ESP32 + RFID = Smart Access Control in a Simple DIY Build -- Episode 706

e14cstanton — Thu, 19 Mar 2026 11:36:22 GMT

Current Revision posted to Documents by e14cstanton on 3/19/2026 11:36:22 AM

In this project, Mark builds a simple but effective RFID-based access control system using an ESP32 and MFRC522 reader. The system can be programmed to recognise a specific RFID tag and trigger a relay or solenoid lock, making it ideal for securing enclosures, doors, or equipment. The video covers the full process, from circuit design and component selection to firmware setup and real-world installation, including mounting the reader behind glass and integrating a locking mechanism.

Get Locked In and Watch the Project Build

https://youtu.be/8MjzPjKQX1U

Building an RFID-Controlled Lock with ESP32

Mark’s project walks through a complete, working RFID access control system built around an ESP32 and a common MFRC522 reader. It’s positioned as a flexible foundation, something that can open a door, trigger a relay, or secure equipment, and the implementation reflects that balance between simplicity and practical use.

“Once you build it, you can use it to open a mechanical lock or control a relay… whatever you see fit.”

Parts Overview

At its core, the system combines:

An ESP32 as the controller
An MFRC522 RFID reader for tag detection
A relay or solenoid lock for actuation
A transistor + flyback diode to safely drive inductive loads
A push button to enter programming mode

The design is intentionally minimal. As Mark puts it:

“And that’s all there is to it.”

That simplicity is one of the strengths of the project, there’s no unnecessary abstraction, just the essential building blocks required to make a usable access system.

community.element14.com/.../MD_2D00_26-RFID-for-ESP32-Schematic.pdf

Hardware Design Considerations

The circuit reflects a standard embedded control pattern: low-power logic controlling a higher-power actuator.

The transistor acts as a switch, allowing the ESP32 GPIO to control a 12V load.
The flyback diode protects against voltage spikes from the relay or solenoid coil:

“A diode that protects the transistor from the spikes that are generated by the coil.”
The button input enables runtime configuration without reflashing firmware.

Mark also explores different locking mechanisms,from small cabinet latches to larger solenoids, highlighting flexibility in real-world applications. Notably, all examples operate at 12V, which is a practical choice for readily available actuators.

Physical Build and Layout

Rather than staying on a breadboard, Mark moves quickly into a semi-permanent build using perfboard. He physically trims the board to size:

“I use a knife… and I should be able to simply break it.”

This step is easy to overlook but important,it signals a transition from prototype to deployable hardware. The layout decisions (like diagonal placement due to pin pitch) are practical, not aesthetic. This is typical of fast, functional builds.

There are also moments where routing issues appear and are corrected:

“We solve that in a minute.”

That kind of iterative adjustment is realistic and useful for viewers attempting to replicate the project.

Firmware Architecture and Behaviour

The firmware is straightforward but well structured. It uses the MFRC522 library stack and EEPROM for persistence.

Libraries and setup

The project relies on:

MFRC522v2 for RFID communication
SPI for hardware interface
EEPROM for non-volatile storage

Only one external install is required:

“You need to install… RFID MFRC522, version 2.”

Key logic and code breakdown

1. Pin configuration and mode selection

#define relais 14
#define pswitch 12
#define led 2
char programmode=0;

Relay output on GPIO 14
Programming switch on GPIO 12
LED used as a status indicator

At boot, the system checks the button:

if(digitalRead(pswitch)==0){
  programmode=1;
}

This is a simple but effective pattern: boot-time mode selection avoids needing serial commands or UI.

2. RFID detection loop

The main loop exits early if no card is present:

if (!mfrc522.PICC_IsNewCardPresent()) {
  return;
}

This keeps execution efficient and avoids unnecessary processing.

Once a card is detected, its UID is read and converted:

String uidString = "";
for (byte i = 0; i < mfrc522.uid.size; i++) {
  if (mfrc522.uid.uidByte[i] < 0x10) {
    uidString += "0"; 
  }
  uidString += String(mfrc522.uid.uidByte[i], HEX);
}

This conversion step is important, it ensures a consistent string format for comparison.

