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.

Electromechanical relays

Radio Shack Low-Voltage relayThink 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.

Relay close-upThis 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. 

Fire response

This is our most complex collection of effectors. 

USR 5637 voice modem

CALLING THE FIRE DEPARTMENT: Our local volunteer fire department provides us only one option for reaching them: a phone call. That was once an easier task because of a class of products called voice modems that, in addition to data or fax communications, could dial up for voice communications. (They were popular in automatic calling or automatic answering applications, back in the day). We found one remaining choice, a US Robotics (itself a blast-from-the-past brand) model 5637 voice modem. It can seize a phone line, place the call and repeat a message until the other side hangs up. A Raspberry Pi can tailor the audio that gets played. In addition to giving the nature of the alert (smoke, fire or both) and the address of the house, it can indicate how many people and pets are in the house or if the house is empty.

E Ink Pearl

FLOOR PLAN: We want to make sure that firefighters waste no time getting to where they are most needed and that begins at the front door. The E Ink Pearl digital paper sign in the picture shows you the look of our front door panel but not, of course, the message. This display usually appears to be simply a vanity panel, showing the house number or the family name in big characters, driven by a dedicated Raspberry Pi because it is actually an 800 x 600 graphic display. In the event of a fire, the display changes to show a floor plan of the house with the location of every adult, child, infant or per within the house, as well as the locations of hot spots. A battery within the panel can help it maintain that display even if the power and data feeds from the house are all interrupted.

Triple-plus gas valve

SHUTTING OFF THE GAS:  The natural gas line feeding the house presents a fuel source that it makes sense to deny a fire. There is a main shutoff valve at its entry point, but that requires manual operation, and in any case, we can foresee circumstances where we would not want to cut off gas to the backup power generator, which is the first connection to the gas line after it enters the house (and power is needed for the pump to provide water). A second gas shutoff valve that our automation can shut down gets placed just after the feed to the generator, so nothing else in the house will get any gas. Note that when the house can be restored to normal operations, gas appliances (especially those with pilot lights) may require specific procedures before they can be safely operated; natural gas utilities would rather come out and assist with that than lose a steady customer.

Candle flames in the wind

TURNING OFF FANS and CLOSING OFF AIR FLOW: Fuel and air are companions in combustion so it is as important to deprive a fire of one as it is the other. Instructions to the thermostat to shut down the HVAC (if testing proves it necessary, we can directly deprive the HVAC of power) and signals to shut down all ceiling fans remove replenishment and motion of air inside the house. A command to the Ecovent System to fully close all vent shutters stops the transit of air between rooms.

 

Doors

Deadlatch style door latchAll 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.

Schlage D Series electrified lockThe 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.

Schlage cylinder closeupThe 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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Editorial Project House

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Lot 14, Riding Ridge Court
Builder Don Cerra

 

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