Perhaps a big coil or series of coils like traffic signal sensors use. Of couse that would be hard to implement if the postal carrier is in the lane of traffic when stopped at your box.
Maybe you could place the loop (inductor) in a vertical position and and use a micro-controller such as the BS2 or Propeller or Pic and program it to react as needed. Brainstorming here but maybe a series of coils if the resolution is good enough to determine if the vehicle is stationary. You could also implement multiple types of sensors too.

Doc

 

I have not read all the post so I may be out in left field here.
Why not sense when the mailbox door has been opened and then closed?
This would remove all types of vehicles and weather from the problems.

HTH

It appears that you didn't even read the initial requirements!

He wishes to have his mailbox mounted further away from the road than normal, and only extend the mailbox when the mailperson is present.

 

I have not read all the post so I may be out in left field here.
Why not sense when the mailbox door has been opened and then closed?
This would remove all types of vehicles and weather from the problems.

HTH

You'll need to read a bit more... Sensing that the mailbox door was opened, then closed is only one possible solution for trigering the mailbox to pull away from the curb(don't actually have a curb, just asphalt and grass).

I think the biggest key to success here is 1) knowing that the obstruction is the mail car and 2) the speed at which the box reaches its final position. I'm sure the mail person doesn't want to wait to long for some gadget to position the mailbox. I've seen them pull up and pull away within about 6 seconds so by the time they are ready to stuff the box with advertisements(Hmmm maybe I need to design a junk mail chucker to "bounce" mail out!) maybe only 3 seconds have passed. So waiting for a vehicle that is "in range" and stop moving may not be possible. "In range" is my biggest concern.

I am leaning towards SgtWookie's idea with the Ultrasonic sensor, the Ping))). http://www.parallax.com/Default.aspx?tabid=86 despite my lack of knowledge with programming.

I have some bike chain and gears that I could use to attach to a motor. The mailbox could then be fastened to the chain, all of which could be put in the horizontal support(presure treated 4x4.

 

Perhaps a big coil or series of coils like traffic signal sensors use. Of couse that would be hard to implement if the postal carrier is in the lane of traffic when stopped at your box.
Maybe you could place the loop (inductor) in a vertical position and and use a micro-controller such as the BS2 or Propeller or Pic and program it to react as needed. Brainstorming here but maybe a series of coils if the resolution is good enough to determine if the vehicle is stationary. You could also implement multiple types of sensors too.

Doc

I briefly thought about a current loop in the roadbed, but his City/County would object to him damaging the roadway, and perhaps sue him for repairs as well as arresting him for damaging City/County property.

Putting the loop in a vertical orientation would:
1. leave it exposed to the elements and vulnerable to damage
2. be too far from the vehicle to reliably detect it (remember, non-ferrous body panels)
3. if moved closer to the roadway, it would detect the vehicle better, but would likely be damaged/destroyed within a few days due to plows, etc.

THe initial statements were the objection to the cost of sensors he'd found. Since cost is obviously an issue, adding additional sensors, and thus increasing associated costs and complexity of the circuitry, would not likely be seriously considered.

 

Darn......

As much as I like the idea of the "Ping)))" Ultrasonic device I am not so certain that it will work. The Data Sheet reveals that "It is not rated for outdoor use or continual use in a wet environment. Condensation on its transducers may affect performance and lifespan of the device."
Stated also is the "Operating temperature: 0 – 70° C." (Could get as low as -31C)..."The percent error over the sensor’s operating range of 0 to 70 ° C is significant, in the magnitude of 11 to 12 percent." I'd hate to see what the error would be between 0 and -31C given it is not recommended in such conditions.

What do you think, SgtWookie, is this device a goner?

ADDIONAL PROJECT REQUIREMENTS:
All components must operate to temps as low as -25F, -31C. and must be able to withstand moisture or be protectd from it and still function.

 

I think you will need an industrial sensor and you may research the Sick back ground suppression sensor. There are other companies that make back ground suppression sensors but Sick have always fit my difficult applications.

HTH

 

... I have a wireless device setup now that I converted from a wireless driveway motion sensor to a chime once and Latched LED flasher, but the only problem I am having is that the 9V battery in the motion sensor goes dead after about a week....REALLY DEAD! Funny thing is that's the half of the remote circuit I didn't make changes to.

Since you have had some experience modifying off-the-shelf products you may want to look into the use of an existing PIR motion detector as the sensor portion of your project.

