Electronic modules can connect to a project in many different ways. Three common connector styles are screw terminals, pin headers and STEMMA QT / Qwiic 4-pin I2C connectors. They all move signals and power from one board to another, but they are designed for different situations.
This article compares screw terminals, pin headers and STEMMA QT / Qwiic connectors from a practical project point of view. The goal is to help choose the right connection method for sensors, displays, modules, prototypes, educational kits and finished projects.
Three Very Different Connection Styles
The connector style affects how easy a project is to build, troubleshoot, modify and use safely.
- Screw terminals: best for external wires, power, relays, switches and field connections
- Pin headers: best for breadboards, jumpers, shields and low-cost module connections
- STEMMA QT / Qwiic connectors: best for quick plug-in I2C module connections
There is no single best connector for every project. The right choice depends on wire type, current, mechanical stress, user skill level, serviceability and whether the connection is internal or external.
Screw Terminals: Strong Connections for Real Wires
Screw terminals are widely used when a module must connect to loose wires. They are common in power supplies, relay modules, PLC-style boards, sensor wiring, switches, motors and industrial-style projects.
- Accepts stripped wire ends
- Good for external wiring
- Useful for power and higher-current connections
- Can be tightened and serviced with a screwdriver
- More mechanically secure than loose jumper wires
- Larger than pin headers or STEMMA QT / Qwiic connectors
Screw terminals are a good choice when the connection must survive handling, vibration, field wiring or repeated installation work.
Pin Headers: Simple, Cheap and Flexible
Pin headers are common on Arduino-compatible modules, development boards and breadboard-friendly circuits. They are inexpensive and flexible, but they are not always mechanically secure.
- Low cost
- Breadboard-friendly
- Works with jumper wires
- Good for prototyping
- Easy to probe with test equipment
- Can loosen or be connected incorrectly
Pin headers are excellent for development and experiments. For finished devices, they may need additional support, keyed connectors or strain relief.
STEMMA QT / Qwiic Connectors: Plug-In I2C Modules
STEMMA QT and Qwiic connectors are small 4-pin connectors commonly used for I2C modules. They usually carry GND, power, SDA and SCL. The goal is to make I2C module connections quick, compact and less error-prone than loose jumper wires.
- Small 4-pin connector for I2C modules
- Usually carries GND, VCC, SDA and SCL
- Quick plug-in connection
- Reduces wiring mistakes
- Good for modular sensor and display systems
- Not intended for high-current external wiring
STEMMA QT / Qwiic connectors are very useful when building modular I2C systems with sensors, RTCs, displays, ADCs, DACs and other low-power modules.
Main Comparison Table
| Feature | Screw Terminals | Pin Headers | STEMMA QT / Qwiic |
|---|---|---|---|
| Best for | External wires, power, switches, relays and field connections | Breadboards, jumpers, shields and prototypes | Small I2C modules and modular sensor systems |
| Mechanical strength | Good when tightened properly | Moderate to low with loose jumper wires | Good for small internal module cables, not for heavy wires |
| Ease of use | Good for stripped wires, needs screwdriver | Very flexible, but easy to miswire | Very easy for compatible I2C modules |
| Current capability | Usually best of the three, depending on terminal rating | Moderate, depends on header and contact quality | Low-current signal/module power only |
| Space required | Largest | Medium | Smallest |
| Miswiring risk | Medium, depends on labeling and user care | High with loose jumpers | Low when cables and pinout match the standard |
| Best project stage | Finished wiring and field connections | Prototyping and development | Modular plug-in I2C builds |
| Main limitation | Larger size and slower to connect | Less secure and easy to connect incorrectly | Limited to low-current I2C-style module connections |
Mechanical Reliability
Mechanical reliability matters when wires are moved, pulled or installed in an enclosure. A loose jumper wire may be fine on a workbench but frustrating in a finished device.
- Screw terminals are good for wires entering or leaving an enclosure
- Pin headers are good for prototyping but can loosen
- STEMMA QT / Qwiic cables are good for internal low-power module links
- External cables need strain relief regardless of connector type
For real-world wiring, the connector should match the mechanical stress it will see.
Electrical Current and Power
Not every connector is suitable for power delivery. Small signal connectors are convenient, but they should not be used beyond their current rating.
- Screw terminals are usually better for power inputs and higher-current loads
- Pin headers can carry moderate current but depend heavily on contact quality and pin count
- STEMMA QT / Qwiic connectors are intended for low-current module power and I2C signals
- Relays, motors, heaters and LED strips should not be powered through tiny I2C connectors
For sensors and small modules, STEMMA QT / Qwiic power is usually fine. For loads, use proper power connectors or screw terminals.
I2C Connections
STEMMA QT and Qwiic connectors are especially useful for I2C because I2C normally needs only four wires: power, ground, SDA and SCL.
- Reduces wiring mistakes
- Supports daisy-chaining on many modules
- Works well for sensors, RTCs, displays and small modules
- Keeps modular systems clean
- Still requires attention to voltage, pull-ups and address conflicts
The connector makes I2C easier to wire, but it does not remove normal I2C design rules.
Breadboard and Learning Projects
Pin headers are still very useful in education and prototyping. They fit breadboards, Dupont jumper wires and Arduino-style development boards.
- Easy to change wiring quickly
- Good for experiments
- Good for measuring signals with probes
- Low cost
- Works with many existing modules
For learning, pin headers are hard to beat. The drawback is that messy jumper wiring can quickly become unreliable as a project grows.
Finished Projects and Enclosures
Finished projects need better wiring discipline than bench prototypes.
