Newbie question – building a locking circuit

I'm a relative beginner to electronics. I have a general understanding of electronics, I can solder, can do Kirchoff's Laws, etc. But I don't have much practical experience with making circuits.

I'm also in the middle of planning to build a house, and I want there to be a really unique lock on the front door. I'm envisioning the lock as a hole with several electrodes in it. The "key" would be a random, non-uniform, irregularly shaped natural semiconductor (for example, a rock or gemstone or something) - something with non-uniform, frequency dependent capacitance and such. The negative electrodes would pump into the "key" a haphazard but consistent pattern of AC at different voltages and frequencies. The positive electrode would be connected to a circuit to measure the current returning through the "key". When programming the lock, the measured values would be recorded in nonvolatile memory. When testing the lock, the measured values would be compared to the recorded values, and if a match (within a reasonable tolerance), the lock would be toggled - locked if unlocked, unlocked if locked.

It doesn't *sound* like something that complicated, but I've never worked on such a project before and honestly don't know where I'd even start. Could you point me to a starting point for what sort of hardware I'd be looking at?

Thanks.

As with so many projects the devil is in the details. Picking a material with varying but consistent (over time, temperature and humidity) electrical characteristics that can be easily measured would be the first thing. You must also find a material that has consistent conduction on it's surface when it touches a probe so you measure the characteristics of the material, not the connection.

I don't know anything about natural materials but I would imagine they'd have high resistances or low capacitance and possibly relatively little variation so the measurement would be difficult. Further the connection might have a big effect.

The mechanical problem as I imagine is that you want to insert a rod or something like it so that the contacts rub along it until it's seated.

Ball plungers are spring loaded balls for detents and might make good contact surfaces without scraping the rod.

The measurement technique depends mostly on the characteristics that you measure, so I'd find a material with measurable and varying characteristics. Then it would be much easier to figure out the measurement scheme.

Once you have a characteristic you can measure there are lots of ways to do it. A high resistance could be brought into an amplifier circuit and read by the analog input to a microprocessor. An RC oscillator using either the keys resistance or capacitance could be feed into a microprocessor counter to determine the value, or ...

First you need a material and have some numbers for it. Good luck on that.

Once you have a good material and a good way to measure it the microprocessor could read the material and save it's characteristics.

You’ve been watching to many films

Come down to reality Think RF ID and magnetic lock Think Bluetooth operated from a mobile phone or think Smart card technology even think network control over solid wire Ethernet keyless solution

Think android applications via wifi or internet control even J2ME

As for electrodes and atomic bombs, cryptonite, etc Mate leave that to the dreamers in the world like Mark Rolph alias "thinks he’s night rider , the Hoffman , dreams it lives it, almost controls his life with it , sick in the head with it " , because unfortunately pal that’s all they are pipe dreams Motorized levers yes possible but to be honest there is no better method at the end of the day than a solid Mortis lock I have asked about motorized locks any idea of the price you will pay


Superman isnt about The world doesent need a saviour and crime isnt solved but the likes of NightRider, Bond 007 or any other silly actor , the goblin fairy princess or the sultana of brown eye , sorry that should have Brunie

Pal don’t even go there !! unless you’re a billionaire which uhm unfortunately most of us aren’t and any way who the hell wants to be a billionaire or a rock star , Disas … star

I cant think of anything worse to be honest loads of little girlies screaming and chasing you round from one place to another shouting, ooooh, oooh, oooh , thrombosis , my hero , setaing like mad , with nickers falling down to thier ankles

They dont last long very limited life and a very hectic terrible life they lead with this

Boring !!! I mean how Boring !!!

Think reality and practical solutions you will make far more money and be a dam site happier

Apart from which I let you into a secret The ones that pay you on time and the ones that are genuine about work etc are not the ones with money with famous titles etc they the worst payers in the country and also the the ones that pull the filthiest tricks They are also most times the ones that cause the most trouble because they behave and act like spoilt little brats and cant stand losing FACT !!! Take it from me I know only to well how some of them carry on

I'm trying to think if you could possibly be any ruder Mark and I'm drawing a blank.

Heaven forbid that a person like functional art.

"Make money"? Did you even read the post?

---

Stephen: I'm mainly concerned about the details of the microprocessor that you mention. What sort of hardware that I could buy could be used suchly? I'm a programmer by trade so I have no issues with learning to program something if necessary.

