Category: Integrations

What is TTL?

TTL stands for Transistor-to-Transistor Logic, where the “logic” determines which values are high and low.

Standardized common TTL circuits operate with a 5-volt power supply. A TTL signal is defined as low when the voltage is measured between 0.0 V and 0.8 V with respect to the ground terminal, and high when measured between 2.2 V and 5 V (precise logic levels vary slightly between sub-types).

Exacq Hybrid NVR systems and the exacqVision USB I/O Module provide TTL inputs to activate input triggers and create output alarms. This allows exacqVision to interact with external devices/controls which may not provide means to be activated via software integration. The controllers in these systems follow the voltages listed above closely, as shown in the graphic below.

TTL uses a high/low indicator instead of the standard open/closed indicator of a contact closure. Many devices will accept this kind of information; if you have a device that works only with contact closures, you can find devices that convert TTL to contact closure.

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Controlling External Devices with TTL Output

Using Event Linking, exacqVision can activate external devices based on configured events, such as motion detection, analytic object detection, system health, input triggers, and more. See our User Training Videos on Event Linking and Event Monitoring, or refer to the User Manual, for information on configuration.

AC Devices

If you want your exacqVision Server to activate a 120VAC device during an event, it is recommended that you use the Xantech AC-1 switched AC outlet and a 120VAC power source/outlet. Event Linking must also be programmed in the exacqVision Client software.

DC Devices

If you want your exacqVision Server to activate a low-voltage device during an event, it is recommended that you use the Altronix RBSN-TTL relay and a 12-24VDC power supply. Event Linking must also be programmed in the exacqVision Client software.

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Wet and Dry Contacts

Automation and control devices come in countless forms, from different manufacturers, models, and types of devices. But, the general purpose is to turn a circuit on or off to drive a load of some type. In electrical terms a “load” is the end output device. This could be a light bulb or a motor.

When electricity is applied to actuators or relays there is typically some sort of switching involved, whether a physical switch used by a person, a sensor, or a relay. The contacts switch between an open and closed position to either complete the circuit or break the circuit. Additionally, we tend to think of a completed circuit as being “on”, however when using relays our voltage could be applied to the normally open (NO) or the normally closed (NC) contact, which will determine the behavior of the circuit.

DRY CONTACTS require electricity to be sent to the load from some sort of external source. This is the case when using relays, including those found on Exacq Hybrid NVRs or the exacqVision USB I/O Module. Voltage is usually supplied through a “common wire”. In addition, the I/O terminals on many IP Cameras are relays as well.

WET CONTACTS provide power directly, where the current driving the load flows through the switch itself. Consider the circuit breaker panel for your home. The switch on the circuit breaker allows the current to flow through it to power the devices on that circuit.

Exacq Hybrid NVRs and the exacqVision USB I/O module provide both TTL and relay outputs. While TTLs provide electricity directly through solid-state switching, they usually provide too little current to do anything more useful than power a tiny LED, which is why the relay devices mentioned above are used to introduce external current. Whether you use AC or DC will depend on the device you are attempting to control.

Note, that in Figure 1 and Figure 2 above, both modules provide power to the load from an external source. This is required because the output terminals from Exacq do not provide enough voltage or amperage to drive most devices, only enough to signal another device of a change.

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