Monday, February 19, 2018

Seven Metal Detectors

There are things I have had to do that I've only done because my nephews are part of my life. Changing diapers, geocaching, and metal detecting quickly come to mind.

Changing diapers is what it is. The little one does what he has to do, then I do what I have to do. Both jobs done well.

Geocaching is high up my Surely-You-Can-Think-Of Something-Better-To-Do™ Scale.

I like to keep moving, so stopping to clamber through undergrowth, searching for a hidden cache, is not my preferred activity. But when you have little ones bicycling along with you, it's a good way to motivate them to cycle further than they would otherwise choose. Being on a mission distracts them from boredom and imagined tiredness. A distant Dairy Queen also helps.

Near the top of my SYCTOSBTD scale is a grown man with a metal detector.

So today, Presidents Day, it was with these thoughts I set out for the home of my 9 and 10-year-old nephews to work through the mechanics of seven metal detectors with them.

The weather gods were telling me not to go. Apparently they don't particularly appreciate metal detectors either.

As I crawled along the freeway in freezing rain, the road surface became increasingly slick, and the windshield increasingly opaque with ice. I exited and pulled over to let the windshield warm up.

At that point I phoned the boys' mother to let her know I would be turning around. The boys would have to take a (freezing) rain check. I'd risk my life for my nephews, but not for their metal detectors. Besides, they'd asked for metal detectors for Christmas: they'll survive a few more days of anticipation.

I decided to take city streets, but soon I was presented with the first crash.
I was able to stop safely.

At that point, I decided crawling along the freeway might be a little less dangerous, with, hopefully, no sudden stops. Our 1996 Civic does not have anti-lock brakes, and it is a little under-provided in the airbag department. I made it home, unscathed.

As I'm writing this, Twin Cities' freeways are turning from green to red on Google Maps. The seven metal detectors will have to wait for another day.

The 7 Metal Detectors

#1: Mechanical Compass

The compass responds to ferromagnetic material (metal that sufficiently disrupts the earth's magnetic field).

 #2: Cell Phone Compass App

Cellphones contain magnetometers that respond to magnetic fields in three dimensions. I loaded and calibrated a rather effective compass app, Compass Steel 3D, from SimplyWerx.

 #3: Cell Phone Metal Detector App

I loaded Metal Detector from Kurt Radwanski into my cell phone. Again, it uses the magnetometer. It responds pretty well to ferromagnetic materials and has the added benefit I can make it play sci-fi sounds when it detects metal.

#4: A Calculator and an AM Radio

A calculator contains an oscillator that emits a radio frequency that can be picked up in the AM band. Metal modifies a calculator's signal, an AM radio presents the variable signal as a tone.

I've read that solar-powered calculators are not effective, presumably because the oscillator signal cuts out when the solar cell doesn't receive enough light.

#5: The Parts to Build an Oscillator Circuit

The oscillator circuit, with a wire coil, emits a radio signal. Metal modifies the inductance of the coil, and hence the frequency of the oscillator. The AM radio from Metal Detector #4 picks up and presents the signal as sound.

I purchased the parts (pictured at the top of this post, along with the radio) as a kit. I must be honest, this one has me mildly anxious, as it involves a 650°F soldering iron. If the boys are high on sugar, I will insist they stand well back.

#6: A Cheap Metal Detector

I don't like to disappoint the little guys. I bought a "Bounty Hunter Gold Digger Metal Detector" from that they can play with outside. I'll keep it hidden in the car's trunk, so it won't distract the boys from metal detectors #1 through #5.

#7: Two Ziploc Bags, Each Containing $25

As I've already established, I don't like to disappoint the little guys. They're just a year and a few months apart in age, so if one gets an item, the other can become upset if he doesn't get the same item. Sharing is something they are still working on.

I will give each of them a Ziploc bag containing $25, which is less than the cost of a metal detector.

I will tell them they are sharing the metal detectors (including #6), but if they don't want to share, they can pool the money to buy a second Bounty Hunter Gold Digger Metal Detector. I'm hoping, by then, they will be so bored by the idea of metal detecting, they'll do something else with the money.


  1. Doubtful! And, I am glad that you turned around... The boys were not..... They had a good day anyway. We need to find a date....


    1. We'll find a date. I don't like to disappoint them. Besides, it's a joy doing stuff like this with them. I love that they are individuals, each approaching ideas in his own way.