Subject:
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Re: Electrical Data Link between 2 RCXs
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Newsgroups:
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lugnet.robotics.rcx.nqc
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Date:
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Tue, 17 Apr 2001 15:47:39 GMT
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Viewed:
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2762 times
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It's me again with some improvements for an "Electrical Data Link between 2
RCX".
In the current version I changed the default condition of the link to "high"
(in the transmitter: OFF(OUT_B)) so that the receiver has a 1 at its sensor
input. So, you can better see, if the link is active. I also added an UNTIL
(SENSOR_1 == 1) statement in the receiver program (thanks to Dean for that
hint).
In order to get a stable transmission - after a lot of experimenting - I
increased the time for a 1-bit to 40 ms, for a 0-bit to 20 ms. E.g. the
transmission of a "9" (binary 1001) would result in:
_____ ________ ____ _________
________ ____ ________
Startbit bit3 bit2 bit1 bit0
The link works fine, although it is slow. If you need to transmit a value
between 2 RCX very seldom only, you may even transmit 8 bit sensor values.
The original need for the electrical link - transmitting a status from one RCX
to another RCX that should react to it - is of course the better application
for such a slow scheme. In this case, you may perhaps reduce the value range to
2 bits (e.g. 0: stop motor, 1: motor on left, 2: motor on right). This will
allow faster transmissions.
For those, interested in this subject, I will attach the 2 programs for cut &
paste.
Always good connections ...
Bernd Frassek
TRANSMITTER:
int buf = 0; // buffer for value to be transmitted
int mode = 0; // mode for testing transmission
// (0 = contiuos, 1 = single shot by
pressing touch sensor)
task main ()
{
Off (OUT_B); // default condition for electrical link
(high at receiver)
SetSensor (SENSOR_3, SENSOR_TOUCH); // touch sensor for single shots
ClearSensor (SENSOR_3);
SetUserDisplay (buf, 0); // show value being transmitted
while (true) // transmit numbers 0 ... 15 repeatedly
{
buf = 0;
repeat (16)
{
if (mode == 1)
{
until (SENSOR_3 == 1); // single shot mode
until (SENSOR_3 == 0); //
}
send ();
buf ++;
}
}
}
sub send ()
{
#define _one 4
#define _zero 2
int _bit3 = _zero;
int _bit2 = _zero;
int _bit1 = _zero;
int _bit0 = _zero;
// apply bit mask and set bits for transmission
//
if ((buf & 0x08) == 0x08) _bit3 = _one;
if ((buf & 0x04) == 0x04) _bit2 = _one;
if ((buf & 0x02) == 0x02) _bit1 = _one;
if ((buf & 0x01) == 0x01) _bit0 = _one;
// transmit bits
//
Float (OUT_B); Wait (_one); // Startbit (high)
Off (OUT_B); Wait (_bit3); // Bit 3 (low)
Float (OUT_B); Wait (_bit2); // Bit 2 (high)
Off (OUT_B); Wait (_bit1); // Bit 1 (low)
Float (OUT_B); Wait (_bit0); // Bit 0 (high)
Off (OUT_B); // default (low)
Wait (5); // allow enough time for receiver before next
transmission
}
RECEIVER:
int display = 8888; // display variable, default after start = 8888
int xyz; // variable for working with received value
int buf; // buffer for received value
int buf_flag = 0; // flag; = 1, if buffer contains a new received
value
task main ()
{
SetUserDisplay (display, 0);
start receive;
while (true)
{
until (buf_flag == 1); // wait for a new received value
xyz = buf; // store received value
buf_flag = 0; // reset rx_flag
// work with received value
// ...
display = xyz; // here simply display it ...
//
}
}
task receive ()
{
#define _threshold 4 // threshold for pulse length in order to distinguish
betwenn 0 and 1
int _bit3;
int _bit2;
int _bit1;
int _bit0;
int _start;
SetSensor (SENSOR_1, SENSOR_TOUCH);
until (SENSOR_1 == 1); // wait for default condition of link
(high)
// listen to link (receive bits)
//
while (true)
{
buf = 0;
_bit3 = 0;
_bit2 = 0;
_bit1 = 0;
_bit0 = 0;
_start = 0;
until (SENSOR_1 == 0); // wait for Startbit
until (SENSOR_1 == 1) _start ++; // pulse length of Startbit
until (SENSOR_1 == 0) _bit3 ++; // pulse length of bit 3
until (SENSOR_1 == 1) _bit2 ++; // pulse length of bit 2
until (SENSOR_1 == 0) _bit1 ++; // pulse length of bit 1
until (SENSOR_1 == 1) _bit0 ++; // pulse length of bit 0
// only for analyzing the timer values ...
/*
PlayTone(4000, 5);
display = _start;
Wait (100);
PlayTone(4000, 5);
display = _bit3;
Wait (100);
PlayTone(4000, 5);
display = _bit2;
Wait (100);
PlayTone(4000, 5);
display = _bit1;
Wait (100);
PlayTone(4000, 5);
display = _bit0;
Wait (100);
PlayTone(4000, 5);
Wait (50);
*/
// "construct" value according to received bits
//
if (_bit3 >= _threshold) buf = buf + 8;
if (_bit2 >= _threshold) buf = buf + 4;
if (_bit1 >= _threshold) buf = buf + 2;
if (_bit0 >= _threshold) buf = buf + 1;
buf_flag = 1; // new value in buffer
}
}
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Message is in Reply To:
 | | Re: Electrical Data Link between 2 RCXs
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| (...) My guess is that SENSOR_1 in your receiving RCX is getting a 1 when your program starts. I imagine that OFF is the default state for OUT_B in your transmitter RCX, and that the receiver is seeing this before OUT_B is switched to FLOAT. This is (...) (24 years ago, 3-Apr-01, to lugnet.robotics.rcx.nqc)
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