I am using the digital data output pin. Also, since I need to send my data 5 times and with a pause of 5 does it mean that I should make my preamble longer?Originally Posted by dhouston
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I am using the digital data output pin. Also, since I need to send my data 5 times and with a pause of 5 does it mean that I should make my preamble longer?
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Serial communication is a female thing, so bear in mind that preamble are needed and some of them may say the size don't make any difference
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Usually 3-5 $AA as preamble is enough. Machester encoding have it's own advantage if you send long data packet. A checksum is also handy.
I don't think the character pacing (pause x) is really needed if you're using a slow baudrate (2400 bauds or so)
a single SEROUT/DEBUG/SEROUT2/HSEROUT line is all you need in many case.
Always make sure your crystal are accurate.
BTW which PIC are you using?
Last edited by mister_e; - 24th April 2007 at 23:49.
Steve
It's not a bug, it's a random feature.
There's no problem, only learning opportunities.
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I'm using PIC16F88. I have 4 $55 and am using Manchester Encoding.Serial communication is a female thing, so bear in mind that preamble are needed and some of them may say the size don't make any difference
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Usually 3-5 $AA as preamble is enough. Machester encoding have it's own advantage if you send long data packet. A checksum is also handy.
I don't think the character pacing (pause x) is really needed if you're using a slow baudrate (2400 bauds or so)
a single SEROUT/DEBUG/SEROUT2/HSEROUT line is all you need in many case.
Always make sure your crystal are accurate.
BTW which PIC are you using?
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So...
oneofthree = jyi1 ???
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You are such a tease...!
oneofthree or jyi1 or whatever your name is (we never got any) I told you before to start one data byte at the time. A complex program is hard to debug especially if there are serial com's.
Also do not manchester encode the preambles. Only the data bytes and CRC or Checksum.
Ioannis
Last edited by Ioannis; - 25th April 2007 at 08:48.
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I looked back at some previous projects I have done with wireless comms. I have not used the Laipac modules, but have used the RFPICs and the Radiotronix modules.
I have used 1200 baud with one preamble, two start-of-transmission identifiers (STX), and one end-of-transmission (ETX) identifier. The packet data is between these wrappers. In my experience the manchester coding did not help much with short messages.
The only thing I was able to find was the following comments in my code:
My point is, have you tried your code with T2400 (as opposed to N2400)?Code:/* for wireless link, the "invert" option should not be used as this causes the transmitter to iddle on */
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The Radiotronix RCR receivers are clones of the Wenshing/Laipac receivers. The only difference is they number the pins in reverse order. I think Radiotronix gets them from Cansec in China.
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T2400 doesn't really help.
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I would use a 5ms pulse as the preamble and a 20ms pause between data packets (it allows the AGC and threshold to reset).
On the receiving end I would use PulsIn to wait for the 5ms pulse and then go into the normal receive routine once it's received. Using some type of error detection (e.g. checksum) is a necessity.
What range do you need? How much data do you need to send?
Looking at the digital data pin with a 'scope (or recording it with a soundcard as I suggested earlier) can eliminate a lot of guesswork by telling you whether your signal strength is adequate. I find it invaluable.
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I'm curious as to why you use the 20ms pause between packets? I know you said that the pause would reset the AGC & threshold, and that certainly makes sense. But I would figure if you're continuously sending bi-phase encoded data (manchester encoded) practically non-stop, wouldn't everything stay where it would need to be?
EDIT: (add)
I suppose if the TX and RX were changing positions relative to each other, the signal strength would vary, and maybe the AGC/threshold wouldn't 'keep up' with the varying conditions. The 20ms pause would compensate. If that's the case, then it really makes a lot more sense to me.
Last edited by skimask; - 25th April 2007 at 04:46. Reason: Thought about it for a bit...
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AGC reduces the gain as the signal gets stronger. Repeating the signal at close intervals can cause the gain to taper off, resulting in poorer reception. A gap between transmissions lets it reset to its baseline. You can play with the duration of the gap - in this case 5-10mS is probably adequate but its hard to say without hands-on experience to determine typical signal strength and performance. Also, I'm eliminating the manchester encoding - the NEC protocol assures a relatively balanced ratio of pulses/spaces for the dataslicer threshold.
Another reason for inserting a gap is to allow the receiver time to analyze what it has received and decide what action to take.
It is possible to get a measure of signal strength by taking ADC readings of the receiver's Linear output pin. I measure the difference between a pulse and space which, while it is not an absolute measure (due to AGC), gives a good relative indication of signal strength. IOW, if one signal registers 700 and another 500 I know which signal is stronger (and can use it for tuning) but I cannot definitively compare measurements from separate receivers since I'm not measuring an absolute magnitude.
Last edited by dhouston; - 26th April 2007 at 14:28.
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Everything you said makes perfect sense to me. And it might also explain a few issues I've always had with a couple of my RF projects and lengthy/continuous packet transmissions getting dropped after a few seconds of transmitting. I'm going to try your 'pause between packets'/'making the packets smaller' idea and see what happens.
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I can understand that the issues you had might be module related. I never had any problems with FM modules and the ones I designed with the classic slicer approach (given that the proper transmission rules are followed). A good receiver should work 24/7 with no problem.
Ioannis
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It's not really 'problems' I have with the modules. They work fine for me, in bursts. I have a couple of project where one of my remotes acts sort of like a volume control and I have to continuously hold the transmit button down to get the receiver to change, takes about 15 seconds to run from one end to the other. About 3 or 4 seconds into holding the button, it craps out. If I release the button for less than a second and press it again, it'll work for another 3-4 seconds, then repeat. Again, no real problems, and I have a feeling that dhouston's hints earlier may solves this issue.
