EnergySmart School Inventors

EnergySmart School Inventors

The Plugger

Initial Sketches

Date: Fri, 15 Dec 2000 13:49:28 -0800
To: The Team
Subject: The Plugger Energy Monitoring Device

Fellow 'Pluggers':

Here's a proposed schematic of the system.

basic    more detailed    detailed    refined [download]

The digital wattmeter has a display on the front panel which displays power consumption up to 1999 W. It has a 4-20 mA analog signal output that represents the power. It is in stock at Newark Electronics. This signal is converted to a voltage by passing through the 100-ohm load resistor and this is fed to a process-control comparator. (Dennis to provide details). The second input of the comparator is a voltage derived from turning a potentiometer knob with a pointer against a paper scale. Part of the kids' activity will be to empirically calibrate the knob by setting up a certain power consumption (see below) and then setting the knob level for triggering. The comparator has a relay-closure output which is used to trigger a Radio-Shack-type "Wireless Doorbell". The transmitter end of this is activated by the doorbell button i.e. the relay contacts. The receiver end can be plugged in anywhere in your house, it activates a 'ding-dong'. We can add red and green LED's to this to indicate 'below' and 'above' threshold i.e. wireless doorbell 'unactivated' versus 'triggered'.

Power is fed into the wattmeter by a cable to a standard plug to go into a wall outlet. The output of the wattmeter goes to an outlet strip. We plug in a variety of typical household loads e.g. incandescent lamps, CFL lamps, hairdryers, irons etc. As we plug them in, we take note of the power consumption on the wattmeter. We set a threshold with the knob. Then we plug in something more and — — DING-DONG! — — we get the remote alarm.

The technical aspects are pretty straightforward. But an equally essential part is the presentation: not for US as engineers, but for kids and media types.

Comments? thoughts?


Schematic showing a square box labeled 'Wattmeter' connected to a power strip. To the right is a circular knob and a small rectangular box labeled 'Voltage Comparator'. All of this is located in front of a backdrop.


Hand drawn sketch of the Plugger; Moving clockwise: A variety of appliances, lamps, are plugged into an outlet strip; extending from the outlet strip is a cord ending with a plug; looped over one wire of the cord is a clamp on ammeter (?) with a signal output; this leads to a comparator with relay output; the comparator is linked to 1) a knob indicating setpoint; and 2) a “Radio Shack” remote doorbell transmitter; which, in turn, leads to the final component, a “Radio Shack” remote doorbell.

More Detailed Sketch

Plugger Schematic: The Digital Wattmeter - (Newark 93F6872) with a digital display and proportional output signal - has a 115 VAC line power out to load connection with an outlet stip with numbers of typical domestic loads; lamps, CFL lamps, hairdryer, etc.; the Digital Wattmeter also has a 115 VAC line power in from plug and a 4-20 mA output with a 0.4-2 V signal leading to a Process-control comparator with relay output; the comparator leads to a comparison setpoint (1.8K ohm (for 5 V feed), 1K ohm and 250 ohm); when power consumption exceeds the setpoint a contact closure occurs and a message is sent to the Wireless doorbell transmitter; this, in turn, sens the message to the wireless doorbell receiver, plugged in remotely.


LBNL Engineering renderings by Tony Hansen, Dennis Collins, Rick Diamond, Mark West, Dan Cheng