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Mystery Cache

Josh's Infrared Cache

A cache by Stan&Ruth Send Message to Owner Message this owner
Hidden : 2/20/2009
1.5 out of 5
1.5 out of 5

Size: Size: regular (regular)

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Geocache Description:

The Geocache is NOT at the posted coordinates. DO NOT go to the posted coordinates! They are for reference only! The cache is one in the series of Josh's Puzzle caches. Some prior preperation will be required before heading out to hunt for this cache. Please read the description carefully. Print the page and bring it with you!

One of Josh’s friends gave their child a small remote controlled airplane for Christmas. Josh asked him “What radio channel was it operating on?” thinking that it was a typical radio controlled model airplane. His friend replied, “I don’t know, I just put the batteries in it and flew it.” He also mentioned that it was to be flown only inside and the remote control had only a range of about 18 feet. Josh said that ”He really had to see that!” When Josh looked at the airplane and the remote control he concluded that it must be using infrared light to control it. He decided that he needed to come up with a method to demonstrate his theory.

Infrared (IR) radiation is electromagnetic radiation whose wavelength is longer than that of visible light (400-700 nm), but shorter than that of terahertz radiation (3-300 µm) and microwaves (~30,000 um). Infrared radiation spans roughly three orders of magnitude (750 nm and 1000 µm).

Infrared Spectrum

Infrared light can be split into three categories:

Near-infrared (near-IR) - Closest to visible light, near-IR has wavelengths that range from 700 to 1300 nm.
Mid-infrared (mid-IR) - Mid-IR has wavelengths ranging from 1300 to 3000 nm. Both near-IR and mid-IR are used by a variety of electronic devices, including remote controls.
Thermal-infrared (thermal-IR or Far-IR) - Occupying the largest part of the infrared spectrum, thermal-IR has wavelengths ranging from 3000 nm to over 30000 nm.

Josh came up with two methods of demonstrating that the remote control was emitting IR.
1. He constructed a simple IR detector from readily available parts. see.
2. He remembered that many digital cameras will also detect IR radiation as well as visible light. Some cell phone cameras will work also. (Top of the line "Smart Phones" such as the iPhone have IR filters for sharper pictures so they will not detect the IR pulses.)

Both methods worked to confirm that the remote control was using IR.

Josh decided that it would be fun to develop a Geocache that would make use of IR in determining the coordinates of the final stage. The first stage contains a small unit that, when a button is pushed, will emit a series of IR pulses at 940 nm. (There is also a small yellow LED that turns on to indicate that the IR pulse emitter is operating). A picture of this unit may be seen here. There are two sets of three series of pulses. The first set are used in the calculation of the final stage’s Latitude and the second set is for the Longitude. For example, if the first set has 3 flashes, 5 flashes, and 2 flashes the offset used in the calculation would be 0.352. Since the flashes are IR radiation, one or the other or both methods are needed to detect the radiation. Modern television remote controls use IR radiation so a TV remote can be used to check out the detection methods to be used.

Finding the Geocache: The first stage is located at the coordinates shown in the Waypoint table. Please copy and print these instructions and bring them along with you Go to the first stage and locate Josh’s IR Pulse emitter. Push the button, and using your chosen IR detection method, count the pulses in each of the 6 series.

Latitude set: _____ _____ ____ Latitude offset: .____________

Longitude set: _____ _____ _____ Longitude offset ._____________

The coordinates of the final stage are found by subtracting the Latitude offset from the Latitude of the coordinates posted for this Geocache (N 42° 07.579 W 083° 21.454) and the Longitude offset is added to Longitude of the Geocache posting.

Final Stage Latitude = ____________ Final Stage Longitude = ____________

The final stage is in a clear plastic 6" x 9" x 2.5" Lock&Lock box.

Please replace both stages carefully so that you can not see the boxes.

This cache is located within Willow Metropark, a part of the Huron-Clinton Metropolitan Authority park system. A Metropark Vehicle Entry Permit is required: Annual Permit $30. Senior (62+) Permit $20. Daily Permit $7.

For General information please call 810-227-2752 or 800-47-PARKS. Or visit our website at

All park rules and regulations apply. Park in parking lots only.

The Hours for Willow Metropark are from 6:00 AM to 10:00 PM.

Dogs, on a leash, are allowed in this park.

Have fun!

The permit for this cache was renewed prior to the 4/15/2017 deadline and again was approved by Kevin Arnold | Southern District Interpretive Services Supervisor Huron-Clinton Metroparks on 04/22/17

Additional Hints (Decrypt)

[Stage 1] Qb abg zbir nalguvat hagvy lbh frr gur benatr fcbg
[Stage 2] Nobhg guerr srrg nobir gur tebhaq

Decryption Key


(letter above equals below, and vice versa)



83 Logged Visits

Found it 71     Didn't find it 2     Write note 5     Temporarily Disable Listing 1     Enable Listing 1     Publish Listing 1     Owner Maintenance 2     

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Current Time:
Last Updated: on 11/15/2017 3:39:07 PM (UTC-08:00) Pacific Time (US & Canada) (11:39 PM GMT)
Rendered From:Unknown
Coordinates are in the WGS84 datum

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