4.6 / 4.7 Using remote input & outputs
The SMC can be controlled remotely, much like it controls the camera, by using Ext 1 inputs. On the left side of the SMC
controller there are two 2.5mm TRS plugs labeled Ext 0 and Ext 1. Each of these plugs breaks out into two I/O lines and
one ground line, which is essential for establishing communication between two electronic components.
The Ext 0 inputs connect directly to the Arduino micro controller's hardware serial pins, and are reserved for special uses
or serial communication. The Ext 1 inputs, however, are general purpose inputs for use in controlling the SMC and
interacting with the environment.
The Basics of SMC Inputs and Outputs
Before we go any further, let’s describe how the SMC inputs work. As we described earlier, there are two I/O lines and
one GND line per input connector, this means there is no 5V signal! In fact, when an input is engaged in the SMC
firmware, it is immediately “pulled high” at 20K of resistance. This means that the SMC will read a 5V signal off that input
as long as the input is left unconnected. Thus, to trigger the input, you will need to connect the GND signal to the input
you wish to trigger. This allows you to wire switches and other passive devices easily without needing a power source.
Only Ext 1 inputs are available for triggering actions on the SMC.
As for outputs, each input port may instead be converted to outputs, to trigger external devices like relays, lights, etc. As
with inputs, the behavior of triggering an output is to connect the given output to the common GND signal.
Actions Available Based On Inputs
Stop
Start
Toggle
Remote Intervalometer
Actions Available for Outputs
Trigger before shot
Trigger after shot
Trigger before and after shot
The trigger times are shared between both outputs if they are configured to trigger at the same time.
Multi-Function Limit Switch
The Multi-Function Limit Switch provide a quick and easy way to interact with the inputs on the SMC. They can be used
either as limit switches, or as remote toggles. For information about how to configure the SMC to work with the switch in
a particular role, see the sections below.
To configure the firmware to recognize your input as a limit switch:
[Enter] to enter the main menu
[Down] to select Settings and press [Enter]
[Down] to select I/O 2 and press [Enter]
[Up] or [Down] to set the value to Stop
[Enter] to save or [Right] to abort
Remote Toggle Switch
Notes:
•
Under no circumstances should you ever send a positive signal (+V) down any Ext I/O line!
•
Doing so may permanently damage your SMC!
Notes:
•
The limit switch function will only work when the program is ‘on’
•
Do NOT rely on limit switches in manual motor control!
•
The input toggles do not apply to manual motor control and you must prevent over-running the belt clips by releasing the
direction button before you hit them.
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