IntermediateInterfaces & Logic
One-Way 3.3 V to 5 V Logic Buffer
Use a 5 V SN74HCT125 to turn 3.3 V logic-high signals into 5 V logic outputs in one direction.
Parts from the database
- SN74HCT125N ร 1Four non-inverting buffers
Other supplies
- breadboardCommon build supply
- 5 V supplyCommon build supply
- 3.3 V microcontroller/signal sourceCommon build supply
- 100 nF bypass capacitorCommon build supply
- 10 kฮฉ input pull-downs as neededCommon build supply
- multimeterCommon build supply
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Connections
- Use the manufacturer's pin diagram for the exact HCT125 package. Connect VCC to +5 V and grounds together; bypass the supply.
- For one channel, connect the 3.3 V signal to A, pull active-low /OE low, and connect Y to a 5 V logic input.
- Tie unused /OE pins high and unused data inputs to a defined level.
- Keep signal direction one-way: this raises 3.3 V logic to 5 V; it is not a 5 V-to-3.3 V down-shifter.
Build steps
- With power off, identify VCC, GND, A, Y, and /OE from the exact package datasheet.
- Power at 5 V and alternate A between ground and 3.3 V.
- Measure Y; it should switch between low and near 5 V.
- Connect Y only to a target rated for 5 V logic.
Software and firmware setup
This is a hardware-only circuit; no firmware is required.
Test your build
A 3.3 V high is recognized by HCT at 5 V; the enabled output swings to the 5 V rail.
Troubleshooting
- No output: /OE is active low; check it is low.
- Y only reaches 3.3 V: check VCC and package pinout.
- Controller resets: verify common ground and make sure the target is not driving Y.
Safety and limitations
Low-voltage digital signals only. Never feed a 5 V output to 3.3 V-only GPIO; use a proper bidirectional translator for two-way traffic.
Manufacturer and platform documentation
Community Notes for This Project
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