Nuts & Volts - September 2005

Q&A

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Figure 4

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Puzzle Box

that there is always a sequence to the bulbs.

That is, the first switch ^{L4 L3 L2 L1}closed always lights bulb #1, no matter what color it is. The ^2N3904next switch closure

lights bulb #2. The pattern of switch closure isn’t the key, but the order in which the lamps are lighted. Any switch closure can light the next bulb in the sequence. With that in mind, I decided a 4017 would create the ripple effect desired. All that’s needed is a single

pulse for each switch closure. Figure 4 is what I came up with.

The 555 timer generates a pulse each time pin 2 (trigger) goes low — which happens when any of the four switches are closed. The diodes are necessary to prevent interaction between the switches (i.e., a closed switch preventing the negative pulse on the trigger). This pulse advances the 4017 output by one, and lights the corresponding bulb.

Now for the reset. You can either reset the counter by turning it off/on, press a reset button, or have the 4017 do it for you (automatic). The latter two options are shown in Figure 5.

John Responds: Heyyyyy ....... IT WORKS !! It was fun and educational. I am enclosing a picture of my puzzle box (Figure 6), which was made almost entirely with parts from RadioShack.

The order of switch closure can be random. The first switch closed will light L1, the second closure turns off L1 and lights L2, the third turns off L2 and lights L3, and the last turns off L3 and lights L4. Opening any switch has no effect on the lighting order.

gathers the entire bandwidth for processing.

FYI, the sidebands vary in amplitude in a pattern that can be expressed mathematically by Bessel functions of the first kind (Figure 3), where N is the order (carrier N = 0, first sideband N = l, second N = 2, and so forth) of the Bessel function. The modulation index (mf) is 2.5.

Magic Box

Q. I recently saw a fascinating little “black box” puzzle that you might help me solve. It’s a wooden “cigar” box with four colored bulbs in four sockets and four toggle switches. The toggle switches have removable covers on their handles that match the colors of the bulbs. If you flip the green switch, the green bulb lights,

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the red switch turns on the red bulb, and so forth for the yellow and blue. Now, the interesting part of the puzzle is that if you unscrew the bulbs and move them to different sockets, the colored switches STILL control the corresponding colored bulbs.

To further confuse the observer, if you remove the colored covers on the handles of the switches and swap them around, you find that the newly colored switches STILL control the bulb that matches their color, even though you’ve done nothing but swap the plastic sleeves over the handles!

All I know about this circuit is that it uses at least one IC, and a couple of flashlight batteries. To my best knowledge, there are no magnetic switches or other hidden devices. It is all done with logic. I would love to build this puzzle box and I hope you can show me how.

John Seibels Columbia, SC

Figure 5

Magic Wand

Reset

A. This was a new one to me, but once I saw the pattern, it became simple. You told me

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E l e c t r o n i c s

NUTS & VOLTS E v e r y t h i n g

4017 Q5-9 Q9 Q8 Q7 Q6 Q5 CP1 Q4

CP0 Q3 Q2

MR Q1 Q0

4017 Q5-9 Q9 Q8 Q7 Q6 Q5 CP1 Q4

CP0 Q3 Q2

MR Q1 Q0

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Q. How complicated would it be to make an inductive probe for car circuits? I’m interested in monitoring a solenoid that’s only active at highway speeds; a simple LED on/off indicator is all I need. I really don’t want to tap into the circuit, because it requires poking a wire into the connector or cutting the insulation. Doug Arndt