Nowadays, various electronic locks with electronic keys in the form of a “tablet” or “flash drive” are very popular. The key is a storage device in which a certain digital code is stored. And the basis of the lock is a microcomputer, which reads and analyzes this code.

Two schemes of the simplest combination locks

I will not argue about the advantages and disadvantages of such locks, I simply bring to the attention of readers my development of a similar device operating on an analog principle. The essence of the matter is that in my lock the key is a zener diode for a certain stabilization voltage. If the zener diode in the key matches the stabilization voltage with the zener diode in the lock, the door opens. Moreover, outwardly everything looks as if it is a digital lock with a digital key. Of course, the number of “code combinations” of my lock is disproportionately less than a digital one, but... who knows that you need to select a zener diode?

I can imagine the hysteria of an “advanced” thief trying to guess the digital code to my lock. The diagram of the first version of the lock is shown in. The key is connector X1.1, which is connected to the mating connector X1.2. Ideally, you need to use the housing from the tablet key, such as iButton, and the corresponding connector for connecting it. But you can make any imitation, or use any two-pin connector pair, for example, from audio equipment. The key contains a zener diode, in this case, 8.2V, and a 1N4148 diode connected in series with it.

When connected to connector X1.2, they and resistor R1 form a stabilized source of constant voltage equal to the sum of the zener diode voltage and the forward voltage of the diode. A two-threshold comparator is made on the comparators of the A1 LM339 chip. The reference voltage at its inputs is set by a circuit consisting of resistor R2, two diodes VD4, VD5 and a zener diode, the same as in the switch.

When you connect your own key, a voltage is established on pins 4 and 7 of A1, which is greater than the voltage on the pin by the amount of forward voltage on the 1N4148 diode. 6 A1.2 and the same amount less voltage at the pin. 5 A1.1. Thus, the voltage at pins 4 and 7 of A1 connected together is between the voltages at pins 6 and 5. As a result, the voltage at the direct input of A1.1 will be less than at the inverse input, and at the output, unity. Exactly the same on A1.2, the output is one. The key on transistor VT1 opens and supplies current to relay K1.

Analog electronic combination lock

If the zener diode in the key is not at the same voltage as in the lock, then at least one of the comparators will be at zero at the output, and the voltage at the base of VT1 will not be enough to open it. The peculiarity of the LM339 microcircuit is that its outputs are made according to public key circuits, so they can be connected together, but they must be connected to the power positive with a resistor (R3). Of course, the zener diodes do not have to be 8.2V, they can be for any voltage from zero to 10V, but they must be the same. Capacitor C1 serves to slow down the response to the correct voltage, so that accidental opening does not occur if pulses or some kind of alternating voltage are received at the input. So to speak, protection from accidents.

The diagram of a more complex lock is shown in Figure 2. A key in the form of a flash drive is used here. It is very similar to a flash drive, it has the same USB connector, but instead of a memory chip inside there are only two zener diodes and two diodes. Now the “secrecy” of the castle is twice as great. And all comparators of the LM339 chip are used. There are two zener diodes in the key, they can be the same, they can be different, but it is important that VD2 is the same as VD3, and VD7 is the same as VD11. Relay K1 type KUTS1M, from an old Soviet TV.

This relay has a high-resistance 12V winding, and two closing contact pairs, for a current of up to 2A each at a voltage of 220V. But you can choose an imported analogue, the winding should be 12V and the current should not exceed 30mA. No setup required. It is very important that all the diodes are the same, and the zener diodes in the key are exactly the same as in the lock, and from the same batch.

A combination lock is generally a very convenient and practical thing. With its installation, there is no need to constantly carry a bunch of metal keys in your pocket in order to open this or that shed. To do this, you just need to remember the code.

Combination locks, in general, can be divided into two categories according to their characteristics: mechanical and electronic.

