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Bi-Directional Level Converter
Designed by Mark Little
A bi-directional level converter is used to convert signals between (commonly) +5V and +3.3V. This is necessary because different logic families use different operating voltages.

Since many sensors have been built for +5V, the only option, apart from buying sensors that are designed to operate at 3.3V, is to translate the levels. Many microprocessor signals are bi-directional, that is, they can be either an output or an input. As a result, the translation needs to be a two-way process.

For these converters to work, they must be supplied with both the high supply voltage (+5V) and the low supply voltage (+3.3V).
There are many different bi-directional converter boards, but the table below is typical:
Pin Function
HV High Supply Voltage (+5V)
GND High Supply Voltage Earth (GND Pin next to HV)
LV Low Supply Voltage (+3.3V)
GND Low Supply Voltage Earth (GND pin next to LV)
HV1 High Voltage Side of Line 1
LV1 Low Voltage Side of Line 1
... ...
HV4 High Voltage Side of Line 4
LV4 Low Voltage Side of Line 4
Where level translation is required for signal/data/address lines between +5V circuits and +3.3V circuits, bi-directional level converters will be used.