Hi Karen, and Welcome !
There are many helpful people on this site, and even the few who like throwing buckets of cold water can occasionally be helpful. Just keep your umbrella handy !

It sounds like a wonderful idea to have a totally unique piece of rock crystal or similar for a front door key.
Perhaps you could use a piece of silicon rock, or a conductive gemstone ?

http://en.wikipedia.org/wiki/Silicon

A piezo-electric crystal as used in oscillator circuits has a specific resonant frequency that could easily be tested for.

As Stephen suggests, a microcontroller system could very easily be programmed to read and memorise the characteristic values of an individual rock, and test for them when the key is inserted.

The system would obviously need to be re-programmable in case of loss, but could easily be set up for multiple different keys if required.

The easiest microcontroller system to learn is the "Picaxe", which is designed for hobby and educational use. But as you are a programmer you can take your pic. (Pun intended.)

However, a couple of thoughts that quickly come to my mind:

What if you drop it and chip it, or it gets wet from rain or sweat and that changes its electrical characteristics ?

And of course the problem with a totally unique key to your front door is: what if you lose it ?

(Solution in both cases: you reach in through the cat flap for the secret emergency button.)

But what if someone just steals your key ? So, a secondary sub-system with a keypad for a PIN would be wise.

So maybe a small machined cylinder of natural silicon with an index mark, encased in a protective and decorative acrylic casing, with glorious gold contacts, could be a stylish best seller for your (future) electronic security corporation.

Please don't forget my consultancy fee when you become a billionare !-)

The processor depends a lot on the sensing. If you can amplify the signal to a few volts than most any micro with an analog to digital converter ADC would do what you want. You can use a simple circuit to drive a n-ch mosfet to drive a DC solenoid or use a triac driver and triac (MOC3043 and BTA12-600BW for example) or a relay to drive an AC solenoid.

The software should be fairly simple with the right inputs so most any dumb as dirt micro would do. If you make an oscillator circuit so the frequency varies with the input then any micro with a counter input will do and you don't even need an ADC. Most all micros have multiple counter/timers. You can either count pulses over time or count the interval between pulses depending on the frequency.

This is really a simple application in that you don't care what the values are, so long as they are repeatable and different for different materials.

There are lots of sites that have small control boards with just what you need. They should also have information and tools for programming. I haven't looked in awhile but Adafruit comes to mind.

I often make my own boards for simple controls and I favor the 8051 family and dislike pic processors, but that's just what I'm used to. I suspect the learning curve on assembler isn't worth it but there are lots of micros with software for high level languages. You probably want something fancier than a simple controller, like the 805, so the programming's easier.

If you have more particular information or questions after this link is done I'll be happy to help if you can figure out how to contact me through this site.

- Stephen

I'm not sure the keys will be a big problem with precautions. I'd just have multiple keys with spares somewhere. There's no reason the processor couldn't recognize a few different keys. You probably want some alternative anyway, like an old fashioned lock on a back door with a spare key somewhere in case something fails, like the power.

Thanks for all the comments! I'll check into the Picaxe. And good comments about the backup system - I'd already been thinking about something along those lines.

Obviously dont see the funny side to this or sence of humour If you think im rude you wait till you meet some of these people

Oh boy you dont know what rude is yet are you in for a shock and a half

Rude is rude - it doesn't become nice just because someone else is worse. The "rude" comment was about completely off topic and seemed to be a personal attack on some unrelated third party. I can't see ANY way in which this was funny or relevant.

Soon will Go away and tell what you think after a dew years of working for some of these clowns then you will know what I mean by rude that’s when you’ve grown up a bit and moved around in the industry

Then you can talk to me about rude, seniority included That’s if you last that long if they actually put up with your back chat especially customers You can come back and tell what you think then Try some of your so called pop stars as well when they have lovely little tantrum because you cant fix their equipment or one of your so called flash so called directors or management

That’s what light hearted humor believe you me

Or wait till you get some real nasty peace of work who phones up ypour wife and swears down the phone at her You havent had that yet either have you Or one of you so called stock brokers whos apparently losing god knows how much an hour whilst you attempt to re instate his network connection and your jobs on the line We see what you say then


Or if you really fancy yourself you can go and work for NEC and when you do arrive there having waited three hours to start work and left another job to take that position You can put up with being told verbally not in writing thats there no job for you despite being arranged thats no letter to advise no nothinbg and then lets see what you say to that as well Thats NEC big company that big company didnt even have the decency to let the employment agency know thier had been a change in plans