Most electronic combination locks are made on K561TM2, KTZ trigger microcircuits or on microcircuits specialized just for this purpose. Particularly sophisticated designs are appearing these days on microcontrollers and sensors.
First, let's look at the combination lock on the 4017 chip (HEF4017 B.P.). The lock code consists of four numbers pressed in a given sequence. To find the code, you will have to go through 10,000 options.
The proposed scheme (Fig. 1) will help to assemble a simple combination lock with high encryption strength.

Rice. 1. Scheme of a simple combination lock

The diagram shows:

♦ buttonsS6- S9 “correct” code numbers;

♦ buttonsS.I.- S5 digits that are not needed in the code at all.

Initially, there is a logical “1” at pin 3 of the IC.

When the button is pressedS6", logical "1" is supplied to the input of counter 14, and logical "1" appears at pin 2. In the same way, after pressing the "S7" logical "1" appears at output 4, and after pressing the "S8" - output 7.

After pressing the last correct digit "S9" logical "1" appears at output 10. TransistorVT2 opens, the relay is activated and connects the load with its contacts. Relay activation is indicated by an LED.

If you press any of the “wrong” numbers (S.I.- S5) logical “1” will go to pin 15 (“Reset" - reset to its original state), and the selection of the code will have to start all over again. The lock is based on the K561IE9 microcircuit and the KP501A field-effect transistor.

The combination lock circuit (Fig. 2) has few fundamental differences in complexity from the previous circuit.

Rice. 2. Scheme of a simple combination lock with an extended keyboard

The chip is a four-digit Johnson counter. The principle of operation of this circuit is similar to the circuit described above, although there are more buttons on it.

Finally, let’s look at the lock on two K561TM2 microcircuits (Fig. 3).

Rice. 3. Scheme of a simple combination lock on two K561TM2 microcircuits

The electrical circuit works as follows. At the initial moment, when power is applied, the circuitCl, R1 generates a trigger reset pulse (there will be a log “0” at outputs 1 and 13 of microcircuits).

When you press the button of the first digit of the code (in the diagram -S.B.4), at the moment it is released the triggerD1.1 will switch, i.e. at the outputD1/1 log will appear. "1" since at the inputD1/5 is log. "1". When you press the next button, if there is a log at input 0 of the corresponding trigger. “1”, i.e. the previous one worked, then log. “1” will also appear at its output. The last trigger to fireD2.2, and so that the circuit does not remain in this state for a long time, a transistor is usedVT1. It provides a delay in resetting triggers.

The delay is made by charging the capacitor C2 through a resistorR6. For this reason, the outputD2/13 signal log. "1" will be present for no more than 1 second. This time is quite enough for relay K1 or electromagnet to operate. The time, if desired, can easily be made significantly longer by using capacitor C2 of a larger capacity.

To increase resistance to hacking, the number of “unnecessary” buttons can be increased. Up to any quantity - it all depends on your desire and circumstances.

While dialing the code, pressing any wrong digit resets all triggers.

In conclusion, it should be noted that over time, the “necessary” buttons begin to wear out and differ from all the others. So it is advisable to occasionally swap the buttons to ensure even wear.

A combination door lock is a locking device, to open which you need to set or specify the correct combination of numbers. Among them, two main types can be noted - mechanical and electronic. Despite the difference in technology, they have one principle - to open the entrance, you must enter the correct code on the device’s keyboard.

Combination locks for entrances - their advantages and disadvantages

Combination locks for entrances have both advantages and disadvantages over their analogues. The main advantages are:

• no need to make and keep an entrance key with you;
• low cost of the mechanism;
• Losing your key will not prevent you from getting home;
• the presence of backlit keys in electronic and electronic-mechanical devices;
• possibility to change the secret code of the lock.

The most significant disadvantages include:

• the ability to distribute the code among strangers;
• keypads quickly become unusable;
• abrasions on the keys make it possible to select a code for the lock;
• the need to regularly change the code and remember it.

In addition, each type of lock has its own strengths and weaknesses.

