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<h1>Week 7: Electronic Outputs — Final Project MVP</h1>
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The deliverable this week was a Minimum Viable Product for the final project — enough of the system actually running, end-to-end, that the path to the full thing is clear. For my swarm-of-robots project, that meant proving two things in one demo: (1) the radio comms layer can pair two boards and stream packets, and (2) a XIAO ESP32-C3 can actually drive motorized hardware. I had (1) from Week 4 already. (2) was the new piece this week.
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<h2>The MVP setup</h2>
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I didn't have my own three robots built yet, so for the MVP I borrowed an existing two-wheeled robot from my TF Bobby. His robot uses a pair of <b>A4988</b> stepper drivers running bipolar stepper motors — different motor/driver pair than what I'll eventually use on my own final-project robots, but mechanically the same idea (differential drive). I dropped a XIAO ESP32-C3 onto the existing wiring, wrote some quick forward-only stepper code to confirm the steppers responded to my microcontroller, and recorded the result.
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<iframe width="315" height="560" src="https://www.youtube.com/embed/2eCM-E-B1qE" title="Final Project MVP" frameborder="0" allow="accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture; web-share" allowfullscreen></iframe>
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The forward-only sketch I wrote here was deliberately the simplest thing that could possibly work — step both motors at a constant rate, watch the robot roll. I didn't save that exact file as its own sketch; the movement primitives got absorbed into the larger follower sketches I wrote in the weeks after, where they live alongside the RSSI logic.
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<h2>The comms half (carried over from Week 4)</h2>
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The radio side is the same three-sketch trio I built out for Week 4. I'm including them here as well so the MVP is self-contained on this page.
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<a href="mvp_board_addresses.ino" download>mvp_board_addresses.ino</a> — utility: prints the XIAO's MAC address over serial. You flash it once per board on first setup, copy the MAC into the other board's <code>peerAddress</code> array, and never touch it again.
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<a href="mvp_sender.ino" download>mvp_sender.ino</a> — sender: registers the receiver's MAC as an ESP-NOW peer, then broadcasts an incrementing <code>uint32_t packet_id</code> at 5 Hz forever. No sensors, no logic — just a steady heartbeat the receiver can measure RSSI off of.
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<a href="mvp_receiver.ino" download>mvp_receiver.ino</a> — receiver: ingests packets, smooths RSSI over a 10-sample window, and switches a MOSFET-driven DC motor on/off through a hysteresis pair (chase at −45 dBm, stop at −35 dBm). Detailed walkthrough is on the <a href="../04_microcontroller/index.html">Week 4 page</a>.
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<h2>Side experiment: my own (eventually scrapped) DC-motor robot</h2>
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Alongside the MVP I was prototyping the drive electronics for the robot I planned to build myself — a custom differential drive on cheap DC gearmotors driven through an <b>L9110</b> dual H-bridge. The smoke-test sketch below cycles STOP → FORWARD → STOP → SPIN → STOP so I could confirm the wiring and direction sense before flashing the full follower on top of it.
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<a href="mvp_motor_test.ino" download>mvp_motor_test.ino</a>
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<pre><code class="lang-cpp">// L9110 wiring + direction smoke test. No ESP-NOW, no RSSI — just cycles
// STOP → FORWARD → STOP → SPIN → STOP so you can confirm each command
// does what it claims before flashing the full follower.
//
// Expected behavior:
// FORWARD: both wheels turn the same way → robot drives forward
// SPIN: wheels turn opposite ways → robot pivots in place (clockwise)
// If FORWARD goes backward → swap leads on BOTH motors at the L9110 outputs.
// If SPIN drives forward/back → swap leads on ONE motor.
const int LEFT_IA = D2;
const int LEFT_IB = D3;
const int RIGHT_IA = D4;
const int RIGHT_IB = D5;
const int PWM_FREQ = 1000;
const int PWM_RES = 8;
const int SPIN_DUTY = 110;
const int DRIVE_DUTY = 180;
void motorsBegin() {
ledcAttach(LEFT_IA, PWM_FREQ, PWM_RES);
ledcAttach(LEFT_IB, PWM_FREQ, PWM_RES);
ledcAttach(RIGHT_IA, PWM_FREQ, PWM_RES);
ledcAttach(RIGHT_IB, PWM_FREQ, PWM_RES);
}
void motorsStop() {
ledcWrite(LEFT_IA, 0);
ledcWrite(LEFT_IB, 0);
ledcWrite(RIGHT_IA, 0);
ledcWrite(RIGHT_IB, 0);
}
void motorsForward() {
ledcWrite(LEFT_IA, DRIVE_DUTY);
ledcWrite(LEFT_IB, 0);
ledcWrite(RIGHT_IA, DRIVE_DUTY);
ledcWrite(RIGHT_IB, 0);
}
void motorsSpin() {
ledcWrite(LEFT_IA, SPIN_DUTY);
ledcWrite(LEFT_IB, 0);
ledcWrite(RIGHT_IA, 0);
ledcWrite(RIGHT_IB, SPIN_DUTY);
}
void setup() {
Serial.begin(115200);
delay(500);
motorsBegin();
motorsStop();
}
void loop() {
Serial.println("STOP (2s)");
motorsStop();
delay(2000);
Serial.println("FORWARD (2s) — both wheels same direction");
motorsForward();
delay(2000);
Serial.println("STOP (1s)");
motorsStop();
delay(1000);
Serial.println("SPIN (3s) — pivot in place");
motorsSpin();
delay(3000);
}
</code></pre>
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This L9110 + DC plan didn't survive contact with the rest of the project — by the time I was building the actual three-robot fleet I'd pivoted to <b>28BYJ-48 unipolar steppers driven through ULN2003</b> boards (cheaper per unit, runs on a single 5 V rail, simpler to clone three of). The L9110 sketch above is captured here as a historical artifact: useful as a reference for the differential-drive control pattern, not the hardware that actually shipped.
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<h2>What this MVP actually proved</h2>
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<ul>
<li>Two XIAOs can pair over ESP-NOW and stream usable RSSI <i>(already shown Week 4, re-validated)</i>.</li>
<li>One XIAO can drive a real motorized robot platform — at least one I borrowed.</li>
<li>The remaining work for the final is mostly mechanical: build three of my own robots that can carry the same comms + motor stack at the same time.</li>
</ul>
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