Jumper Soldered - One-Shot Control
Input Polarity
The Servo Trigger input sensitivity can also be changed, using solder
jumper 2 (SJ2).
The default configuration, with no solder applied, configures the Servo
Trigger for use with a normally-open switch, with the internal pull-up resistor
on the microcontroller enabled. This configuration is also suitable for use
with an active-low logic input.
With SJ2 closed, the internal pull-up is disabled, and the input is set as an
active-high logic input.
If SJ2 is closed, be careful about powering up the Servo Trigger when the
input is not connected to anything. When the input is floating, it can
randomly toggle between active and inactive and may cause the motor to
behave unpredictably.
A note about nomenclature here: since the input polarity can be swapped, it
can be hard to talk about – the voltage might be high, but when the sense is
inverted, it indicates that the input isn’t being actuated. To help navigate
this, the polarity-neutral terms active or asserted are used to describe
when the input is being used, and inactive or deasserted to describe the
default state.
More components
The servo trigger can be used with a wider variety of external components
than used in the example above. We used a mid-sized servo, though we
have many other candidates, in a wide variety of sizes & torque ratings.
You can also use different switches, such as micro switches and foot pedal
switches.
Power Notes
Compared to a servo motor, the Servo Trigger board draws very little
current – roughly 5 mA.
The motors draw significantly more – a quick bench test using a small
servo, with only a lightwieght horn attached, shows the motor draws 10 mA
sitting idle, and about 70 mA while moving. Grabbing the horn and twisting
causes the controller to apply current to the motor, counteracting the twist.
It drew 700 mA during this test – a larger servo could draw even more!
These currents can get surprisingly high as you add more motors to the
system – you’ll need to select a power supply with adequate capacity.
The Servo Trigger is designed to make it easy to daisy chain boards – you
can simply connect the VCC and GND pads on adjacent boards.
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