Serge NOEL
154 lines
8.4 KiB
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154 lines
8.4 KiB
Plaintext
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<title>Hardware support: Multi-bit and Byte Communication Using CMRI</title>
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<!-- Copyright 2020 Jerry Grochow -->
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<meta name="author" content="Jerry Grochow">
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<meta name="keywords" content="Arduino CMRI JMRI Byte Communication">
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<h1>Hardware support: Multi-bit and Byte Communication Using CMRI and arduinos</h1>
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<div class="para">
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<p>JMRI implements the <a href="../cmri/CMRI.shtml">CMRInet protocol</a> to send and
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receive information via changing the state of JMRI objects:</p>
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<ul>
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<li>sending to a CMRI node that a turnout should be thrown or a light turned on or off
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(any accessory attached to a CMRI output),</li>
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<li>receiving from a CMRI node to indicate that a sensor has become active or inactive
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(any CMRI input).</li>
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</ul>
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<p>JMRI objects are associated with a single CMRI bit in the case of sensors (input) and
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lights (output), and one or two bits in the case of turnouts (see the CMRI help page
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<a href="../cmri/CMRI.shtml#L405">section on setting up turnouts and lights</a> for use
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with CMRI). With the introduction of microcontroller technology such as the <a href=
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"https://www.arduino.cc/" target="_blank">arduino</a> CMRI nodes need no longer be restricted to
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operate layout hardware based on single (or two) bit commands. Arduinos are quite capable
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computers that can process CMRINet messages and act on what they receive under local
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program control. <a href="index.shtml#CMRI">An arduino emulating a CMRI node</a> can be
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programmed to start animations, play a series of sounds, light buildings in a realistic
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way, or control the speed of accessory motors -- just about anything the modeller can dream
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up.</p>
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<p>Similarly, it is also possible to send information back to JMRI over CMRINet in the form
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of numbers or letters, or any string that can be encoded in a few bytes of information.
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JMRI would receive each byte as setting the state of eight sensors, but a simple JMRI
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script can translate that binary information into the decimal number or character it
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represents.</p>
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<p class="note">It is also possible to send numbers and characters directly to JMRI from
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arduinos by using <a href="index.shtml#serial">serial communications</a> without taking
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advantage of JMRI's CMRInet capabilities. Each approach has its advantages and
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disadvantages, as discussed <a href="index.shtml#connect">here.</a></p>
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<p class="im"><img src="images/CMRISensorsByte.png" class="floatLeft" height="165" width=
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"275" alt="Sensor Table with 8 sensors> Create eight sensors"> One example of this type
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of usage would be using two JMRI lights (connected to one CMRI bit apiece) to tell the
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arduino to either increase or decrease the speed of a motor attached to an animation
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(perhaps a rotating carousel). The arduino can change the speed of the motor and then send
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back a number indicating the current speed (perhaps 1 to 8) by encoding that number in
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several bits to be sent as part of the CMRINet transmission. A <a href=
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"../../tools/scripting/index.shtml">JMRI script</a> can be <a href=
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"../../tools/scripting/HowTo.shtml#multturnouts">listening to changes</a> in these "speed"
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bits and use them to create a decimal number in a <a href=
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"../../tools/Memories.shtml"></a>JMRI memory variable for display on a panel, as
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illustrated in a <a href="https://www.jmri.org/jython/CmriBitsToBytes.py" target=
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"_blank">this example script.</a> The image here shows sensors 0, 1, 2, and 3 active which
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would translate into the decimal number 15.</p>
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<p class="im"><img src="images/CMRINode-MotorControl.png" alt=
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"Example Panel Using Bit Display" class="floatRight" height="225" width="135">
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Alternatively, a number of sensor bits can be allocated to a speed display with the arduino
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activating the sensors to indicate percentage of maximum speed, as shown in the layout
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panel image. Four of the eight bits of this carousel speed control are "lit" or active,
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representing a speed of 50% of maximum. The panel also shows the on-off slider control and
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clickable greater-than/less-than signs to command the arduino to run the carousel faster or
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slower. The bottom part of the panel shows another example with a curved arrow which when
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clicked tells the arduino to change the direction of the attached Ferris wheel (currently
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off).</p>
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</div>
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<div class="list">
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<h1>Example of JMRI setup</h1>
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<p>The steps are fairly straightforward:</p>
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<dl>
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<dt class="left">Configure a CMRI node</dt>
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<dd class="first">
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<p><a href="../cmri/CMRI.shtml#L268">Configure a CMRI node</a> representing the number
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of output bits (JMRI-&gt;CMRI node) and input bits (CMRI node-&gt;JMRI)
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desired. Remember that <a href="../cmri/CMRI.shtml#L391">JMRI lights and turnouts
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output to CMRI and JMRI sensors provide inputs</a> (think of it in terms of the CMRI
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node: physical sensors input information to the node; the node then outputs information
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to control physical turnouts and lights).</p>
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</dd>
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<dt class="left">Create light objcts</dt>
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<dd>
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<p>Create as many <a href="../../tools/Lights.shtml">JMRI lights</a> as you need to
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tell the arduino to perform some task. Controlling whether a motor is on or off can be
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done with a single light (INACTIVE (which sends a 0) for OFF, ACTIVE (which sends a 1)
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for ON). Controlling its speed requires two lights - one to tell it to increase, one to
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tell it to decrease, neither on to stay the same speed.</p>
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</dd>
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<dt class="left">Create sensor objects</dt>
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<dd>
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<p>Create <a href="../../tools/Sensors.shtml">sensors</a> as shown above for each byte
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of information (number or character) you want to receive back from the arduino. If you
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want to receive the motor speed as a number from zero to seven, you need three sensors.
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If you want to receive larger numbers, you need more sensors to get more bits. Eight
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bits can represent numbers up to 255 (the picture here shows bits corresponding to the
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decimal number 14). Make sure the sensors are linked to the appropriate bits on your
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arduino/CMRI node.</p>
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<p class="note">While JMRI sends and receives a 0 or 1 in the CMRI bit steam, it
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translates a zero into a sensor INACTIVE state, which is actually stored as 4
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(requesting "state" and printing it as a number in a script will return a 4) and ACTIVE
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as a 2. This is important in writing your JMRI script to translate received
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sensor states as binary bits.]</p>
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</dd>
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<dt class="left">Create memory variable</dt>
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<dd>
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<p>Create <a href="../../tools/Memories.shtml">memory variable</a> to hold each byte of
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information that will be computed by the script from the eight sensors.</p>
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</dd>
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<dt class="left">Run script</dt>
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<dd>
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<p>Create <a href="../../tools/scripting/HowTo.shtml#multturnouts">a listening
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script</a> as discussed above to translate the sensor states into bits and create a
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number of letter in the memory variable. An example script to convert eight sensor
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states (bits) into a number can be found <a href=
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"https://www.jmri.org/jython/CmriBitsToBytes.py" target="_blank">here.</a></p>
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</dd>
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</dl>
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