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Digital inputs - Lite

Digital inputs serve for an indication of TRUE/FALSE logic states.

Unipi Lite

TRUE logic state (switched on) is indicated by the corresponding LED placed below the inputs.

For connecting external devices to digital inputs, we recommend using a different (separate) power supply in order to retain galvanic isolation.

The software detects TRUE state if the input voltage between the given DIx and DIGND terminals is in range of 7-24 V⎓. If the voltage decreases below 3 V⎓, the FALSE state is indicated. The voltage between 3-7 V⎓ is detected as a non-defined state.

Each digital input connector features common DIGND terminal. When using the internal power supply, the terminal is unused. If you wish to use an external power supply for DIs, you need to set switches accordingly first (see DIP switch settings. Only then it is possible to connect the power supply's negative pole to DIGND. The source's positive pole is to be connected through the external device via DIx terminal.

Connection of DI with the internal power supply:

Connecting DI with an external power supply:
Always set DIP switches first before connecting an external power supply

Connecting DI with both external and internal power supplies:
Set DIP switches before connecting the external power supply. You can connect it to any I/O group.

Counter input
One of the most interesting functions is counter input - a high-speed rising edge counter independent on the control software. Simply put, the counter can very accurately detect even very short pulses.

Counter inputs are suitable especially for collecting data from energy meters, water meters, gas meters and other pulse meters installed in HVAC systems. They are also useful for reading engine revolutions. For this purpose, Unipi units feature 64-bit registers. When the maximum value of the counter (4 294 967 295) is exceeded, the counter resets to 0. Counter inputs can be used at up to 10 kHz frequency; in the Mervis IDE library devices, they are labelled as CNT inputs.


On Unipi 1.1 and Unipi 1.1 Lite the counter resets when the power supply is unplugged. This function needs to be configured in the control SW.

DIP switch settings:
An external power supply can be used to power digital inputs. This setup is available through a correct setting of DIP switches A and B. Using external power supply includes galvanic isolation of digital inputs. The Unipi 1.1 Lite board must be unplugged from power during the DIP switch configuration. After finishing the setup and connecting the negative pole of the external supply (see below), you can plug in the board's power source.

By default, the DIP switches A and B are set to ON. Digital inputs are connected to a 12 V⎓ internal power supply:

DIP switch A is set to OFF, DIP switch B is set to ON. Digital inputs of the A group (ie. DI1 to DI3) are now ready for connection of an external power supply. Group B inputs are still powered by the 12 V⎓ internal supply.

This is possible also in reverse → DIP switch A is set to ON, DIP switch B is set to OFF. Digital inputs of the A group are now powered by the internal 12 V⎓ source, group B inputs are ready for connection of an external power supply.

If both DIP switches A and B are set to OFF, digital inputs of both A and B groups (DI1 to DI6) are ready for connection of an external power supply:

Input type SINK
Input terminals DIx (where x represents the terminal's number)
One common ground for DI1-3, second common ground for DI4-6 DIGND (serves as a negative pole for external power supply)
Number of inputs 6
Maximum voltage for log. 0 3 V DC
Minimum voltage for log. 1 7 V DC
Maximum voltage 24 V DC
Power supply switches for DI A, B
Internal 12 V DC power supply positive pole (only for DI) 12 V
Galvanic isolation Yes (if an external power supply is used)