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Project Notes

#134 Bidirectional Level Shifter Module

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

The Modules


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.



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…


The Schematic

The Build

Credits and References

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This page is a web-friendly rendering of my project notes shared in the LEAP GitHub repository.

LEAP is just my personal collection of projects. Two main themes have emerged in recent years, sometimes combined:

  • electronics - usually involving an Arduino or other microprocessor in one way or another. Some are full-blown projects, while many are trivial breadboard experiments, intended to learn and explore something interesting
  • scale modelling - I caught the bug after deciding to build a Harrier during covid to demonstrate an electronic jet engine simulation. Let the fun begin..
To be honest, I haven't quite figured out if these two interests belong in the same GitHub repo or not. But for now - they are all here!

Projects are often inspired by things found wild on the net, or ideas from the many great electronics and scale modelling podcasts and YouTube channels. Feel free to borrow liberally, and if you spot any issues do let me know (or send a PR!). See the individual projects for credits where due.