Digital Combination Lock!

 

I've always wondered how did electronic locks work, so once i finished the basic digital electronics course I decided to build one myself. And I´ll help you to build your own!

 

You could connect it to anything from 1v to 400v(or maybe more that depends on the RELAY), DC or AC, so you could use it to control another circuit, or even to electrify a fence!! (please dont try that, really dangerous)… I connected a mini chrismas tree to the output (110v) cause I hadnt taken the holydays decoration off my lab, so it was around at the time i finished the proyect.

 

Here are some pictures of the finished System, and a video too, so you can see it working.

Step 1 How does it work?

 

 

First I thought in what was needed to be processed and how. So i drew this diagram as a map to guide me as i build each part of the proyect. Heres a summary of how it works.

• First we need a circuit to decode the 10 possible inputs (0-9) to its 4 output BCD (Binary Coded Decimal), and another output that tells us when any button is pressed.
•  Then we need to build the circuit for our two 7-segments displays to work properly, with 4 inputs for a BCD number and of course 7 outs for our displays, ( I used the IC 74LS47)
• Then a circuit to save each pressed number and toggle between displays
• As well as an internal memory for our password
• And, the hearth of our lock, the comparator (its 8 bits ´cause there are 4 bits per digit in the display, meaning that if you want to do a 4 digit lock you will need two of this connected together.) This will tell us if the numbers in the displays are the same as the password saved in the internal memories.
• And finally a circuit to keep the OPEN or CLOSE signal for an undetermined time, and of course an output (thats whatever you want to control with your lock)

Comments

[Gopesh gopu]

ma chudayo tum

[nikitasamsukha]

nice

[Uranio23]

Hola que tal veo que este proyecto lo hiciste hace tiempo, tengo algunas dudas, me estoy "inspirando" en tu circuito para hacer un proyecto de electronica, no nos dejan usar micro ni nada de eso puras compuertas y cosas basicas.

Me preguntaba si podrias darme mas info sobre el circuito, mi problema esta a la hora de querer hacerlo de 4 numeros la clave, no se como cambiar de memoria cada que pulso un boton... Tu lo haces con el J-K pero como seria para 4 ?

Gracias y espero que puedas responder

[EngineeringShock]

Nice
The LS7220 or LS7222 chips are designed so that you can do the majority of this, minus the displays. I remember when I did this project from scratch. I designed it very similarily.
=)

[Nino123]

yeah, i think that the best part of building something like this {designing everything from scratch} is the excitment of the adventure... having your first design problems, having to do research to solve them, {and probably go nuts for a few days till you get it}...
as i mentioned around the begining, i was trying to use the most basic logic posible, you know, it was when i just completed my first digital electronics course, and most of the IC you could normally order online werent avaliable around here, {thank to Steren, now we got lots of IC and cool stuff cheaper and faster than before}..

anyway, i built it so much time ago... and now i perfectly know how to use uControllers, {PICs}.. so, everything could be controlled from a single chip...
but it was a nice first project...

now i look back at this, and feel a little bit homesick, but proud to have learned so much since then, and willing to keep learning!

ps. thanks for the IC number :D

[djmudslide]

 hey amigo... he intentado tu circuito con un amigo, y tenemos multiples fallas! ...será posible q envies algo de info extra a mi correo? [e-mail]... sobre todo los mapas de conexiones, tengo dudas sobre los puentes q aparecen en el primer mapa, y si existe una sustitucion de los diodos, o cual funcion cumplen (leí como un OR)... gracias d ante mano!

[Nino123]

listo amigo, revisa tu correo electronico, te he enviado una respuesta a tu comentario, si tienes mas dudas, no dudes en contactarme, suerte con el proyecto..

no he subido mas proyectos, por que actualmente estoy dedicandome a aprender mas sobre microcontroladores y PLC...

[3nigmat1c]

It may or may not be interesting, but use of a CD74hc4511 chip will free up a lot of board space (it's a all in one 7-segment to bcd decoder with flip flop and latch).  That way you can support up to 7 displays with a chip per segment and a single 8-3 multiplexer.  That can easily go from 7 to 15 with an additional multiplexer and only need 4 lines for data (always), and 3 lines for addressing (1 extra per new multiplexer). 

Nice project, this was very similar to the Digital Systems final Project I had to do in college.

[AndrewGarza]

 Impressive. I always wanted to make a clock out of low level logic like this. Just seems like a lot of work. It is amazing how much easier/cheaper using a micro controller for something like this.

[amando96]

 indeed, arduino + keypad, + seven segment displays and some code...
thats actually my next project, for a weather station.

[HarveyH44]

Quite an impressive job, both the project and the write up.  The only project I ever attempted like that on a breadboard, was a digital clock, which kept terrible time.  It took months to wire up, and figure out what went wrong.  I've since switched to microcontrollers.  So much easier to debug code, and you can take it anywhere to work on.

Might also look into making PCB at home.  It's not very expensive, and pretty easy with a laser printer.  Although, got a hunch your project would still take sometime to layout, and drilling so many holes...

Really nice work, though don't imagine very many people will build this, maybe a class project.

[Nino123]

thanks, and yeah, i used this as my final proyect in school, you see im currently a 11th grade student here in Acuña, Mexico(Cbtis 54! arriba chivos bravos!)...
so I still dont know how to use microcontrollers (will be seen on 12th), so I used everything i knew so far.
And yeah, microcontroller look really cool, so cant wait to try them!!
which one will be the best for a beginner like me?, PIC, AUDRINO, AVR?...

[ElmoRoyD]

Saludos desde Monterrey, yo soy de Sabinas y estudie en el CBTIS 20 hace ya rato. Es bueno ver gente de la región entrando a estas cosas

[Nino123]

claro que si amigo, yo tambien estaba arto de ver muy pocos trabajos echos por compañeros mexicanos, y pense "pues no keda otra mas que poner manos a la obra" y asi fue coomo empeze, ultimamente he estado algo ocupado por eso no he podido seguir pero pronto continuare con los proyectos...

[thatoneguydavid]

i would suggest Cypress Semiconductor PSoC -3   (programmable system on chip)  with a little practice writing C you can implement really complex systems with very few external components.  they take an FPGA and various analog circuits and wrap them up with a microprocessor on one chip.

[drhoff]

 I agree with Luminous. Arduino is really great for beginners. If you can make a project like this, then you will have no trouble with it at all. Great Instructible.

[LuminousObject]

For a beginner, I would definitely suggest Arduino. You just plug it into the computer and go. No need for any fancy programmers or any of that. Just a USB port and a cable.

[awsomehighvoltage]

why is there a white led there in the middle?

[Nino123]

oh, that led!.. dont worry its not important at all...
I just connected it in the same spot as the first display clock, so i can always know wich is the next digit, (the first or second display), its just a visual aid to so i wont loose track of where the next number will appear, but it doesnt affect or improves the sistem

[peblairman]

Great job! Not trying to flame it or anything, but it looks kinda like a bomb lol

[Udon]

This is really good! It's a lot of info to put together.

I'm starting a Digital Electronics course in Feb. so I'd love to try build this.