I did a quick check on the Internet and PIR sensors are often used in an outdoor application though -25 degrees Celsius may be a stretch.

You will likely need to make sure that it can be de-sensitized to avoid false triggering but it is an option that I have notice has not yet been discussed. How you mount the PIR motion detector may be the key to success if success is possible.

hgmjr

 

I don't see the % of error being significant; even if it was 50%. What would the mailperson care if the box were 2" or 4" from their window, just as long as they didn't have to stick their arm out very far? Besides, even THAT can be compensated for using an algorithm in a microcontroller, if a temp sensor is also consulted (such as an LM34, LM35, LM134/LM334, LM135/LM335, very easy-to-use devices.)

Yes, it would have to be protected from the elements; in what would basically have to be a hermetically sealed enclosure to preclude the entry of moisture, debris, salt spray and critters (salt spray from plowing the roads; critters have acidic fluids in them, not good for electronics).

Speaking of salt spray, I'm afraid that your bike chain/sprocket idea won't work for very long. I haven't lived up north for quite a few years, but they used to salt the roads to melt the ice, and I strongly suspect they still do that. The salt spray knocked up by the plow will quickly turn your bike chain into a rusted and rigid piece of junk. Instead, you should consider using a V-belt drive. I'd considered toothed belts and sprockets, but those would get easily jammed if foreign material were thrown up on it. A V-belt might too, but the Vee shape of the belt would minimize the chance that anything might land in such a manner as to foul the mechanism.

Power is going to be another issue. How were you planning on powering this contraption? Batteries won't last very long. Solar cells are expensive, and would get covered by snow unless placed at a fairly steep angle. Theft/vandalism might be a problem.

 

Since you have had some experience modifying off-the-shelf products you may want to look into the use of an existing PIR motion detector as the sensor portion of your project.

I did a quick check on the Internet and PIR sensors are often used in an outdoor application though -25 degrees Celsius may be a stretch.

You will likely need to make sure that it can be de-sensitized to avoid false triggering but it is an option that I have notice has not yet been discussed. How you mount the PIR motion detector may be the key to success if success is possible.

hgmjr

Not sure, but can I detect a period of motion with a PIR sensor, such as .5s - 1.5s???

I would have to limit the sensor width a bit and point it down to capture an approximate distance necessary to be sure it is the mail car.

 

I don't see the % of error being significant; even if it was 50%. What would the mail person care if the box were 2" or 4" from their window, just as long as they didn't have to stick their arm out very far? Besides, even THAT can be compensated for using an algorithm in a microcontroller, if a temp sensor is also consulted (such as an LM34, LM35, LM134/LM334, LM135/LM335, very easy-to-use devices.)

The PING))) device has a formula for temperature compensation. If the Temperature (°C) is known, the formula is:
Cair = 331.5 +(0.6× TC)m/s

Yes, it would have to be protected from the elements; in what would basically have to be a hermetically sealed enclosure to preclude the entry of moisture, debris, salt spray and critters (salt spray from plowing the roads; critters have acidic fluids in them, not good for electronics).

Will the Ultrasonic pulses permeate clear materials such as plexiglass, mylar, a plastic bag...?

Speaking of salt spray, I'm afraid that your bike chain/sprocket idea won't work for very long. I haven't lived up north for quite a few years, but they used to salt the roads to melt the ice, and I strongly suspect they still do that. The salt spray knocked up by the plow will quickly turn your bike chain into a rusted and rigid piece of junk. Instead, you should consider using a V-belt drive. I'd considered toothed belts and sprockets, but those would get easily jammed if foreign material were thrown up on it. A V-belt might too, but the Vee shape of the belt would minimize the chance that anything might land in such a manner as to foul the mechanism.

My thought was to contain the motor and drive mechanism inside the 4x4 piece of lumber with a thin slit for connecting the box.

Power is going to be another issue. How were you planning on powering this contraption? Batteries won't last very long. Solar cells are expensive, and would get covered by snow unless placed at a fairly steep angle. Theft/vandalism might be a problem.

I was going to get 120V supply to the box but I may only need the appropriate DC voltage to run the system, hence a transformer in the garage.

