the aerial.

Quote:

Please tell me what type of antenna you used or that you recommend.

I've simply used a piece of wire as a 1/4 wave whip.

**Nigel Goodwin** · 19th March 2008, 10:56 AM

I've only used the ones in my tutorial, I can only suggest you check the datasheets and see what they say.

**Nigel Goodwin** · 10th April 2008, 07:45 PM

Quote:

Originally Posted by cyprio7

hi nigel, just wanted to ask a couple of questions about your schematic for the RF transmitter board. You have used a 10k resistor, with one end being connected to 5V power rail, and the other end going into the data input of the tx module which requires 3.3V. If the input impedance to the data pin is very high, isnt almost all of the 5V dropped over the resistor therefore making almost 5V appear on the pin instead of 3.3V? i think im wrong so please could you explain how this works?

The input pin has protection diodes (like a PIC does), the 10K limits the current and the diodes clip the 5V signal to 3.3V.

Quote:

also reguarding the 3.3V zener diode you have used, why did you have to use a 68ohm resistor with that? could you not just use the zener diode by itself reverse biased to provide max voltage of 3.3V, seeing as the module will draw as much current as it needs anyway, why do you need to limit the current with the 68 ohm resistor?

Because without the 68 ohm the zener will short out the 5V rail, overheat very quickly, and go S/C itself - you MUST have a current limiter feeding a zener diode.

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24th January 2008, 12:42 AM	(permalink)
cyprio7	circuit post deleted __________________ life\'s a bitch then u marry one. ) Last edited by cyprio7; 10th May 2008 at 01:00 AM.

24th January 2008, 04:26 PM	(permalink)
cyprio7	Ok that makes sense __________________ life\'s a bitch then u marry one. ) Last edited by cyprio7; 10th May 2008 at 01:04 AM.

24th January 2008, 04:45 PM	(permalink)
bananasiong	Hi, I don't think the RF module can handle such high data rate. Some cheaper RF module that I've used has the data rate of only 3000 bps. __________________ Superman returns..

24th January 2008, 06:11 PM	(permalink)
Nigel Goodwin	Exactly, it's a question of what the RF link will handle - but the important thing to remember is that the receive routine isn't looking for specific bit lengths, it's looking for transitions from 0 to 1, and from 1 to 0. __________________ PIC programmer software, and PIC Tutorials at: http://www.winpicprog.co.uk

3rd February 2008, 04:12 PM	(permalink)
Nigel Goodwin	Again, they come from the original source, but you simply comment out the ones you don't want - the inverse ones are commented out above. __________________ PIC programmer software, and PIC Tutorials at: http://www.winpicprog.co.uk

4th February 2008, 06:02 PM	(permalink)
Nigel Goodwin	Try reading the MPASM/MPLAB helpfile!, in particular conditional assembly, with ifndef, else and endif. __________________ PIC programmer software, and PIC Tutorials at: http://www.winpicprog.co.uk

10th February 2008, 06:13 PM	(permalink)
Nigel Goodwin	It's not transmitting at any specific baud rate, and you are correct that Manchester coding at least halves the effective baud rate. The routines 'as is' should work fine, try them and see. Bear in mind, you're not sending continuous data, but packets of data. __________________ PIC programmer software, and PIC Tutorials at: http://www.winpicprog.co.uk

10th February 2008, 10:18 PM	(permalink)
Nigel Goodwin	Like I said, try it and see, it should work fine - and forget baud rate, it doesn't apply - that's the whole point of Manchester. __________________ PIC programmer software, and PIC Tutorials at: http://www.winpicprog.co.uk

19th February 2008, 07:59 PM	(permalink)
Nigel Goodwin	The transmitter just sends a plain carrier, so doesn't cause any problems if there's no data being sent. Turning the transmitter OFF makes it worse, as the receiver is flooded by noise then, but the Manchester routines ignore it. Just send the data as packets, separated by enough time to send all the data out as RS232. __________________ PIC programmer software, and PIC Tutorials at: http://www.winpicprog.co.uk

28th February 2008, 10:33 AM	(permalink)
Nigel Goodwin	If you're wanting duplex operation, I would suggest you get a transceiver module, rather than separate receiver and transmitter - this will have the required switching between the two. It's not just a matter of connecting them together, you would upset the loading on both - the usual method is to use PIN diode switches, which select the correct connection automatically. __________________ PIC programmer software, and PIC Tutorials at: http://www.winpicprog.co.uk

19th March 2008, 10:56 AM	(permalink)
Nigel Goodwin	I've only used the ones in my tutorial, I can only suggest you check the datasheets and see what they say. __________________ PIC programmer software, and PIC Tutorials at: http://www.winpicprog.co.uk