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Agreed - but these are $5 (retail at Mouser Electronics) superregenerative ASK receivers with a maximum data rate of 4800bps.
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Almost all of my experience is with these specific superregenerative ASK receivers (at various frequencies) or with very similar superregenerative receivers. My suggestions may not apply if you're using more sophisticated receivers (e.g. superheterodyne) or FSK. Most of my applications send/receive 2-3 payload bytes. I think a wireless RS232 link and manchester encoding is overly complicated for such simple needs. If there's a need to send lengthy text or data streams, a superheterodyne or FSK receiver and a wireless RS232 link may make more sense.
I cited the following web page earlier in the thread.You can see the effects of AGC on the initial pulse in the top trace of the first 'scope screenshot. The slope is from the AGC reacting to the wide pulse. You can see the slope starting in the other direction after the pulse ends. If you look a a lot of 'scope screenshots you'll see the same (less pronounced) effect even between the data pulses and see more pronounced differences between a closely spaced series of 0-bit (narrow space) versus 1-bit (wider space). Of course, it's affected by the absolute pulse space widths as well.
The bottom picture is of a signal captured as a .WAV file with a soundcard. You can see that it's more difficult to discern a signal when it has no pronounced initial pulse to set the AGC. In this case, it's the signal sent by a Pronto touchscreen to a Philips RF extender. The three copies of the preamble contain information to address a specific RF extender and set its carrier frequency, etc. which must precede the actual IR code the extender is meant to relay. Philips doesn't use a superregenerative reveiver and they take other steps to improve reception (double modulation) but the picture illustrates the weaknesses of using no preamble or a narrow lead-in pulse with a superregenerative receiver.
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REG: ISM band and the WMTS band
Hi,
Any idea or estimation that are available towards the usage of the ISM band (2.4Ghz to 2.48Ghz) and the WMTS (Wireless medical telemetry service) band ( 608MHZ to 614MHZ, 1395MHZ to 1400MHZ) in the next coming decade for the purpose of the wireless communication implementation.
It would be really great if any info available towards the same is linked to me, [email protected].
Thank you.
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Is the code that I wrote below what you are trying to tell me?
I am only trying to send 4 bits (8 bits encoded). I looked at the digital data pin of the scope and my signal has an amplitude of about 3.72 v.
Transmit:
Pulsout PORTB.7, 500
Pause 20000
serout PORTB.7, n2400, [$aa,encoded2]
Pause 20000
Receive:
Wait55:
Pulsin PORTB.0,1,ct55
If ct55 = 500 Then
goto Waitaa
Else
goto Wait55
Endif
'goto Wait55
Waitaa:
serin PORTB.0, n2400, encoded1
If encoded1 <> $aa Then goto Maina
serin PORTB.0, n2400, encoded1
write 0, encoded1
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Yes, more or less. I would change it to...
The important thing with the signal is that it be clean with no noise pulses interspersed with the data.Code:Transmit: Pulsout PORTB.7, 500 Pause 2500 'shorten space serout PORTB.7, n2400, [$aa,encoded2] Pause 20000 Receive: Wait55: Pulsin PORTB.0,1,ct55 If ct55 < 450 Then Wait55 goto Waitaa
With only 4 bits, I think I would use a variation of the NEC protocol, sending only 1 byte with each code. The NEC protocol has error detection built in so you can discard any corrupted codes. Read the NEC protocol documentation in the link I cited earlier and if you still have questions I'll try to answer them here.
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I tested out the above code thats included in my code and it does not work by wireless or by wire.
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I'm not going to try to read your unformatted code or write the entire application but here are code snippets that show you what you need to do. It sends 4 bits both "as is" and as bitwise complement using a variation of the NEC protocol. I've hardcoded the 4 bits of data as 1101. This is adapted from code I use to send and receive 2-4 bytes so the pins are the ones I used. There are more efficient ways to do things but I've tried to show it step-by-step so you see the logic.
Code:'-----Transmit----- SendRF: wb.0=data0 '00000001 wb.1=data1 '00000001 wb.2=data2 '00000101 wb.3=data3 '00001101 wb=~wb '11110010 wb=wb<<4 '00100000 wb.0=data0 '00100001 wb.1=data1 '00100001 wb.2=data2 '00100101 wb.3=data3 '00101101 'bits 0-3=data, bits 4-7=~data Low 4 For c=1 To Copies PulsOut 4, 500 PauseUs 2500 For i=0 To 7 PulsOut 4, 50 If wb.0=1 Then PauseUs 1500 Else PauseUs 500 EndIf wb=wb>>1 Next PulsOut 4, 50 Pause 20 Next '-----Receive----- DEFINE PULSIN_MAX = 550 RcvRF: PulsIn GPIO.1, 1, STX wb=0 If STX<450 Then RcvRF While GPIO.1=0:Wend For i = 0 To 7 PulsIn GPIO.1, 0, space If (space<40) Or (space>175) Then RcvRF If (space>75) Then wb.0=1 EndIf wb=wb<<1 Next i comp=wb>>4 wb=wb & 7 If wb + comp = 15 Then 'wb is good data Else 'wb is corrupt EndIf
Last edited by dhouston; - 25th April 2007 at 21:59.
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If I were to run your code to test it would I code data0=0000001, data1=00000001, data2=00000101, data3=00001101 and then code data0=001000001, data1=00100001, data3=00100101, data3=00101101? Also in the for c=1 to Copies, what is Copies supposed to mean?Also, I discover that when I use my old code and send it through once and view the digital output of the receiver and transmitter input the on the oscilloscope the sequence appears but it does not get picked up by the microcontroller.
Last edited by jyi1; - 25th April 2007 at 23:26.
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