3. EEPROM storage and comparison

The system uses EEPROM to store a single authorised UID:

EEPROM.writeString(0,uidString);
EEPROM.commit();

And later compares it:

if (uidString == EEPROM.readString(0)){
  digitalWrite(relais, HIGH);
}

Mark summarises the behaviour clearly:

“If there is a match, then it will open the door or activate the relay.”

Design observations, Limitations and Future Improvements

Single UID storage keeps the logic simple but limits scalability
EEPROM use is appropriate for persistence across resets
The 3-second relay activation (delay(3000)) is fixed, this could be parameterised

The final application is a practical one: securing a 3D printer enclosure.

“I do have a curious kid… this way I can prevent her from opening it.”

Mark hints at broader applications but doesn’t extend the design further. There are several obvious next steps:

1. Multiple user support

Currently only one UID is stored. Expanding to a list would make this viable for shared access.

2. Security considerations

UID-based authentication can be cloned on some tags
No encryption or challenge-response mechanism

3. Feedback and UX

Add buzzer or LED patterns for success/failure
Serial output is useful but not user-facing

4. Power and enclosure

No dedicated enclosure or power regulation shown
Long-term installs would need proper housing

This project does exactly what it sets out to do: deliver a working RFID-controlled lock with minimal overhead. It’s approachable, adaptable, and grounded in real use rather than theory.

The combination of ESP32, MFRC522, and a simple transistor driver is well understood—but Mark’s implementation shows how quickly that can become something practical.

“Present my ring… and it will open.”

That direct cause-and-effect is what makes the project useful, and easy to build upon.

Supporting Files and Links

- Episode 706 Resources

Bill of Materials

Product Name	Manufacturer	Quantity	Buy Kit
WURTH ELEKTRONIK Tactile Switch, WS-TATV Series, Top Actuated, Through Hole, Round Button	WURTH ELEKTRONIK	1	Buy Now
Transistor BC517-D74Z	Onsemi	1	Buy Now
Resistor 1K	Multicomp pro	1	Buy Now
Diode 1n4001	Onsemi	1	Buy Now
RFID Tag KW9Z-T1X5B	IDEC	1	Buy Now
Product Name	Manufacturer	Quantity
ESP32 Doit Devkit V1
RFID reader PCB develp. Kit RC522
USB cable and USB power supply
Lock mechanism 5V	BADODO Security	1

Tags: rfid security project, rfid access control system, mfrc522 esp32 tutorial, embedded systems rfid project, rfid door lock diy, esp32 rfid project, solenoid lock control esp32, esp32 relay control, arduino rfid lock, diy electronic lock, esp32 home automation, friday_release, rfid reader esp32 code

ESP32 + RFID = Smart Access Control in a Simple DIY Build -- Episode 706

cstanton — Thu, 19 Mar 2026 11:36:22 GMT

Revision 6 posted to Documents by cstanton on 3/19/2026 11:36:22 AM

Get Locked In and Watch the Project Build

https://youtu.be/8MjzPjKQX1U

Building an RFID-Controlled Lock with ESP32

“Once you build it, you can use it to open a mechanical lock or control a relay… whatever you see fit.”

Parts Overview

At its core, the system combines:

An ESP32 as the controller
An MFRC522 RFID reader for tag detection
A relay or solenoid lock for actuation
A transistor + flyback diode to safely drive inductive loads
A push button to enter programming mode

The design is intentionally minimal. As Mark puts it:

“And that’s all there is to it.”

That simplicity is one of the strengths of the project, there’s no unnecessary abstraction, just the essential building blocks required to make a usable access system.

community.element14.com/.../MD_2D00_26-RFID-for-ESP32-Schematic.pdf

Hardware Design Considerations

The circuit reflects a standard embedded control pattern: low-power logic controlling a higher-power actuator.