Mechanical combination locks for entrances

When the door to the entrance is slammed, the return spring in the mechanical device is charged, the start head is located in the bar, and the latch is retracted. Pressing the correct combination of buttons moves the correct plates, releasing the lock cage. If you release the buttons, the return spring will ensure that the latch returns to its original position.

Despite the simplicity of the device, assembling it with your own hands is quite problematic.

The only way to open a mechanical lock is to enter the correct code, but despite this, the degree of protection is only sufficient to isolate it from bystanders.

The lock can be installed on both right and left doors. To open it from the inside, you just need to pull back the lever. It is recommended to use at least three digits in the code combination.

To recode the lock, you need to remove the screws, spring set and lever. Next, you need to position the levers of the buttons used for the new code at a bevel towards the center of the lock and assemble the device back. You need to check the operation of the lock with the front door open. In winter, VD-40 lubricant should be used on moving parts.

Electronic combination locks

An electronic door lock with a code has a more attractive design, a more convenient procedure for changing and entering a code, as well as a number of various related functions. There are enough parts sold on radio markets that allow you to assemble such a device yourself.

It is advisable to select locks with a digital code according to the following criteria:

• ability to unlock the device with a master card;
• backlighting of the keys;
• weather protection;
• international certificate;
• Possibility of locking different doors using a single key.

The main components from which electronic push-button locks are made:

• The device itself, which includes an electromagnetic drive of the locking mechanism. In order to ensure the mobility of the lock bolt, an electrical impulse must be sent to its electromagnet. This is only possible if the code in the receiver matches the combination on the storage medium. This process occurs on special locks, different from ordinary ones with a bunch of wires coming out.
• An outdoor control panel, which is a reading device that does not include any control electronics. It receives pulses coming from the internal control unit and if the signal code matches, the reader is activated.
• The internal control device, which is the main control center of the electronic lock. It is he who sends an impulse to the electromagnets of the device, ensuring its opening. Most of these locks lock, just like any mechanical slamming device.
• Uninterruptible power supply. It is a necessary component for electronic locks - otherwise, if there is a power outage, it will be impossible to enter the room. Despite the low power of the device, it can ensure the operation of an electric lock for several days. The UPS is a small device located in a hidden place.

Scheme of an electronic combination lock for the entrance - how to assemble it yourself

The combination lock operates on a 4017 chip. This is a multifunctional crystal and now it will also serve as a guard, in the form of an easy-to-manufacture combination lock with a high level of encryption strength. In order to find a code for it, you will have to try 10,000 options, and an incorrectly pressed key does not signal an error in any way. The cipher consists of a combination of four digits entered in a specific sequence. Considered combination lock scheme:

The design of such a device is the same as other electronic locks on microcircuits. Contacts S6-S9 correspond to the numbers that are present in the working code - these are the “necessary” numbers. The keys S1-S5, on the contrary, show numbers that are not included in the code.

• When there is power, there is a voltage on the 3 ms pin, designated logical “1”.
• When the "S6" key is pressed, this voltage appears at the input of the counter "14" and it is triggered, sending the voltage to pin 2.
• The same thing happens after pressing “S7”-“S8” - this sends voltage to pins 4 and 7, respectively.

When the counter records all four correct presses of the code digits, current is supplied to contact number 10, which opens transistor VT2, which supplies power to the relay control circuit. The latter is activated and provides load connection, which is indicated by the LED.

You can assemble an electronic combination lock with your own hands. About this in the video:

Foolproof protection

If, while typing the code, any of the “wrong” buttons (S1-S5) is pressed, voltage is applied to pin 15, which resets the counter, returning the entire circuit to its original position. This is not displayed in any way on the indicators, which makes password guessing much more difficult.

Unauthorized access can be made almost impossible by simply adding a time relay to pin 15, quietly blocking all keys for at least 60 seconds.

In this case, if you enter the code incorrectly, you will have to wait a minute before entering it again. The attacker will not know this, and even if he accidentally guesses the password, it is not a fact that he will type it while the time relay is inactive.

