Need 5VDC 100mA to 12VDC 1A converter

... which is probably plugged into an outlet which is likely to be readily stepped down to 12v @ 1a.

But I have a feeling this person knows this, but since they didn't tell us everything about the task at hand all we can do is take shots in the dark.

Hmm, USB,USB..., it smells like some PC hardware is used... I hope it is not controlled by some unstable operating system :-)

What happens if the OS crashes ? All doors are open ? All doors are locked ?

At least make sure that in case of computer or power failure, the people can get out, e.g. in case of fire, using some fully mechanical locking devices.

Paul

Interesting thought. Its a commercial product, though. Ideally, I would like for somebody to just plug the thing into virtually any USB port and let it go to work.

That sure wasn't my intention! The USB spec allows for 100mA, if I am reading it right, unless one has a powered hub. My circutry is all cmos and draws just a few hundred microamps, if that.

Sorry for the late response. I took a few days off of work for the Jewish New Year. Happy New Year everyone. May everything you design, program and/or build work the first time.

I've rec'd parts and have done some experimentation. The solenoid draws

800mA at 12V, 400mA at 6V, and doesn't work reliably at less than 6V. (That seems like a hell of a lot of current for a small, weak solenoid. Whatever.)

No matter how you slice it, that solenoid requires 400mA to run, or damn close to it. Within the constraints of this project, using a cap simply won't work. Keeping the solenoid open long enough for somebody to open the door requires too big of a capacitor, and the recharge time of the cap is too long.

For various reasons, I do not want to put batteries in the product.

Hobby motors also draw a lot of current.

Therefore, I am stuck with a wall wart. I'm not very happy about that, but there's no choice.

In one post, somebody asked whether, in power failure, doors were left locked or unlocked. The answer is locked, but they can still be opened with a key.

Thanks, everyone, for all your feedback.

Mike

Ever been inside of one of those? Do they run on batteries or is there a line goin' to 'em? I don't travel much, but I think the one's I've seen are controlled by a central computer.

RS-422 + power perhaps?

I'd be curious to know what those motors use in terms of power.

Maybe I just have crappy solenoids & should be using something else. My test units pull 400mA after they've been energized.

I didn't create a big setup for measuring the initial surge. I imagine its up there.

Given the need for a wall wart, based on my findings, I will probably end up doing some redesign. But the current inventory needs to go first.

Any recommendations re. solenoids? My requirements are rather loose. Maybe

1/2 pound of force at 10mm. A 5V solenoid with a < 100mA hold current would be great -- I could charge up a cap for the initial surge.

... snip ...

That should be configurable. I worked in one building with such specs, but the problem was the doors lead from the elevator banks to the offices. In case of fire the elevators homed to the basement, the doors were locked, and the stairwells were only accessible from inside the offices, thus cooking anyone waiting for an elevator.

--
 "This is a wonderful answer. It's off-topic, it's incorrect,
  and it doesn't answer the question."  --  Richard Heathfield

 "I support the Red Sox and any team that beats the Yankees"

Hmm... let's see

1/2 pound * g * 10 mm = .250 kg * 10 m/s^2 * 0.01 m = 0.025 Joule =~ 0.021 A * 12 V * 1 s = 0.1 A * 5 V * 0.25 s [Note: your 'pound' may mean something different than I assumed... non-imperial background here. ;-)]

So, at least in terms of pulse energy needed to *move* the pin, that job shouldn't take the amount of energy discussed in here so far to pull open. Not by a factor of 50 or so.

Hold current would be a different issue, of course --- that will be governed by wire resistance, not by mechanical considerations.

So yes, a better solenoid may still get you rid of this problem.

--
Hans-Bernhard Broeker (broeker@physik.rwth-aachen.de)
Even if all the snow were burnt, ashes would remain.

It may be just how you worded it, but that isn't quite what you need to look at.

Connect one of your solenoids to a variable PSU set to 12V, connect up a current meter if the PSU doesn't measure current. Then crank the voltage down and see how low you can get the current before the solenoid drops out.

