Effector (Actuator) Elements
Actuators accept instructions from controllers and translate those into changes in the real world.
High-side transistor switches
A digital control signal from a Raspberry Pi tends to vary over a very low range of voltages, and at low current, while the things we want to actuate will often want to work from a higher voltage and at a higher current; we need a translator, and one really useful one, called a high-side switch, needs only a few components and can live on a tiny circuit board.
A high-side switch gets triggered on or off by that low-voltage logic level but also connects to a larger positive voltage, so that even where the logic and the thing getting switched might share the same ground, the circuit will turn the higher positive supply voltage that the device on or off. For example, we use this to blink the 12-Volt truck marker lights mounted on the garage ceiling to let you know when to stop as you pull in.
If very different voltage or current levels are involved, a high-side switch can operate an electromechanical relay to switch them.
Think of all the things you normally just turn on and off by flicking a switch or pushing a button: ceiling fans, for example, or cooktop exhaust vents or garage door openers.
The device at the right is an electromechanical relay, a mature technology that comes in all kinds of shapes and sizes with all kinds of capabilities, but for which the fundamentals are always the same: when you provide power to a relay, it uses that power to activate an electromagnet inside (a coil of wire wound around a ferric core) that pulls down an armature to cause groups of contacts to make or break electrical connections.
This close-up view shows the top of the coil, the arm and two button-shaped contacts, and allows us to make an important point.
Relays are inherently reliable as long as those contacts remain effective. The specifications of any relay include both current and Voltage ratings for its contacts. If you overdrive those contacts, they will degrade early and become unreliable. If you under-drive them, meaning if they are specified to be able to handle far more current and Voltage than you ever intend to connect to them, they should prove capable of the 40-year endurance that we set for the project. One way to do that, if we feel it is appropriate, is to let one relay drive another when the second has a higher power rating for its contacts.
This is our most complex collection of effectors.
All exterior doors get equipped with Schlage electrified locks.. There is no separate deadbolt and none is necessary. Instead, a spine along the back provides the same kind of stubborn stiffening.
The lock works in a sensible but, to many, unfamiliar way. A 24-Volt solenoid inside determines whether it is locked or unlocked. The inside knob has no hardware; you can always turn it to exit.
The outside knob can always open with a key (this model uses a 6-pin cylinder that's harder to bump, pick or drill open). If the door is not electrically locked, just turn the knob to enter. The key cannot change it from locked to unlocked., but it can always get the door to open.
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