If you know about this feature, then it will take 10-12 thousand minutes to select a password - you will have to continuously enter passwords for about 8 days to select the desired combination. The reliability of such a solution increases almost to its maximum values.

The assembled circuit is only part of the work - now you need to adjust the opening/closing of the lock bolt. To do this, you can either make a magnet or use a ready-made activator, for example a car one.

Using these methods, you need to be aware that in the first case, when there is a power outage, the lock of the front door will automatically open, and in the second case, on the contrary, it will remain closed. Therefore, the second option, equipped with a UPS, is more preferable.

Combination locks have a number of advantages compared to locking devices that are opened using keys. Among them are the absence of a keyhole into which hooligans can stuff various rubbish, the reliability of the mechanism, the absence of the need to carry a key with you at the risk of losing it, and many others.

However, when thinking about purchasing and installing such a lock, many are faced with the problem of the high cost of such locking devices. This prompts good homeowners with straight arms to think about how they can make a combination lock with their own hands. In this article, we will consider the possibilities of manufacturing such locks, their differences from factory production samples, and also study the examples offered by experts for creating a mechanical and electronic locking device.

Is it possible to make an electronic or mechanical combination lock?

Theoretically, if you have the desire and some experience in working with electricity and semiconductor microcircuits, as well as with locking device mechanisms, you can make an electronic or mechanical combination lock. On the Internet you can find many articles and notes that provide diagrams of electronic and mechanical combination locks. However, you need to understand that their quality and reliability will be in question.

Facing problems self-made electronic combination locks, we are forced to admit that most of the schemes proposed in the articles are not functional. As for mechanical locks, some of the proposed options are too complicated to manufacture, while others require factory components, which, however, is not a problem in all cases.

Having studied the topic thoroughly, we came to the conclusion that it is possible to make an electronic or mechanical combination lock yourself. However, if you initially place increased demands on it in terms of performance characteristics, then it is better not to waste time and effort, buy a factory locking device. It is possible that its cost will ultimately recoup the time spent on a fruitless search for a suitable circuit and the efforts to resolder electrical circuits and rework the mechanical elements of the lock. In addition, homemade locking devices have significant differences from factory samples, which we will talk about later.

How will homemade combination locks differ from factory ones?

As mentioned above, homemade combination locks are different from those you can buy in a store. There are many reasons for this, including the use of handicraft techniques when creating individual elements and the dexterity of the person who took up the manufacture of the locking device, and most importantly, the approach that he chose before taking up the work.

By the way, there are two main approaches to making homemade locking devices. The first (and in our opinion the most correct) involves the use of factory parts in the manufacture of an electronic or mechanical lock, so to speak, “in the author’s layout.” And the second approach, which is more risky, involves the handicraft production of individual parts of the locking device and the use of improvised means in the work, so how will homemade locks differ from those that can be bought in a store?

• A homemade combination lock looks aesthetically less attractive than a factory model, although there are exceptions to this rule.
• No one can guarantee the long-term and stable operation of a homemade device. It is possible that at one “wonderful” moment it will stop working, causing you a lot of trouble.
• Code locking devices assembled according to some schemes from the Internet are extremely unreliable. They can be easily opened by selecting numbers, or even more so by pressing all the numbers at once, which does not stand up to criticism.
• Factory coded locks offer simple and intuitive installation. Homemade samples of locking devices are more difficult to install. Sometimes you have to spend a lot of time before you can figure out how to install it correctly.
• Finally, it should be noted that the cost of a factory combination lock includes its installation. The technician will come to you and install the device efficiently without your participation, which will certainly save your effort and time.

Selecting tools and suitable parts

The process of making an electronic or mechanical combination lock yourself is preceded by the selection of suitable parts and tools. In this case, there is no universal set of tools and parts, since their selection will depend on many factors. However, it is quite possible to say exactly what tools and materials you will need. So, to make an electronic or mechanical combination lock, you will need the following parts and tools:

1. ready-made factory microcircuits or parts for their manufacture (board, wires, radio components);
2. soldering iron, tin, rosin;
3. mechanical parts of the lock (levers, bolts, springs);
4. lock body and fasteners;
5. drill, grinder, screwdriver;
6. glue, material for making buttons, etc.