--
Burn the land and boil the sea,
 You can't take the sky from me.

It drops out, physically, around 330ma, ~5V, but that is below the point of reliability. 6V, 400mA is the min.

Measure that with the solenoid doing its normal job. Then at least double the result for design purposes to ensure a reasonable margin.

--
Chuck F (cbfalconer@yahoo.com) (cbfalconer@worldnet.att.net)
   Available for consulting/temporary embedded and systems.
     USE worldnet address!

That'd be a pretty complicated latch design!

Does anybody know of a good page on solenoid latch designs, such as for door locks and cash drawers? Seeing a few examples would be nice :).

Thanks,

Mike

Also make sure that the nominal solenoid current and voltages are available at least for a few hundred milliseconds or for the worst case mechanical travel time for the lock components. At cold temperatures, the friction can be quite high and thus, decreasing the acceleration and thus increasing the mechanical travel time.

The full magnetic flux should be available until the mechanism reaches the stop. If the flux starts to fall before the stop is reached, it might never reach the stop. If the lock is in some intermediate state when people try to open the door, sooner or later some components of the lock will be damaged.

If the system has been hacked to barely work in warm condition with a well lubricated lock, in cold conditions or when the lock is dirty, it may fail miserably.

Paul

All good points.

One concern of mine is that I am depending on gravity to close the lock rather than a spring. Should things corrode, or get cold, that could be a problem.

Holy Moses! coming up with a good latch design is difficult work!

From what I understand, these devices use a simple controller and a battery pack. They don't use a lot of energy to do their job. The locks just move a tumbler out of the way enough to allow you to open the door. All the real work is done by the patron moving the door handle. The locks I have heard have a method where they don't actually tell the door what the code is from central computer via wire. The locks have a method that stores the current code and the next code for a door. When they hand you a card key, it has your code number and the "next" code number in it. When you insert your card, your current key number should be the next one stored from the last customer, which it moves to the current slot, it then stores the new "next" code from the your card into its memory. The last "current" user got thrown in the bitbucket , which is why the old card will now no longer work. The computer then only has to give the next person a card with the "next " number after you, and another new next number. Then your card's "current" number gets thrown away, and you are locked out. It just rotates through a codes. The computer downstairs just has to handle the "current"/"next" database. If the batteries die in the lock, then they just start the system over with a manager card I guess.

Not that this save you much but, you may want to look into latching type solenoids. These will hold the solenoid down with permanant magnets once you get the thing pulled in all the way, that way you don't have to waste energy on holding the solenoid open. The control of these can get more complicated, I had a nice one with two pairs of coils, one to close, one to open and I could energize either with a darlington transitor. The problem with these in your scenario, of course, would be a failure in open mode when the power fails. You need power to close them.

T.

This isn't universal. I've used video checkout in my room, and it has warned me that after completing the process my key will no longer work. I've tested it. It's true.

True, as with most things in the world, you have your top of the line BMWs and your low end Cheverolets. The style of system I am describing is probably one of the "older" electronic card versions out there. Generally used where you leave the "key" on the nightstand on the way out the door. T.

The "older" systems, huh? Nothin' like a little poke in the side to go with breakfast ;-) As far as I'm concerned, electronic locks are new.

I like the tumbler/handle concept. I can't put it in this product because it sounds like a lot of new drawings and re-tooling, but I'm going to poke around with that when I get some time on the bench.

The lastcode/nextcode concept is interesting. It keeps you from having to run all that wiring.

I remember once when I was on a business trip up north in San Francisco. I was sitting on my bed going through some documents and all the sudden two women unlocked my door with their cards and walked into the room! I know this sounds like the beginning of a Penthouse Forum story, however, they just wanted to know why I was in their room. I called the front desk, etc. IIRC, they fixed the problem with the keys at the front desk before they came out to the room.

Oh well.

This was, maybe, ten years ago. By the time the manager came, all the codes had been re-programmed in the computer.

Mike