#134 Bidirectional Level Shifter Module

Test a bi-directional 5/3.3V level shifter module.

Notes

3.3/5V level-shifting modules are quite common, as the need to interface 5V microcontrollers with 3.3V devices/sensors (or vice versa) is pretty common. Often these are billed for I²C or SPI, although they are non-specific and can be used for level-shifting any kind of digital signal. Note: yes, digital high/low signals only; they do not provide an analog scaling of voltages.

I got some of these modules from a seller on aliexpress

The modules have two pairs of “transmit” and “receive” lines. It turns out that transmit and receive are handled differently:

• TXD/TXI uses a standard MOSFET level shifting circuit, so is usable in either direction with accurate levels
• RXD/RXI uses a simple voltage divider. This is OK for signals from high side to low side, but not in the reverse direction.

Construction

This circuit is a quick test of their behaviour: a switch in the 5V circuit controlling a load (LED + resistor) in the 3.3V circuit.

This is identical to the test circuit used in the BidirectionalLevelShifter project, which demonstrates the basic FET trick used by these modules.

All good! Now to put them to work…

Credits and References

• BidirectionalLevelShifter - project testing the basic level-shifting FET trick
• modules from a seller on aliexpress
• I²C - wikipedia
• SPI - wikipedia
• Philips Application Note AN97055
• Bi-Directional Logic Level Converter Hookup Guide - excellent resource from sparkfun