An example of making an electronic combination lock

In our opinion, the most successful microcircuit for a homemade electronic combination lock is considered to be 561L0A7. You can now see its topology, along with the rest of the castle elements, before your eyes. This scheme has a number of advantages over other samples:

• low power consumption;
• the ability to work simultaneously from two power sources, a 12 volt battery and the mains;
• high reliability against hacking, both intellectual and brute.

Low power consumption is ensured by the fact that the entire electrical circuit is de-energized at rest, and in order to connect power you need to press a special button, for example it will be “0”. After pressing the “0” button, you have 15-20 seconds to dial the code and open the lock, after which the circuit is de-energized again. By the way, this scheme uses the SA 1 code panel, which is brought out. To set the code, the SR 1 panel is used, connected to a device for fixing frequencies taken from the radio receiver. It is enough to place the plugs in a special way in the sockets of the device, which will correspond to the 4-digit code.

The circuit protects the lock from intelligent hacking by selection. If the wrong button is pressed while dialing the code, the dialing panel is blocked for 15 seconds, after which the dialing can be repeated. You can increase the blocking time with each incorrect code entry. So, let's take a quick look at the procedure for making an electronic combination lock.

1. We purchase or solder the above microcircuit.
2. We take a plastic box measuring 15x15 cm, cut a hole in it and mount the code panel on it, not forgetting to bring out the wires.
3. We install a microcircuit inside the box and connect it to the code panel.
4. We install a frequency fixation device from the radio receiver on top and connect it to the microcircuit using wires.
5. We cut a hole in the box so as to gain access to the frequency fixation device. We make a plug from a piece of rubber in order to give the device a more aesthetic appearance.
6. We connect the resulting locking mechanism control unit to the battery, which in turn is connected to the mains through the power supply.
7. Using wires, we connect the control unit to the door unlocking drive, which is used in cars with central locking. We, in turn, connect it to a regular latch, which is installed on mechanical locks. You can do without the door unlocking drive and instead connect the control unit to the electric strike. The electronic code lock is ready.

An example of making a mechanical combination lock

A mechanical combination lock consists of several plates (moving and fixed), washers, rivets, bolt guides, deadbolts, a handle for opening the door, springs, stops and cotter pins. The lock structure is shown in the figure. To open the lock, you need to position the handle finger so that the movable plate moves the bolt and opens the lock. There are several such handles and they all interfere with the bolt, unless, of course, they are turned properly. A mechanical combination lock is manufactured in the following order.

• We take three narrow rectangular metal plates, in this case the size and thickness of the metal do not matter much, the main thing is the basic principle of operation. We stack the plates and drill four holes with a diameter of 10 mm each.
• For each hole, you need to select bolts so that they fit in easily, but do not dangle loosely; their heads need to be ground so that they look like rivets.
• The bolt shaft must be processed with a file so that two planes are formed.
• You need to make cuts in the movable bar, this will ensure the mobility of the handle.
• In order for the lock to be opened from the inside, you need to install a special handle for the bolt.
• You need to make marks on the bolt heads to make it easier to type the code.
• We select a suitable housing and begin assembling the lock mechanism.
• We assemble the plates in the sequence shown in the figure, inserting button bolts into the holes. They will need to be brought out by drilling the corresponding holes in the door leaf.
• The movable plates must be spring-loaded to the handle.
• We mount the box with the mechanism on the door using suitable fasteners and check the functionality of the mechanical combination lock.

To summarize, we note that answering the question of how to make a combination lock is far from easy. There are many options and schemes for manufacturing such a locking device. And even if you take a workable scheme, this does not mean that everything will work out for you, because a lot depends on your intelligence, efficiency and experience in the manufacture and installation of locks. Therefore, if you feel that this work is beyond your capabilities, it is better to purchase a good factory lock, in which case the likelihood that it will not let you down is much higher. Good luck with your experiments.

