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<section id="how-does-it-work">
<h1>HOW DOES IT WORK?<a class="headerlink" href="#how-does-it-work" title="Link to this heading"></a></h1>
<p>The BitByteRider RC car is powered by ESP32-C3 Breadboard &amp; Power adapter developmemt board.</p>
<section id="reserved-pins-gpios">
<h2>Reserved Pins &amp; GPIOs<a class="headerlink" href="#reserved-pins-gpios" title="Link to this heading"></a></h2>
<p>The following table summarizes GPIOs and pins reserved for operations purposes.</p>
<p>The GPIO numbers correspond to those on the ESP32-C3 WROOM microcontroller. The Pin number corresponds to the pin on the Breadboard and Power adapter development board.</p>
<section id="x-and-y-axis">
<h3>x- and y- axis<a class="headerlink" href="#x-and-y-axis" title="Link to this heading"></a></h3>
<p>The <strong>GPIO0</strong> and <strong>GPIO1</strong> assigned to measuring the voltage of x- and y- axis of the Joystick. Lastly, there is a group of GPIO pairs responsible for PWM for DC motors.</p>
</section>
<section id="direction-and-speed">
<h3>Direction and Speed<a class="headerlink" href="#direction-and-speed" title="Link to this heading"></a></h3>
<p>The pairs of DC motors on the left side are wired to the dedicated PWM channels. This means that <em>ESP32-C3 Breadboard DevBoard</em> can control rotation speed and direction of DC motors in pairs only (i.e. left and right side).
Consequently, only four PWM channels are sufficient for controlling the direction of the RC car.
Based on this constraint, the RC car can only move front, back, and turn/rotate left and right. Any other movements are not possible (i.e. diagonal or sideways).</p>
<p>A pair of PWM channels are required for defining rotation speed and direction of the DC motors on each side.
In particular, <strong>GPIO6</strong> and <strong>GPIO5</strong> provide PWM to the left- and right- side DC motors to rotate in a <strong>clockwise</strong> direction.
Similarly, <strong>GPIO4</strong> and <strong>GPIO7</strong> provide PWM to the left- and right- side DC motors to rotate in a <strong>counter-clockwise</strong> direction.
Changing PWM on each channel determines the speed and direction of the RC car.</p>
<p>The following images illustrate various PWM duty cycles recorded by oscilloscope.</p>
<br/><br/><br/><br/><table class="docutils align-default">
<thead>
<tr class="row-odd"><th class="head"><p>GPIO</p></th>
<th class="head"><p>Pin</p></th>
<th class="head"><p>Function</p></th>
<th class="head"><p>Notes</p></th>
</tr>
</thead>
<tbody>
<tr class="row-even"><td><p>0</p></td>
<td><p>16</p></td>
<td><p>Joystick x-axis</p></td>
<td><p>ADC1_CH0</p></td>
</tr>
<tr class="row-odd"><td><p>1</p></td>
<td><p>15</p></td>
<td><p>Joystick y-axis</p></td>
<td><p>ADC1_CH1</p></td>
</tr>
<tr class="row-even"><td><p>8</p></td>
<td><p>5</p></td>
<td><p>Joystick push button</p></td>
<td></td>
</tr>
<tr class="row-odd"><td><p>6</p></td>
<td><p>4</p></td>
<td><p>PWM for clockwise rotation of left-side motors</p></td>
<td><p>LEDC_CHANNEL_1</p></td>
</tr>
<tr class="row-even"><td><p>5</p></td>
<td><p>3</p></td>
<td><p>PWM for clockwise rotation of right-side motors</p></td>
<td><p>LEDC_CHANNEL_0</p></td>
</tr>
<tr class="row-odd"><td><p>4</p></td>
<td><p>2</p></td>
<td><p>PWM for counter-clockwise rotation of right-side motors</p></td>
<td><p>LEDC_CHANNEL_2</p></td>
</tr>
<tr class="row-even"><td><p>7</p></td>
<td><p>6</p></td>
<td><p>PWM for counter-clockwise rotation of left-side motors</p></td>
<td><p>LEDC_CHANNEL_3</p></td>
</tr>
</tbody>
</table>
</section>
</section>
<section id="fusion-of-software-with-hardware">
<h2>Fusion of Software with Hardware<a class="headerlink" href="#fusion-of-software-with-hardware" title="Link to this heading"></a></h2>
<p>The <em>struct</em> for storing motors PWM values.</p>
<div class="highlight-c notranslate"><div class="highlight"><pre><span></span><span class="k">struct</span><span class="w"> </span><span class="nc">motors_rpm</span><span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">motor1_rpm_pwm</span><span class="p">;</span>
<span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">motor2_rpm_pwm</span><span class="p">;</span>
