How To Automate Anything. A Guide to Parts Every Maker Should Know How To Use.
A practical survey of core electrical components needed to add automation to maker/shop projects. Covers DC power supplies, relays/contactors, proximity sensors, limit switches, reed switches, and breakout boards — explaining how each works and when to use it. ---
Key Concepts
| Concept | Definition |
|---|---|
| Relay | An electrically actuated switch that can control one or many other switches; enables computer or sensor control of circuits without physical human input |
| Contactor | The high-power version of a relay; used for large motors and heavy loads |
| Normally Open (NO) | Circuit is open (disconnected) in the relay's default state; closes when coil activates |
| Normally Closed (NC) | Circuit is closed (connected) in the relay's default state; opens when coil activates |
| Poles | Number of independently switchable strips inside a relay (e.g., 2-pole, 4-pole) |
| Double Throw (DT) | Each pole switches between two contacts (one NO, one NC); Single Throw has only one contact per pole |
| NPN vs PNP sensors | NPN = signal line is negative; PNP = signal line is positive (PNP has two P's → two positives, so the signal end is also positive) |
| Breakout board | Adapter that converts microcontroller pins (Arduino, Raspberry Pi, Teensy) into screw terminals for easier, solder-free wiring |
Notes
DC Power Supplies
- Required to power most automation components (relays, microcontrollers, sensors)
- Two categories:
- **Industrial (DIN rail-mounted)**: More durable, typically 24 V, more expensive
- **Hobby/DIY (screw-mount or wall-wart)**: Cheaper, various voltages, good for smaller projects
- Key specs to match:
- **Voltage**: Must match what your components require (e.g., 5 V for Raspberry Pi, 12 V or 24 V for relays)
- **Current (amps)**: Supply must handle the sum of all connected loads
- Some supplies output multiple voltages (e.g., 5 V and 12 V on separate terminals)
- Supplies with wide input voltage ranges may have a physical 115/230 V selector switch — verify before use
- Wall adapters may not label polarity clearly; always verify with a multimeter before connecting
- Industrial supplies have ventilation slots — ensure adequate airflow inside any enclosure
Relays and Contactors
- **Four main reasons to use a relay:**
- Practical example: dust collection automation — relay with a timer keeps dust collector running ~5 seconds after the power tool turns off, no programming needed
- Practical example: motor limit switching — relay reverses or stops a motor when a limit switch is hit
- Practical example: thermal protection — temperature sensor trips relay to cut power before overheating
- Contactors are functionally identical to relays but rated for much higher power; typically single-throw
- Wiring the coil terminals activates the switching mechanism; the load terminals are separate
Proximity Sensors
- Detects presence of metal without physical contact
- Output: a voltage signal (usable to trigger a relay directly if load is within sensor's current limit)
- **Sensing distance matters**: detects steel at a greater distance than aluminum; requires very close proximity for non-ferrous metals
- Advantage over limit switches: no mechanical contact, so no wear or risk of damage from fast-moving parts
- Wiring (3-wire sensor):
- Brown → positive supply
- Blue → negative supply
- Black → signal output
- Spec sheet items to check: supply voltage range, maximum load current (e.g., 300 mA)
- Real project use: CNC table saw blade position detection (up/down end-of-travel)
Limit Switches
- Mechanically actuated switch triggered by physical contact
- Useful for end-of-travel detection on any moving carriage or axis
- **Hysteresis / engagement gap**: engage point and release point are different — can be used intentionally
- Example (CNC homing): first click = stop and reverse; second click (on slow back-off) = precise home position
- Allows fast approach + slow precise home without extra sensors
- Available in multiple form factors: rocker arm, push button, roller (inline or 90°)
- Can be wired NO or NC depending on application logic
Reed Switches
- Tiny glass-enclosed switch closed by proximity of a magnet
- Low current capacity — suited as a signal input to a relay, not a direct load switch
- No moving parts exposed; very small footprint
- Use case: detect presence of a magnet attached to a moving part
Other Sensor Types (Mentioned, Not Demonstrated)
- **Temperature sensors**: open/close a circuit at a set threshold, or provide real-time digital readout on a display
- **Pressure sensors**: detect pressure level in a chamber; can be connected to a display for monitoring (e.g., pneumatic cannon project)
Breakout Boards
- Converts microcontroller I/O pins into screw terminals
- Compatible with Arduino, Raspberry Pi, Teensy, and others
- Available in DIN rail format for panel mounting
- No soldering required; more durable for field wiring
- Not essential, but significantly improves ease of wiring and reconfiguration
Actionable Takeaways
- Before buying any power supply, list every component's voltage and current draw; sum the currents and choose a supply with headroom above that total
- Always verify polarity of unlabeled DC adapters with a multimeter before connecting
- Use a relay with a built-in timer for simple automation (e.g., delayed shutoff) — no microcontroller or programming required
- Choose proximity sensors over limit switches for fast-moving axes where mechanical contact could cause damage
- Wire limit switches for dual-click homing: fast approach on first contact, slow precise home on second contact
- Use reed switches as low-current signal inputs feeding a relay when you need magnet-based detection in a tight space
- Add a breakout board to any microcontroller installation to avoid soldering and simplify future changes
Quotes Worth Keeping
Once I learned how to automate my dust collection system, I felt like I had gained a superpower.
Normal refers to when the coil is off. That's the normal state.
A relay can either disconnect a circuit or connect a circuit.
I prefer proximity sensors over limit switches because there's no contact with a proximity sensor... a proximity sensor will never be damaged.