Servo Shield
============

The Servo Shield (v3) drives up to four standard hobby servos directly from the OpenMV Cam. Its on-board regulator accepts a 6–36 V input on the terminal block and delivers 5.6 V at up to 5 A — enough to power both the camera and the servos from a single supply.

.. image:: ../servo-shield-hero.jpg
    :alt: Servo Shield
    :width: 400px
    :align: center

For full datasheet, photos, and ordering see the
`Servo Shield product page <https://openmv.io/products/servo-shield-v2>`_.

Highlights
----------

* Drive up to four hobby servos via P7 / P8 / P9 / P10
* 6–36 V input on the terminal block (reverse-voltage tolerant)
* 5.6 V at up to 5 A on VIN — powers the camera and servos
* 0–5 V ADC input with overvoltage protection up to ±36 V
* Bidirectional 0–5 V digital I/O with 3.3 V to 5 V level shifting

Pinout
------

.. image:: ../pinout-servo-shield.png
    :alt: Servo Shield Pinout
    :width: 700px

Pin reference
-------------

.. csv-table::
   :header: "Pin", "Function"
   :widths: 20, 80

   "P6",        "Level-shifted AIN readback (0–3.3 V on P6)"
   "P7",        "Servo 1 — bidirectional 3.3 V ↔ 5 V GPIO"
   "P8",        "Servo 2 — bidirectional 3.3 V ↔ 5 V GPIO"
   "P9",        "Servo 3 — bidirectional 3.3 V ↔ 5 V GPIO"
   "P10",       "Servo 4 — bidirectional 3.3 V ↔ 5 V GPIO"
   "PWR in",    "6–36 V wide input on the terminal block (reverse-voltage tolerant)"
   "AIN in",    "Analog input on the terminal block"
   "VIN out",   "5.6 V regulated, up to 5 A combined for servos and camera"
   "3.3V rail", "Powers the shield's on-board electronics"
   "GND rail",  "Common ground"

.. note::

   AIN is overvoltage-protected up to ±36 V and defaults to a 0–5 V
   voltage input, scaled down to 0–3.3 V on P6. Bridge the 4–20 mA
   mode shunt on the back of the shield to switch AIN to a 4–20 mA
   current-loop input.

.. note::

   Each of P6–P10 is tied to the camera through a 0-ohm resistor on
   the back of the shield. Remove the resistor on any pin you want to
   reclaim for unrelated use.

.. note::

   On the v2 version of the shield, P6–P9 are unidirectional
   3.3 V → 5 V level shifters (output only). P10 is an open-drain
   digital line, pulled up to 3.3 V on the camera side and 5 V on the
   servo-pin side. By default it's an input — the shield level-shifts
   0–5 V on the servo pin down to 0–3.3 V on P10. Change the on-board
   solder jumper to flip P10 into an output, level-shifting 0–3.3 V on
   P10 up to 0–5 V on the servo pin.

Usage
-----

Drive a hobby servo from any of P7–P10 with a 50 Hz PWM signal. The
pulse-width range varies between servos, so tune ``MIN_US`` and
``MAX_US`` to match yours — typical values are around 1000–2000 µs::

    from machine import Pin, PWM
    import time

    MIN_US = 1000  # full-left pulse width (microseconds)
    MAX_US = 2000  # full-right pulse width

    servo = PWM(Pin("P7"), freq=50)

    def angle(deg):
        pulse_us = MIN_US + (deg * (MAX_US - MIN_US)) // 180
        servo.duty_ns(pulse_us * 1000)

    while True:
        angle(0)
        time.sleep(1)
        angle(90)
        time.sleep(1)
        angle(180)
        time.sleep(1)

Read the AIN terminal-block input (the level-shifted result appears
on P6)::

    from machine import ADC
    import time

    ain = ADC("P6")

    while True:
        # 0–5 V on the AIN terminal scaled to 0–3.3 V on P6
        v = ain.read_u16() * 3.3 / 65535
        print("AIN:", v * (5.0 / 3.3), "V")
        time.sleep_ms(100)