MakeShift Challenge: High School Lockdown: Most Plausible Entry

David Glass’ Most Plausible Winning Entry
by Lee D. Zlotoff
June 18, 2007

Well, there are a couple of approaches I would take, perhaps dividing the students up into teams to work on each project. This has several advantages. One is that, by using a variety of communications channels, the likelihood of success is improved. Also, it would be difficult for the entire class to participate in a single project. Additionally, by creating teams that are competing against each other, the students may be more motivated to work on the projects.

First, I would construct an Aldis lamp. It should be possible to scavenge one or more of the lights in the shop area to use as an illumination source for the lamp. It should be quite easy to fabricate a mechanical shutter from the available sheet metal and angle iron (although angle aluminum would make for a lighter-weight shutter, which might improve the signaling ease/speed). It may also be possible to build a reflector to increase the amount of light available and to improve the directional characteristics, although one would want a fairly wide beam in order to cover a reasonably wide target area (since one doesn’t necessarily know who may be looking in the direction of the school). The simplest version would be hand-operated, although this would require someone who knew Morse code on both the transmitting and the receiving ends.

It might be possible to use the computer to key the Aldis lamp, although this would require some type of electromechanical actuator (perhaps a motor from one of the machine tools?). This would allow automation of the lamp, which would make it easy to repeatedly send a message (since there is uncertainty whether anyone would happen to be looking in the direction of the school at any particular moment).

A similar approach could be used with a heliograph, if the sun happened to be shining in a window (or an alternative source of high-intensity light was available).

One of the advantages of the Aldis lamp or heliograph approach is that it would be quite easy for someone to signal back (thus establishing a two-way communications channel), perhaps by using a set of Venetian blinds as the shutter for an impromptu Aldis lamp or heliograph.

The second team would use the walkie-talkie, and perhaps the cordless phone, as a second means of communications. Since most walkie-talkies use the 49MHz band, which is shared with a variety of cordless phones and baby monitors, it may be possible to send a voice signal from the walkie-talkie to one of the homes that is equipped with either a cordless phone or a baby monitor. Usually, these devices have a range of less than a quarter of a mile, due to antenna and power limitations, but it would be relatively easy to construct a variety of gain antennas (Yagi-Uda array, corner reflector, phased array), using the materials available in the metal shop.

This would primarily be a one-way communications channel, although there is the possibility that the receiver could be instructed to acknowledge receipt of a message by a visual signaling method, and there is a slight chance that a radio signal could be passed back.

The third team would also work on a gain-type antenna, only this time for the band used by cell phones. Since the local cellular access point is out of service, it may be possible to increase the signal strength enough with a gain antenna to reach an adjacent cellular access point. The gain antenna for this could be of a variety of types, such as the previously mentioned (but differently dimensioned) Yagi-Uda array, corner reflector, or phased array, or even a parabolic dish (since the frequency used by cell phones is significantly higher than the frequency used by the walkie-talkie). It is important that all of the phones be tried using this approach, since different phones may connect with different access points. This approach would result in a bidirectional communications channel.

A fourth team could work on building a gain type of antenna oriented toward increasing the signal strength of the wireless card in the computer so that it could reach an unsecured WiFi access point, either in one of the quarter-mile-distant houses, or perhaps in a local business with WiFi for customers (e.g., coffee shop, motel). This approach would also result in a bidirectional communications channel.

A fifth team could work on the very simplistic approach of writing letters on sheets of paper and taping or holding them up to the row of windows to make a large sign. While there normally wouldn’t be much chance of anyone observing such a sign from a quarter-mile distance, the blinking of the Aldis lamp should attract enough attention (even for people who don’t know Morse code) to look in the direction of the windows, and perhaps read the sign. This would primarily be a one-direction communications channel, although the receiver could be instructed to acknowledge the receipt of a message in a visual manner.

A sixth team could use the metal shop’s arc welder (the metal shop does have an arc welder, doesn’t it?) to form a crude spark (or arc) transmitter. This could be keyed to produce a broad-band Morse code signal which could be received on AM broadcast band radios in homes within a reasonable distance (especially if some of the wire in the shop were fashioned into an antenna connected to the electrodes). This would also be a one-direction communications channel.

—David Glass

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