Sometimes chance decides everything. It can push a person to certain actions. Of course, not many people get tired of buying ready-made goods and try to assemble a combination door lock with their own hands. However, a real radio amateur can do this.

Homemade combination lock

Details

An invaluable advantage of such code mechanisms is the fact that almost every radio component is characterized by relatively low cost and versatility. Thus, each part can be replaced with a similar one.

Design

The electronic code lock circuit is quite simple. At the same time, it is durable and is not affected by temperature changes. She is not afraid of either heat or cold. But I would like to emphasize that the instructions for its assembly are also not particularly complicated:

• You just need to purchase the necessary set of radio components, as well as a circuit board;
• Instead of an electronic lock drive, an ordinary electric drive from a car is used;
• The mounts will need to be upgraded, as shown in the following photos and videos. The determining factor here will be the type of lock used for the renovation;

• As for the electric latch, there are two ways to go. Or purchase a ready-made one. Or do it yourself. To do this you will need:
  • Fasten the metal strip to the plastic handle of the lock directly using self-tapping screws;
  • Next, from this plate, attach the spoke that comes complete with the activator to the drive;
  • And then install the electric drive directly on the base of the door, using the same screws.
• The relay board must be installed on the door structure and the wiring must be installed;
• Instead of a housing, a plastic cover is used. You will need to drill two holes in it for subsequent installation;

• The keypad, which will be used in the process of typing the code, is made of a U-shaped aluminum profile. This profile is used in the manufacture of furniture facades, so you can purchase it in every store that sells furniture fittings. The profile will need to be cut based on the number of buttons. Often, such electronic locks have 10 buttons;
• Next, you will need to drill holes for future buttons of the coded product. Moreover, the diameter of the holes should be slightly larger than the diameter of the buttons. In such a way that the button with the cambric put on it can fit into the hole made. Then it will be provided with centering, and therefore freedom of movement when pressed and without jamming. This technology will also ensure that the buttons of a mechanical product do not move as the glue is poured.

Filling buttons

Now the moment has come when you can install the buttons:

• You will need to insert the cambric into the buttons, pre-coat the surfaces with hot glue, and install the structure, as shown in the following photo. This operation must be performed extremely carefully: not a single crack should appear;
• Epoxy is highly fluid, so it can seep into the buttons and simply glue them together. To avoid having to redo all the work, everything should be done carefully;
• To ensure that the buttons are firmly fixed in place, they are pre-glued with two-component glue. It can be purchased at hardware store or in a furniture fittings store, as it is widely used in the process of gluing MDF products;

• Before directly filling the buttons with epoxy resin, all wires must be soldered to them, as well as to the LEDs. This stage is demonstrated in the next photo. Only in this case is a non-separable keyboard and a unique attractive appearance designs. A similar mechanical device is also applicable to security systems;
• Next, you need to drill two holes for the screws with which the panel will be installed on the door;
• In addition, you will need several of the same holes for the LEDs. Their diameter should be 3 mm. The first one has a greenish glow, will be located on the right and will signal the opening of the lock. The second one will remain unused. However, if desired, it can be connected to a power source to continuously backlight the keyboard of a mechanical device. Do not forget that you need to use a white LED, which will direct light to the buttons of the structure.

power unit

Power must be provided by an uninterruptible unit. You can assemble it yourself by following simple instructions. The circuit produces a small continuous current, which is enough to operate several similar devices.

Let's sum it up

Thus, it may be difficult to assemble such a combination lock with your own hands for the first time, but it is a completely feasible task. The instructions described in the article are not particularly complicated. Therefore, if you figure it out and don’t rush, you can assemble an electronic combination lock without having any special skills in the field of radio electronics. Purchase the necessary parts, assemble the mechanism, install it on the door and connect it. In this case, the electronic lock code can be changed if necessary.