<span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">motor3_rpm_pwm</span><span class="p">;</span>
<span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">motor4_rpm_pwm</span><span class="p">;</span>
<span class="p">};</span>
</pre></div>
</div>
<p>The function for updating motors’ PWM values.</p>
<div class="highlight-c notranslate"><div class="highlight"><pre><span></span><span class="c1">// Function to send data to the receiver</span>
<span class="kt">void</span><span class="w"> </span><span class="nf">sendData</span><span class="w"> </span><span class="p">(</span><span class="kt">void</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="n">sensors_data_t</span><span class="w"> </span><span class="n">buffer</span><span class="p">;</span><span class="w"> </span><span class="c1">// Declare data struct</span>
<span class="w"> </span><span class="n">buffer</span><span class="p">.</span><span class="n">crc</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">0</span><span class="p">;</span>
<span class="w"> </span><span class="n">buffer</span><span class="p">.</span><span class="n">x_axis</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">0</span><span class="p">;</span>
<span class="w"> </span><span class="n">buffer</span><span class="p">.</span><span class="n">y_axis</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">0</span><span class="p">;</span>
<span class="w"> </span><span class="n">buffer</span><span class="p">.</span><span class="n">nav_bttn</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">0</span><span class="p">;</span>
<span class="w"> </span><span class="n">buffer</span><span class="p">.</span><span class="n">motor1_rpm_pwm</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">0</span><span class="p">;</span>
<span class="w"> </span><span class="n">buffer</span><span class="p">.</span><span class="n">motor2_rpm_pwm</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">0</span><span class="p">;</span>
<span class="w"> </span><span class="n">buffer</span><span class="p">.</span><span class="n">motor3_rpm_pwm</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">0</span><span class="p">;</span>
<span class="w"> </span><span class="n">buffer</span><span class="p">.</span><span class="n">motor4_rpm_pwm</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">0</span><span class="p">;</span>
<span class="w"> </span><span class="c1">// Display brief summary of data being sent.</span>
<span class="w"> </span><span class="n">ESP_LOGI</span><span class="p">(</span><span class="n">TAG</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;Joystick (x,y) position ( 0x%04X, 0x%04X )&quot;</span><span class="p">,</span><span class="w"> </span><span class="p">(</span><span class="kt">uint8_t</span><span class="p">)</span><span class="n">buffer</span><span class="p">.</span><span class="n">x_axis</span><span class="p">,</span><span class="w"> </span><span class="p">(</span><span class="kt">uint8_t</span><span class="p">)</span><span class="n">buffer</span><span class="p">.</span><span class="n">y_axis</span><span class="p">);</span>
<span class="w"> </span><span class="n">ESP_LOGI</span><span class="p">(</span><span class="n">TAG</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;pwm 1, pwm 2 [ 0x%04X, 0x%04X ]&quot;</span><span class="p">,</span><span class="w"> </span><span class="p">(</span><span class="kt">uint8_t</span><span class="p">)</span><span class="n">buffer</span><span class="p">.</span><span class="n">pwm</span><span class="p">,</span><span class="w"> </span><span class="p">(</span><span class="kt">uint8_t</span><span class="p">)</span><span class="n">buffer</span><span class="p">.</span><span class="n">pwm</span><span class="p">);</span>
<span class="w"> </span><span class="n">ESP_LOGI</span><span class="p">(</span><span class="n">TAG</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;pwm 3, pwm 4 [ 0x%04X, 0x%04X ]&quot;</span><span class="p">,</span><span class="w"> </span><span class="p">(</span><span class="kt">uint8_t</span><span class="p">)</span><span class="n">buffer</span><span class="p">.</span><span class="n">pwm</span><span class="p">,</span><span class="w"> </span><span class="p">(</span><span class="kt">uint8_t</span><span class="p">)</span><span class="n">buffer</span><span class="p">.</span><span class="n">pwm</span><span class="p">);</span>