And whilst thats happening tweetie pi then you can also look forward to the company youve just left whove signed you into an illegal contact of employment attemting to take you to court for some 25 thousand

Only I dont have to lie thats the differnce hard facts on paper in back and white

Or you also havent had the communications experiances yet with comms enviroment me rude nah i dont think so , compared tob the animals your going to have to deal with hmmmm

In fact I can add quite a few tsories to some of this for if you like Frank can suit thier and tell you a bit more cant you frank if you become a billionaire he wont mind putting up with that for free will he

ha ha !!

Good luck Im itching to see what you come back with in a few years time because its even harder now

I realize that this is really no place for personal issues but I can't resist. I have been writing software and installing industrial control systems since 1977 and used some of the first 8-bit micros. I have dealt with difficult work situations. When down time costs are in the thousands of dollars per hour people can go past rude but that is part of the job and really not worth sniveling over. How old do I have to be?

Primary sources for Picaxe chips and info:

In the UK:
Information: rev-ed.co.uk
Supplier: techsupplies.co.uk (= shop for rev-ed)
Technical Support Forum: www.picaxeforum.co.uk

In the US:
http://www.phanderson.com/picaxe/ Supplies both the chips and helpful information.

Congratulations !! someone is thinking at last

What happens when the IC packs up of there is no voltage Oh dear !! Hence mechanical locks are always better than electronics locks and far safer and stronger

Not much point to this is there apart from how do you open the safe if you lose power !! Hence my humour All look very good untill low and behold the electronics pack up

The solonoid freezes or someone trys to force open the lock which bends and siezes the solonoid

Mustn't say anything must we !! After all thats being rude isnt it untill you cant open the bloody door or safe and then your really in trouble

Hence pipe dreams Toys fine realtime advanced security locks if you havent noticed are not electronic They are in fact still mechanical Og blast thats that idea out the window too

I’ve already looked into all of this before spoken to qualified locksmiths who know exactly what they are talking abut and have been in the Industry for years and years and years fitting safes, security locks etc and they always recommend mechanical locks Always !!

I dont say things like this without asking or having been through all of this before I say because i know exactlywhats going to fail first having been a victim of many a breakin both shops and cars etc etc and knowing full well how far people will go to get what they want by force or otherwise I woulld never recommend electronic soloniod locks except for toys or electricla household items and even then like any binary code which is just simply on or off states they can crack that too

Im sorry if this offends you but Ive been in the industry long enough to know full well how this is done watched highly qualified people do thsi for a living They crack security codes !! And they brilliant at it make no mistake BRILLIANT AT IT

Kids toys Yes fine no one worries to much about that

Also if you haven noticed all doors that feature even electromagnetic locks always include a mechanical lock Other wise what happens when you get an electrical power failure OH dear fancy that doors wide open

Hey but why listen to a qualified locksmith after all they don’t have a clue do they?? After all they are silly people who have been in bussiness for years and years because they silly according to some of you

No wonder people make fun of some of you always have to argue dont you !! hmmmm yes Normal I guess



Toodle loo

This may be way out of your box and possibly you don't live in a house that has two doors so it never occurred to you, but all the houses I know of have more than one outside door. This can be useful if a door won't open (electric or not - all things can fail), but it is really useful if the room that contains the door is on fire.

As far as I can see if you were aware of this then your blathering was just a way for you try and belittle people and be self important, which is really rather pathetic.

I have better things to do with my life than sit here arguing If you’ve got something interesting to say and its beneficial then by all means do so but as for games No sorry I don’t have time or the patience for it


You do from here what ever it is you feel you want to do entirely your choice Given you some good advice, up to you, either you take note or make your own mind up

Too many people in the world who will take note unfortunately you always going to have a few that want nothing else but to argue

Id rather listen to professionals who know thier jobs inside out and have been in this game for many many years and are still in bussiness

I dont think they are wrong myself but thats up to you Again your choice

I dont like wasting my time far to many people that I can help and are quite glad and happy to listen to me and Ive known them for many years and they still in bussiness so there we go old chappy

Toodle loo again

Mark,
I'm not sure if you noticed mate but your full stop (period for you yanks) button doesn't seem to be working.

Regards,
James