Lighthouse project

You could use the garage door sensor that keep the door from closing is something is blocking. The send a beam from transmitter to receiver and generate a signal when the beam is broken.

Perhaps a copper plate on the floor and another plate 42" above the floor (on the wall). The easiest way to get a complete circuit would be with an old oil-ignition transformer, but you might want to use something low voltage that detects capacitance between the two plates.

Best regards, Spehro Pefhany

Just to be a contrarian...

A wooden sign with a horizontal "Children must be THIS tall to enter" marker is relatively fool-proof.

Additional complexity should take into consideration the liability consequences if Little Johnny gets hurt, Little Johnny is less than 42" tall, and LJ's parents swear that "The light went on saying it was safe for him to climb the stairs."

Not recommending that you not do this but providing an affirmative indicator could mean that you (or the lighthouse foundation or ...) accepts some responsibility, and the device should be designed with that in mind. A "must be THIS tall" sign would seem to leave the responsibility and liability with the accompanying parent/guardian.

Rich makes a great point about liability. However, what if the light simply lit and it's purpose was only implied, without any statements or indications about the significance of the light? Also keep in mind that even if the device worked perfectly, a short kid can still wave his hand and the light will go on. It's a cool idea, and if you do decide to build it, the optical sensor is the obvious solution. If possible, you could add something to entertain the kids not tall enough to go in.

Keep in mind that if a parent brings two kids, and one of them isn't tall enough, they'll probably wait outside and let the other kid run up. So you might also want a sign to tell whether or not parents must accompany kids inside the lighthouse.

Back to the sensor. Do you have access to a power outlet? If not, you'll need a solar cell (probably 5-6 volts), an optional backup power supply (battery and battery charger). 2 diodes to select the power source, an LED, a opto-transistor, another LED. Actually, it's not as simple as it sounds.

MP

I think they have paired devices at radio shack which can send out some signal when the optical path between them is interrupted. You may want to go check out what they have prior to doing any actual electronics design.

If you are not in the US, there must be something like Radio Shack where you live.

--Mac

Why not simply have the lighthouse model exactly 42" high and make sure kids walk in single file between the model and an entry control person. It isn't difficult to tell if a kid is shorter than the top of the model by visual means. That way there is no need to warn anybody or create the impression that liability is implied if kids don't measure up. You simply stop the short kids and steer them to a holding area where they can be otherwise occupied. It also ensures that nobody can pretend they are higher than they actually are by some nefarious method. Electronic methods for such tasks are not foolproof.

I have an idea. Just use a button to turn on the lamp. Put the button up high so that only people over 42" tall can reach it. This makes the circuit extremely simple. Just put a momentary switch in series with the power supply and the lamp. If the lamp is an LED, you'll also need a suitable resistor in series with the LED.

MP

Complete circuit for what? To jolt the kid with 10,000 Volts?

Most likely talking about New York Harbor vicinity:

In article , Franktrem wrote: [....]

Ignoring all the practial issues for a second:

Make the sign a right angle when looked at from above. Both faces are made to look like the lighthouse.

Assume the sign is place so that the measuring side of it faces south and the person is directed to stand with his back against it to be measured.

When the person is not there, the sun light falls on an opening in the model of the lighthouse. This opening could be made to look like a window.

In the "display side" the model has openings where the the glass of the light would be.

Between the opening on the "measuring side" and the "display side" there is a passage lined with aluminum foil. Just behind each opening there is a mirror.

Normally, the light from the bright sky to the south shines in one opening and is directed up to the other. When a person blocks this light, I would be obvious so someone on the east or west facing "display side"

No electronics needed.

Sure. Just put a notice on the sign that says "if your child stands _here_ then starts twitching and drooling he's tall enough!"

Just wire a fluorescent in series to indicate that height > 42". Maybe some additional ballast too so the lamp lifetime isn't compromised.

Best regards, Spehro Pefhany

Mirrors, transient lights source actuated by proximity, and this:

Seriously, one way to do this safely would be to adapt a "stud sensor" (they will detect children as well as engineers). I think they generally "auto-zero" on power-up so that you'd need to turn the power on with nobody nearby (maybe a pressure mat). An SSR could be wired in place of the indicator LED (with due care paid to safety of the line-voltage wiring-- get somebody to do this who knows what they are doing and obey local codes).

Best regards, Spehro Pefhany

Use a high-energy laser and an ordinary smoke detector. If you set the laser 42" off of the ground, it will sear the child's flesh, causing the smoke detector to go off. Children under 42" will not have their flesh seared, and will therefore not set off the smoke detector.

To prevent prolonged searing, you may want to have the smoke detector turn off the laser somehow when it detects smoke.

Yours in jest,

Mac

It's a terrible idea. Have you ever seen a carney? (i.e., traveling circus, but sleazier)? Admittedly, your lighthouse isn't a carney ride, but I think a bunch of electronics to automatically detect a kid's height is lucidrous.

Put the toy lighthouse there, and have your tour guide say, "Kids, I'm sorry, but I'm afraid that you have to be this tall to go upstairs without Mom or Dad holding your hand or carrying you. If you're a toddler and couldn't care less about a lighthouse anyway, there's a play area right over here. :-)" (and include the smiley in the pitch. :-) ) And provide them with some of those oversized Legos. ;-)

Break a Leg! Rich

Just as an idea, but what about mounting a touch plate - 42" + kids arms length, plus allowance for tippy toes, on a wall etc, and only let kids who can reach to touch the plate go up. A touch plate circuit which operates a light and perhaps a recorded message might be fun

David

Franktrem wrote:

Supply stilts for the shorter children.

Very bad idea - that makes it too much like a competition, and the little kids get the short end of the stick.

The way to do it is to have a 42" tall gateway to the toddlers' play area, and say, "You can only go in here if you can fit through this door, otherwise you have to go upstairs with the rest of your family."

;-)

Cheers! Rich