Understanding hardware triggering requires familiarity with a specific
vocabulary of technical terms. These terms describe the various types of signals, the ways in which signals can be interpreted, and the electrical characteristics
that determine compatibility between components. This article provides a
comprehensive overview of the essential triggering terminology that every
researcher working with scientific cameras should know, particularly those
using cameras with a rolling shutter in camera design.
Digital versus Analogue Triggering
The most fundamental distinction in triggering terminology is between digital
and analogue triggering. Digital triggering involves the transmission of binary
information—represented as either a ‘1’ or a ‘0’—through the alternation
between a high voltage state and a low voltage state. This is by far the most
common form of triggering used in scientific imaging systems. Digital triggers
are well-suited for applications where the primary requirement is to indicate
the occurrence of an event, such as the start or end of an exposure.
Analogue triggering, by contrast, uses the specific voltage value within a
defined range to convey information. For example, an analogue trigger might
use a voltage between -5V and +5V to indicate the desired intensity of a light
source or the target position of a motorized stage. While less common than
digital triggering, analogue triggering offers greater flexibility in applications
where continuous control rather than discrete event signaling is required.
Understanding the rolling shutter in camera systems is particularly important
when selecting trigger types, as the timing requirements differ significantly
between rolling and global shutter sensors.
| Trigger Type | Signal Characteristics | Typical Applications |
| Digital | High/Low voltage states (binary 1/0) | Start/stop exposure, frame triggering, ready signals |
| Analogue | Continuous voltage within a range (e.g., -5V to +5V) | Light source intensity control, stage position control |
Key Digital Trigger Terms
Within digital triggering, several specific terms are used to describe the
behavior and interpretation of signals. Understanding these terms is essential
for correctly configuring triggering setups and diagnosing issues when they
arise.
High and Low Triggers refer to the two voltage states that constitute a digital
signal. In most systems, a high state corresponds to a voltage of +5V or +3.3V,
while a low state corresponds to 0V. However, it is important to note that
different systems may use different voltage ranges, and some components
may operate with voltages ranging from -10V to +10V. Compatibility between
components must be verified to prevent damage.
Edge and Level describe two different ways of interpreting digital trigger
signals. The edge of a trigger is the moment when the signal changes
state—either from low to high or from high to low. Edge-triggered systems
respond at the precise moment of this transition. The level, by contrast, refers
to the period when the signal state is not changing. Level-triggered systems
respond based on whether the signal is in a high or low state, rather than on
the transition between states.
Rising Edge and Falling Edge are specific types of edge triggers. A rising edge
occurs when the signal transitions from a low state to a high state, while a
falling edge occurs when the signal transitions from a high state to a low state.
Many scientific cameras can be configured to respond to either rising or falling
edges, depending on the requirements of the specific application. For example,
the Tucsen Dhyana 400BSI v3 allows users to select the edge sensitivity that
best matches their experimental needs, providing flexibility for a wide range of
triggering scenarios. The rolling shutter in camera systems often requires
careful selection of edge sensitivity to achieve optimal synchronization with
external devices.
Common Hardware Components That Support Triggering
A wide range of optical and experimental hardware components can interact
via hardware triggering, making it a versatile technique for coordinating
complex imaging systems.
| Component Type | Trigger Input Functions | Trigger Output Functions |
| Cameras | Control exposure start/end, frame timing | Indicate exposure state, readiness |
| Light Sources (LEDs, etc.) | Control illumination timing and intensity | Indicate illumination state |
| Lasers | Control laser illumination via AOTFs | Indicate illumination state |
| XY/Z Stages | Control position (analogue) | Indicate movement completion (encoder pulses) |
| Filter Wheels/Cubes | Control switching and movement | Indicate movement completion |
The rolling shutter behavior of CMOS cameras makes them particularly
dependent on well-coordinated triggering, especially when used with external
light sources. This dependency is why many rolling shutter cameras offer
extensive trigger input and output capabilities. The Tucsen Dhyana 400BSI v3 is
one such camera that provides researchers with the tools needed to implement
complex triggering schemes. When evaluating a camera system,
understanding the rolling shutter in camera designs helps researchers
anticipate potential synchronization challenges.
Trigger Standards and Voltage Compatibility
An important consideration in any triggering setup is ensuring compatibility
between the triggering interfaces of different components. The two most
common trigger standards are TTL and optocoupler triggers.
TTL (Transistor-Transistor Logic) triggers are the most widely used standard.
They operate without the need for external power to the triggering interface,
meaning that connecting a camera with TTL outputs to a light source with TTL
inputs typically requires only a single cable between the relevant pins.
Optocoupler triggers are another common interface type. Unlike TTL triggers,
optocoupler triggers require an external power source and a ground point,
typically provided by a permanent 5V and 0V pin from a trigger controller. In
some cases, a resistor may also be required in series with the connection. As
always, consulting the camera manual is essential for correct wiring.
Trigger voltage is another critical factor. While a high state of 5V and a low
state of 0V are the most common configurations, some components produce
higher or lower voltages. Ensuring compatibility between the voltage levels of
different components is essential to avoid damaging sensitive hardware.
Physical Trigger Connectors
Multiple physical connector types are used in hardware triggering systems.
Common examples include SMA, BNC, and SSMA connectors. Some systems
simply use a cable terminating in bare copper wire. In practice, the differences
between these physical interfaces are relatively minor, and adaptors can often
be used to convert between connector types.
