Relay Shield
============

The Relay Shield switches two high-power AC or DC loads up to 60 W per relay from the OpenMV Cam, with a 6-36 V input plus an ADC input and a digital I/O line for sync.

.. image:: ../relay-shield-hero.jpg
    :alt: Relay Shield
    :width: 400px
    :align: center

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

Highlights
----------

* Dual relays — 60 W each (15-220 V DC, 125-260 V AC)
* 6-36 V input with reverse-voltage tolerance
* 0-5 V ADC input with ±36 V overvoltage protection
* 0-5 V digital I/O for camera-sync triggers

Pinout
------

.. image:: ../pinout-relay-shield.png
    :alt: Relay Shield Pinout
    :width: 700px

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

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

   "P0",        "Relay 1 control"
   "P1",        "Relay 2 control (alternative)"
   "P2",        "Relay 2 control (default)"
   "P6",        "Level-shifted AIN readback (0–3.3 V on P6)"
   "P10",       "SYN — open-drain digital I/O on the terminal block"
   "PWR in",    "6–36 V wide input on the terminal block (reverse-voltage tolerant)"
   "AIN in",    "Analog input on the terminal block"
   "VIN out",   "5.4 V at up to 600 mA from the on-board regulator"
   "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 front of the shield to switch AIN to a 4–20 mA
   current-loop input.

.. note::

   SYN is an open-drain digital line, pulled up to 3.3 V on the camera
   side and 5 V on the SYN terminal side. By default it's an input —
   the shield level-shifts 0–5 V on SYN 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 SYN.

.. note::

   Each of P0, P1, P2, P6, and P10 can be reclaimed for unrelated
   use. P0, P2, P6, and P10 are connected by default through
   back-side solder jumpers — open the jumper on any pin you want
   to free. P1 defaults to disconnected: bridge its front-side
   jumper to route Relay 2 to P1 instead (and open P2's back-side
   jumper to release P2).

.. note::

   The relays default to normally-open (NO). Solder bridges on the
   bottom of the shield switch them to normally-closed (NC).

Usage
-----

Toggle the two relays from P0 and P1::

    from machine import Pin
    import time

    relay1 = Pin("P0", Pin.OUT)
    relay2 = Pin("P1", Pin.OUT)

    while True:
        relay1.on()
        relay2.off()
        time.sleep(1)
        relay1.off()
        relay2.on()
        time.sleep(1)

Read the AIN terminal-block input through the level-shifted P6 pin::

    from machine import ADC
    import time

    ain = ADC("P6")

    while True:
        v = ain.read_u16() * 3.3 / 65535
        print("AIN:", v * (5.0 / 3.3), "V")
        time.sleep_ms(100)

React to a falling edge on the SYN line — for example, to sync the
camera with another device pulling SYN low::

    from machine import Pin

    def on_sync(pin):
        print("SYN falling edge")

    syn = Pin("P10", Pin.IN)
    syn.irq(on_sync, Pin.IRQ_FALLING)