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Voltage-Level Translation in MCU Projects








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The focus:

Voltage-level translation between the factory floor (24 V) and the logic and between different logic levels (from 5 V down to 0.8 V or even less).

Level-translation between logic and factory floor
A digital controller – basically a computer platform – is connected to an application environment. Such arrangements come in many flavors of size, performance, complexity, and form factor.

How field wiring is attached. To the left, educational examples are shown, to the right, two glimpses into industrial wiring cabinets.

The legacy interface between industrial PCs and mounting racks with I/O modules is a 5-V interface with TTL signal levels.

In typical compact PLCs, the inputs and outputs are rigidly determined by design. A limit switch must be connected to a digital input, a relay to a digital output, a sensor to an analog input, and so on.

With regard to level translation, all those digital controllers, as different as they are, may be represented by one block diagram. The main difference is only in packaging or compactness, respectively.

Translating voltage levels may be required on logic PCBs, too. Our example is an educational module based on an Xmega microcontroller. Its supply voltage is 3.3 V. I/O signals are translated to 5 V and, to support an RS232-Interface, to ± 9 V. A particular challenge was to drive a bidirectional 5-V data bus.


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January 31, 2022

Download the Internet Addendum to the CC article

24-V microcontrollers and CPLDs

Translating 24 volts -- NEW

Level translation between logic signals

Integrated level translators
-- NEW

The 24-V companion - an educational example

Level translation with discrete or SSI components
-- NEW

References and sources