- Use screw terminals for external wires
- Use keyed connectors or locking connectors where cables may be unplugged
- Use STEMMA QT / Qwiic for internal I2C module connections
- Avoid loose jumper wires inside finished products
- Add strain relief for cables leaving the enclosure
A project that worked perfectly on the bench can fail inside an enclosure if the wiring is not mechanically secure.
Modular Systems
For modular electronics systems, connector consistency is very important. If every I2C module uses the same 4-pin connector and pinout, modules can be connected and rearranged quickly.
This is one reason why STEMMA QT / Qwiic-style connectors are useful in modular systems such as CANABLOX. They allow small I2C modules to connect with short cables instead of loose jumper wires.
- Cleaner wiring
- Faster module changes
- Lower risk of swapping SDA and SCL
- Better for education and demonstrations
- Less breadboard clutter
For external signals such as switches, relays, power and field wiring, screw terminals can still be the better choice on the same module system.
Connector Size and Board Space
Connector choice affects PCB size. Screw terminals take much more space than pin headers or STEMMA QT / Qwiic connectors.
- Screw terminals need edge access and spacing for a screwdriver
- Pin headers are compact and low profile when needed
- STEMMA QT / Qwiic connectors are very small
- Large connectors can dominate small module designs
Small sensor modules often use STEMMA QT / Qwiic because a screw terminal would be physically larger than the useful circuit.
Serviceability
Serviceability means how easy it is to install, remove, replace or troubleshoot a connection.
| Service Need | Best Connector Direction | Reason |
|---|---|---|
| Connect loose external wires | Screw terminals | No matching plug is needed, only stripped wire |
| Swap small I2C modules quickly | STEMMA QT / Qwiic | Plug-in cables make module changes easy |
| Experiment on breadboard | Pin headers | Works directly with breadboards and jumpers |
| Permanent cable harness | Keyed or locking connector may be better | Prevents reversed or loose connections |
Miswiring Risk
Loose jumper wires are flexible, but flexibility creates risk. It is easy to shift one wire by one pin or swap power and ground.
- Pin headers with loose jumpers have the highest miswiring risk
- Screw terminals are safer when clearly labeled but still require careful wiring
- STEMMA QT / Qwiic reduces miswiring for compatible I2C connections
- Keyed connectors reduce reversed cable problems
For beginner-friendly kits, reducing possible wiring mistakes is often more important than saving a few cents on connectors.
Voltage and Pinout Compatibility
A connector standard only defines the physical and electrical connection order. It does not guarantee every module is voltage-compatible.
- Check whether the I2C bus is 3.3V or 5V
- Check whether the module includes level shifting
- Check whether the power pin should be 3.3V or 5V
- Check whether pull-up resistors are already installed
- Do not assume all 4-pin I2C connectors are safe in every mixed-voltage system
STEMMA QT / Qwiic makes wiring easier, but voltage compatibility still matters.
When to Use Screw Terminals
- External wires connect to the module
- The project uses switches, relays, sensors or field wiring
- Power or higher current must be connected
- Wires should be removable without soldering
- The connection must be mechanically stronger than jumper wires
Screw terminals are the best choice for real wires entering or leaving a project.
When to Use Pin Headers
- The project is on a breadboard
- You are prototyping or experimenting
- You need low-cost flexible connections
- The module plugs into a carrier board or shield
- You want easy test-probe access
Pin headers are the best choice for prototyping, development boards and low-cost module connections.
When to Use STEMMA QT / Qwiic
- The module uses I2C
- You want clean plug-in wiring
- You want to reduce beginner wiring mistakes
- You are building a modular sensor or display system
- The current requirement is low
- The cable stays inside the project or enclosure
STEMMA QT / Qwiic connectors are the best choice for compact plug-and-play I2C module connections.
Choosing by Project Type
| Project Type | Best Connector Choice | Reason |
|---|---|---|
| Breadboard prototype | Pin headers | Easy to connect with jumper wires |
| I2C sensor chain | STEMMA QT / Qwiic | Clean 4-wire plug-in I2C connection |
| Relay output module | Screw terminals for load side | External load wires need stronger connections |
| PLC-style input/output module | Screw terminals for field wiring, headers or I2C connectors for logic side | External wiring and internal module connections have different needs |
| Educational modular kit | STEMMA QT / Qwiic plus clear module labeling | Reduces wiring mistakes and speeds up experiments |
| Power input | Screw terminal or rated power connector | Power connections need current rating and mechanical security |
Common Mistakes
- Using loose jumper wires in a finished project
- Using tiny I2C connectors for loads that need real current
- Assuming all 4-pin I2C cables are voltage-safe in every system
- Forgetting strain relief for external wires
- Using screw terminals where board space and current do not justify them
- Not labeling screw terminals clearly
- Assuming pin headers are mechanically secure enough for moving cables
When to Use Something Else
Sometimes none of these three connector styles is ideal.
- Use locking connectors for cable harnesses that may move or vibrate
- Use JST-style connectors for compact internal power and signal cables
- Use barrel jacks, USB-C or pluggable terminal blocks for power input where appropriate
- Use IDC ribbon cables for many signals between boards
- Use industrial connectors for harsh environments
Conclusion
Screw terminals, pin headers and STEMMA QT / Qwiic connectors all have useful roles, but they serve different project needs.
- Choose screw terminals for external wires, power, switches, relays and field connections.
- Choose pin headers for breadboards, jumper wires, prototypes and development boards.
- Choose STEMMA QT / Qwiic connectors for clean, compact I2C module connections.
A good connector choice makes a project easier to build, safer to use and more reliable over time. The connector should match the electrical load, mechanical stress and experience level of the person assembling the project.