 

The PING))) device has a formula for temperature compensation. If the Temperature (°C) is known, the formula is:
Cair = 331.5 +(0.6× TC)m/s

There you are.
The LM35 IC is a precision centigrade temp sensor. Suppy it with ground, Vcc of +4 to +20V, and you can read +2°C to +150°C as 10mv/°C on the output terminal. If you supply a negative voltage across a resistor to the output pin using the supplied formula, you can even read negative temps directly.

Will the Ultrasonic pulses permeate clear materials such as plexiglass, mylar, a plastic bag...?

High-frequency sound waves are easily absorbed. Plexiglass wouldn't work. Thin mylar sheeting (about a mil thick) would. Plastic bag wouldn't last.

My thought was to contain the motor and drive mechanism inside the 4x4 piece of lumber with a thin slit for connecting the box.

Wood will absorb the salt and moisture, and will change dimensions on you. PT wood would be better, but it has to cure for several months before you can do anything with it, or it'll turn into corkscrews.

I was going to get 120V supply to the box but I may only need the appropriate DC voltage to run the system, hence a transformer in the garage.

I like a 12V transformer in the garage scenario. You could leave it unregulated low-voltage AC from the garage to the mailbox, and have a regulator circuit at the mailbox. You wouldn't have to bury the wire very deep. For 120VAC, you would have to go down at least 1 1/2 feet, or more depending upon your state regulations - and you'd have to have a licensed electrician install it, with permits, etc. Otherwise, if there were a fire, your home insurance could rightfully balk on paying for the damage repairs - even if your wiring job wasn't at fault.

Even though you'll be running low voltage, you might as well use wire rated for buried 240V operation; the insulation is designed to last and be safe when buried underground.

 

There you are.
The LM35 IC is a precision centigrade temp sensor. Suppy it with ground, Vcc of +4 to +20V, and you can read +2°C to +150°C as 10mv/°C on the output terminal. If you supply a negative voltage across a resistor to the output pin using the supplied formula, you can even read negative temps directly.
High-frequency sound waves are easily absorbed. Plexiglass wouldn't work. Thin mylar sheeting (about a mil thick) would. Plastic bag wouldn't last.

I even have the LM35 sensor on hand.

Wood will absorb the salt and moisture, and will change dimensions on you. PT wood would be better, but it has to cure for several months before you can do anything with it, or it'll turn into corkscrews.

PS wood was what I had intended and proably already have a piece too. The Gear mechanism is not set in stone yet but I do have the parts to make it work, could use a spring adjust to maintain tension.

Otherwise, if there were a fire, your home insurance could rightfully balk on paying for the damage repairs - even if your wiring job wasn't at fault.

Done too much of my own wireing myself for that to matter now. The burried 240V line was what I was thinking of too.

 

Greetings ionic,

Have you considered using multiple IR leds pulsed from a common driver? With a sufficient number of IR leds you could achieve the light source intensity needed to be able to make it possible to detect the reflected light energy from a nearby vehicle. I mentioned pulsing because that will mean that the detector can be setup to look for the pulses allowing it to be less sensitive to ambient sunlight. You will probably need to aperture the detector to provide greater directional sensitivity. You may even need to use some neutral-density filter material to attenuate any unwanted ambient light.

Just another idea to mull over in addition to your ultrasonic approach.

A fascinating project you have here. I do hope you are able to put something together and then report back to us with an attached mpeg or avi movie-clip of the final product.

hgmjr

 

A fascinating project you have here. I do hope you are able to put something together and then report back to us with an attached mpeg or avi movie-clip of the final product.

hgmjr

It will be a community effort, myself as the editor/assembler/tester. The brainstorming and all important detains....such as device selection and programming ideas will be member owned. I am hoping for MUCH support with the programming for all this as I am without the know-how. My friend, although not very good with programming yet, does have a microchip programmer.

If we stick together I will follow through with this as I fear that my idea(s) are
fruitless without member support.

Thanks for your input!

iONic

 

I fear that this project idea is loosing viability. The more and more I see the mail person drop off mail the more I believe the timing aspect will not be workable.
Given a shout 1 sec time for determining that what the sensor see is the mail car there is literally ofter 3 seconds before the driver is pulling away. In other words by time the mailbox is deciding to move, the mail person already would have mail in his/her hand and is ready to open the mailbox. They sometimes have the mail in hand and arm out the window before coming to a stop.

I do believe I will have to can this project now before I spend any money.

I do want to thank all of you for the ideas, criticism...etc. It would have been fun working on it.

Brian