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Dio
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| Sending and Receiving Radio Signals |
 Posted: Tue Apr 27, 2004 4:07 pm |
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Hi all, I'm having some trouble making a remote-controlled car receive the signal from my joystick and wondered if anyone might offer some assistance?
Essentially, I've got a 2-axis joystick (two potentiometers) going in thru one PIC, performing an AtoD conversion, and outputting the results (a number representing forward, back, left or right on a number pad - 8,2,4, or 6) thru the RS232 output to a TWS-434a transmitter.
On the receiving end is a RWS-434 receiver, connected to input pin B0. Here's where it gets kind of tricky, and I'd like to know if maybe the receiver is reading the signal wrong because I'm getting one long string of zeros. My code is below:
| Quote: |
...(header stuff)...
#use rs232(baud=9600,parity=N,rcv=PIN_B0,INVERT,STREAM=signal)
#use rs232(baud=19200,parity=N,xmit=PIN_C6,rcv=PIN_C7,STREAM=pc)
...
...
int8 direction;
// Designate which pins are inputs and which are outputs
set_tris_c(0xc0);
set_tris_b(0x01);
while(TRUE)
{
direction = fgetc(signal);
fprintf(pc,"%d",direction);
if(direction==8) output_c(FWD);
else if(direction==2) output_c(REV);
else if(direction==4) output_c(LEFT);
else if(direction==6) output_c(RIGHT);
else output_c(OFF);
}
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We're using a FPUTC() command to output from the PIC to the transmitter, and using printf statements we know it's outputting the correct number for the car to recognize directions, so we're sort of wondering where the mistake lies? Any help would be appreciated, thanks! |
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Haplo
Joined: 06 Sep 2003
Posts: 659
Location: Sydney, Australia
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| Posted: Tue Apr 27, 2004 5:33 pm |
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| Are you sure you need the 'INVERT' in your #use RS232 statement? Have you tried it without 'INVERT'? |
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Guest
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| Posted: Tue Apr 27, 2004 5:57 pm |
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Without INVERT active, the program collects only 3 or 4 characters and then stops for some reason. I don't see inversion being the problem though, as the output from the transmitter is also inverted in the rs232 serial output.
I guess what I'm asking is pretty much how do I take a character from the transmission PIC and interpret that into a motor control command on the receiver PIC? And how do I keep the flow of data going between the two for direction changes, constant movement, etc?
I found the TWS-RWS combo thru the "Ruf-Bot" project online, but it was written in Basic and ours is in C so there's some differences I can't quite comprehend. Our C Compiler reference book is horrible on this topic as well, and since we're only first-semester Mechatronics students we're just scratching the surface of PIC programming... figured maybe a more seasoned veteran around here could help point us in the right direction? |
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Haplo
Joined: 06 Sep 2003
Posts: 659
Location: Sydney, Australia
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| Posted: Tue Apr 27, 2004 6:32 pm |
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| Anonymous wrote: | | Without INVERT active, the program collects only 3 or 4 characters and then stops for some reason. |
But are those 3 or 4 characters correct values? If so you have to take the INVERT out.
The fact that you are getting a long stream of zeroes indicates that the voltage levels are not being interpreted correctly. I'm not familiar with the RWS-434 chip, but it should be a TTL level RS232 signal. That means a 0v for 0 and a 5v for 1. On idle, the TX line of RWS-434 should be 1, which is 5v. Check the voltage of the TX line when it is inactive and confirm this. If it is 5v, then this is not an inverted serial port.
An inverted port uses 5v for sending 0 and 0v for sending 1. So on idle the TX line of an inverted port is 0v. It is usually used to communicate with a true RS232 device (-10v for 1 and 10v for 0) without a driver chip such as MAX232, to save cost. |
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Humberto
Joined: 08 Sep 2003
Posts: 1215
Location: Buenos Aires, La Reina del Plata
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| Posted: Wed Apr 28, 2004 9:07 am |
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Hola Dio,
| Quote: |
#use rs232(baud=9600,parity=N,rcv=PIN_B0,INVERT,STREAM=signal)
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1) Not so optimistic with this transceiver passband, try at least at 2400 baud.
| Quote: |
Without INVERT active, the program collects only 3 or 4 characters and then stops for some reason. I don't see inversion being the problem though, as the output from the transmitter is also inverted in the rs232 serial output.
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2) Does the received characters == transmited characters?
| Quote: |
I guess what I'm asking is pretty much how do I take a character from the transmission PIC and interpret that into a motor control command on the receiver PIC? And how do I keep the flow of data going between the two for direction changes, constant movement, etc?
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3) Does your project is running properly if you take out the RF link and wire directly Tx ->- Rx modules? As mentioned, take care of the signal polarity, be aware that the receiver PIC (Rx PIN) is expecting a going down pulse as START BIT.
After you solved steps 1 , 2 & 3, you get in the FOURTH problem:
4)Lower AM transceivers requires a balanced signal. Sending unbalanced signals as ASCII chars, the demodulator (in the received side) would get biased improperly and blocked until another string of chars of oposite polarity would recover such situation.
The "clue" is that the "weight" of the equivalent '1' and '0' of your string must be equal. Sending binary ASCII signals over the RF link obviously won´t meet this requeriment.
A) Rigth way to solve this is using Manchester encoding. Not so easy for begginers.
B) A "dirt" an easy solution -if your packet is very short- is to send each ASCII chars precedded by an "balanced" char like 'U' whose binary equivalent is 0b01010101 in this fashion :
Your packet: "G021D"
Sending: "UUGU0U2U1UD"
In the receiver side, just through away the 'U's and tell us your result.
Hope this help,
Humberto |
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Mark
Joined: 07 Sep 2003
Posts: 2838
Location: Atlanta, GA
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