<span class="w"> </span><span class="c1">// Call ESP-NOW function to send data (MAC address of receiver, pointer to the memory holding data &amp; data length)</span>
<span class="w"> </span><span class="kt">uint8_t</span><span class="w"> </span><span class="n">result</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">esp_now_send</span><span class="p">(</span><span class="n">receiver_mac</span><span class="p">,</span><span class="w"> </span><span class="o">&amp;</span><span class="n">buffer</span><span class="p">,</span><span class="w"> </span><span class="k">sizeof</span><span class="p">(</span><span class="n">buffer</span><span class="p">));</span>
<span class="w"> </span><span class="c1">// If status is NOT OK, display error message and error code (in hexadecimal).</span>
<span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="p">(</span><span class="n">result</span><span class="w"> </span><span class="o">!=</span><span class="w"> </span><span class="mi">0</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="n">ESP_LOGE</span><span class="p">(</span><span class="s">&quot;ESP-NOW&quot;</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;Error sending data! Error code: 0x%04X&quot;</span><span class="p">,</span><span class="w"> </span><span class="n">result</span><span class="p">);</span>
<span class="w"> </span><span class="n">deletePeer</span><span class="p">();</span>
<span class="w"> </span><span class="p">}</span>
<span class="w"> </span><span class="k">else</span>
<span class="w"> </span><span class="n">ESP_LOGW</span><span class="p">(</span><span class="s">&quot;ESP-NOW&quot;</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;Data was sent.&quot;</span><span class="p">);</span>
<span class="p">}</span>
</pre></div>
</div>
<p>The onDataReceived() and onDataSent() are two call-bacl functions that get evoked on each corresponding event.</p>
<p>The rc_send_data_task() function runs every 0.1 second to transmit the data to the receiver.</p>
<div class="highlight-c notranslate"><div class="highlight"><pre><span></span><span class="c1">// Continous, periodic task that sends data.</span>
<span class="k">static</span><span class="w"> </span><span class="kt">void</span><span class="w"> </span><span class="nf">rc_send_data_task</span><span class="w"> </span><span class="p">(</span><span class="kt">void</span><span class="w"> </span><span class="o">*</span><span class="n">arg</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="k">while</span><span class="w"> </span><span class="p">(</span><span class="nb">true</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="p">(</span><span class="n">esp_now_is_peer_exist</span><span class="p">(</span><span class="n">receiver_mac</span><span class="p">))</span>
<span class="w"> </span><span class="n">sendData</span><span class="p">();</span>
<span class="w"> </span><span class="n">vTaskDelay</span><span class="w"> </span><span class="p">(</span><span class="mi">100</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="n">portTICK_PERIOD_MS</span><span class="p">);</span>
<span class="w"> </span><span class="p">}</span>
<span class="p">}</span>
</pre></div>
</div>
</section>
<section id="schematic">
<h2>Schematic<a class="headerlink" href="#schematic" title="Link to this heading"></a></h2>
<img alt="_images/ESP-IDF_Robot_schematic.png" src="_images/ESP-IDF_Robot_schematic.png" />
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<li class="toctree-l1"><a class="reference internal" href="intro.html">INTRODUCTION</a></li>
<li class="toctree-l1 current"><a class="current reference internal" href="#">HOW DOES IT WORK?</a><ul>
<li class="toctree-l2"><a class="reference internal" href="#reserved-pins-gpios">Reserved Pins &amp; GPIOs</a></li>
<li class="toctree-l2"><a class="reference internal" href="#fusion-of-software-with-hardware">Fusion of Software with Hardware</a></li>
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