In an age where electronic security systems are everywhere—from corporate offices to private homes—custom-built solutions still hold a unique charm and practical appeal. Whether you’re a hobbyist, a tinkerer, or someone simply interested in a more tailored security approach, building your own access control system offers not only security but a deep sense of accomplishment.

In this DIY electronics project, we focus on using the PAL12L6NC, a programmable array logic (PAL) chip, as the central logic component in a custom Security Access Panel. Rather than creating a generalized guide, this article follows a specific project to develop a working access panel that can control a door, gate, or any electronic lock, based on a combination input.

The PAL12L6NC is the brain of the logic decision-making in this build—responsible for verifying input combinations and triggering the lock mechanism only under valid conditions. This project involves no code, no software, and no complex microcontrollers—just pure digital logic using classic programmable logic hardware.

What Makes the PAL12L6NC Special?

The PAL12L6NC is a programmable logic device that dates back to a time when microcontrollers weren’t as prevalent in every corner of electronics. This chip is a compact way to define custom logic circuits without needing dozens of discrete logic gates. It’s essentially a configurable logic brain that can be set up to recognize specific input conditions and provide output responses accordingly.

Some reasons it’s ideal for this project:

● Compact and efficient digital logic configuration

● Ability to replace multiple traditional logic ICs

● Fast and stable operation

● Reliable performance in security-related applications

Using this component offers a nostalgic yet practical way to implement logic without diving into microcontroller coding or modern embedded systems.

Project Overview: Security Access Panel

The goal of this project is to build a standalone electronic access control panel. The system allows or denies access based on a specific combination of button presses, switches, or signals. When the correct combination is entered, the output signal enables a relay or transistor to unlock a door or activate a secure mechanism.

This device can be installed at:

● A workshop door

● A private cabinet

● A home entrance gate

● A garage

● A secured lab or storage area

All decision-making is handled by the PAL12L6NC chip. Once programmed, it continuously monitors the status of the input switches and only responds when the correct pattern is entered.

Concept Design

The security panel features:

● 4 input switches labeled A, B, C, and D

● A hidden master enable switch inside the housing (for setting or maintenance)

● A PAL12L6NC logic chip to detect correct input combinations

● An output control stage using a transistor or relay to activate an electronic lock

● An optional buzzer or LED indicator for feedback

All the parts are mounted in a wall-mounted, tamper-resistant case with a compact and professional look.

Materials and Components

To complete this build, you’ll need the following:

● PAL12L6NC – The programmable logic chip

● DIP socket – For easy insertion/removal of the PAL

● Pushbutton switches (4–6 units) – For user input

● Toggle switch – Hidden enable/reset switch

● Transistor or relay – For switching power to the lock

● LEDs and resistors – For visual indication

● DC power supply (12V or 5V depending on components)

● Lock mechanism – Such as a solenoid lock or magnetic strike plate

● Project enclosure – Wall-mountable with room for panel and wiring

● Wires, headers, and basic tools – For soldering and assembly

Optional but recommended:

● Small breadboard or PCB

● Programming hardware or pre-programmed PAL

● Decals or laser-printed labels for button panels

Step 1: Define Your Security Logic

Before building the circuit, you need to decide what combination of inputs should trigger the "Access Granted" output. For instance, you could define a rule such as:

● Inputs A and C must be pressed

● Inputs B and D must not be pressed

This kind of logic would normally take several discrete gates, but with the PAL12L6NC, it’s condensed into one chip. You can use a hardware programmer to burn this logic into the chip—or have it pre-programmed using software simulation and then order it.

This step is where you make the PAL chip your own. Once the chip is configured to recognize your desired combination, you’re ready to move on to the physical build.

Step 2: Assemble the Input Panel

Mount your input buttons on the front panel of your enclosure. For a clean and professional look, you can use panel-mount momentary pushbuttons.

Label them A, B, C, and D using printed labels or engraving. Route wires from each button to a small header or directly to the breadboard where you’ll plug in your PAL circuit.

Add the master switch inside the case, accessible only when the housing is opened. This can be used for:

● Resetting the system

● Activating programming mode (if needed)

● Temporarily disabling the panel

Make sure all switches are mounted securely and spaced evenly.

Step 3: Building the Logic Circuit

Insert the PAL12L6NC into a DIP socket on your breadboard or PCB. Connect the input switches to the respective input pins of the PAL. The outputs of the PAL will go to an LED and to a transistor circuit that energizes the locking mechanism.

Wire as follows:

● Inputs from switches A-D to PAL input pins

● PAL output pin to the base of a switching transistor (via a current-limiting resistor)

● Collector of transistor to one side of the relay or lock

● Emitter to ground

● Lock connected to external power supply and controlled through the relay

Also include:

● A flyback diode across the relay coil to prevent voltage spikes

● A test LED across the lock output for visual feedback during testing

This setup ensures that when the correct combination is entered, the PAL will activate the transistor, which in turn activates the relay, unlocking the door or mechanism.

Step 4: Power Supply and Safety

The system is powered by a 12V DC adapter. A voltage regulator can be added if you need 5V logic for some components. Ensure your power supply can deliver enough current for the lock mechanism without dipping in voltage.

Safety tips:

● Include a fuse or PTC to protect against short circuits

● Use proper insulation and heat shrink tubing for all exposed wires

● Mount the power components away from buttons and logic circuits

Step 5: Final Assembly and Testing

Once the logic and switching are working, finalize the assembly:

● Mount everything securely in the enclosure

● Route all wires neatly to prevent tangling

● Close the housing and test the unit thoroughly

Check each of the following:

● Pressing incorrect combinations does not activate the lock

● Pressing the correct combination reliably triggers the unlock output

● Resetting the master switch disables the system

● Feedback LED lights up when the lock is active

If everything works as expected, congratulations! You now have a functioning custom-built security access panel using a vintage but powerful logic chip.

Real-World Applications

This project isn’t just for fun. Here are real-world ways you could use your DIY access panel:

● Secure tool storage in a shared workshop – Only authorized users know the code

● Private study or office door – A subtle way to restrict access

● Garage access system – With additional wireless integration, it could serve as an entry point

● Lab or studio lock – For artists, inventors, or engineers needing private space

● Retro-inspired tech art project – Showcasing the use of legacy tech in modern designs

Upgrades and Customizations

Once your system is up and running, you might consider adding:

● Sound feedback – A buzzer or speaker for audio cues

● Timer circuit – To auto-lock after a few seconds

● Battery backup – To keep the system running during outages

● RFID or keypad inputs – Interfacing other systems to work with the PAL logic

Because the PAL handles pure logic, you can add more inputs or change your logic table with a new chip. That’s the beauty of programmable logic devices—you design the behavior.

Final Thoughts

This project serves as a unique blend of vintage digital technology and modern DIY functionality. While most electronics today rely on microcontrollers and software, building with a PAL12L6NC reconnects us with the roots of digital design—where logic was etched in silicon, not typed in code.

Creating a working security access panel with a programmable logic device shows that innovation doesn’t always require the latest technology. With careful planning, a solid design, and the right components, you can build a system that’s functional, durable, and entirely your own.

In the end, the lock may open with a simple click—but behind that is a custom-built mind, born from your creativity, soldering iron, and one humble PAL chip.