The transistor acts as a switch, allowing the ESP32 GPIO to control a 12V load.
The flyback diode protects against voltage spikes from the relay or solenoid coil:

“A diode that protects the transistor from the spikes that are generated by the coil.”
The button input enables runtime configuration without reflashing firmware.

Physical Build and Layout

Rather than staying on a breadboard, Mark moves quickly into a semi-permanent build using perfboard. He physically trims the board to size:

“I use a knife… and I should be able to simply break it.”

There are also moments where routing issues appear and are corrected:

“We solve that in a minute.”

That kind of iterative adjustment is realistic and useful for viewers attempting to replicate the project.

Firmware Architecture and Behaviour

The firmware is straightforward but well structured. It uses the MFRC522 library stack and EEPROM for persistence.

Libraries and setup

The project relies on:

MFRC522v2 for RFID communication
SPI for hardware interface
EEPROM for non-volatile storage

Only one external install is required:

“You need to install… RFID MFRC522, version 2.”

Key logic and code breakdown

1. Pin configuration and mode selection

#define relais 14
#define pswitch 12
#define led 2
char programmode=0;

Relay output on GPIO 14
Programming switch on GPIO 12
LED used as a status indicator

At boot, the system checks the button:

if(digitalRead(pswitch)==0){
  programmode=1;
}

This is a simple but effective pattern: boot-time mode selection avoids needing serial commands or UI.

2. RFID detection loop

The main loop exits early if no card is present:

if (!mfrc522.PICC_IsNewCardPresent()) {
  return;
}

This keeps execution efficient and avoids unnecessary processing.

Once a card is detected, its UID is read and converted:

String uidString = "";
for (byte i = 0; i < mfrc522.uid.size; i++) {
  if (mfrc522.uid.uidByte[i] < 0x10) {
    uidString += "0"; 
  }
  uidString += String(mfrc522.uid.uidByte[i], HEX);
}

This conversion step is important, it ensures a consistent string format for comparison.

3. EEPROM storage and comparison

The system uses EEPROM to store a single authorised UID:

EEPROM.writeString(0,uidString);
EEPROM.commit();

And later compares it:

if (uidString == EEPROM.readString(0)){
  digitalWrite(relais, HIGH);
}

Mark summarises the behaviour clearly:

“If there is a match, then it will open the door or activate the relay.”

Design observations, Limitations and Future Improvements

Single UID storage keeps the logic simple but limits scalability
EEPROM use is appropriate for persistence across resets
The 3-second relay activation (delay(3000)) is fixed, this could be parameterised

The final application is a practical one: securing a 3D printer enclosure.

“I do have a curious kid… this way I can prevent her from opening it.”

Mark hints at broader applications but doesn’t extend the design further. There are several obvious next steps:

1. Multiple user support

Currently only one UID is stored. Expanding to a list would make this viable for shared access.

2. Security considerations

UID-based authentication can be cloned on some tags
No encryption or challenge-response mechanism

3. Feedback and UX

Add buzzer or LED patterns for success/failure
Serial output is useful but not user-facing

4. Power and enclosure

No dedicated enclosure or power regulation shown
Long-term installs would need proper housing

This project does exactly what it sets out to do: deliver a working RFID-controlled lock with minimal overhead. It’s approachable, adaptable, and grounded in real use rather than theory.

The combination of ESP32, MFRC522, and a simple transistor driver is well understood—but Mark’s implementation shows how quickly that can become something practical.

“Present my ring… and it will open.”

That direct cause-and-effect is what makes the project useful, and easy to build upon.

Supporting Files and Links

- Episode 706 Resources

Bill of Materials

Product Name	Manufacturer	Quantity	Buy Kit
WURTH ELEKTRONIK Tactile Switch, WS-TATV Series, Top Actuated, Through Hole, Round Button	WURTH ELEKTRONIK	1	Buy Now
Transistor BC517-D74Z	Onsemi	1	Buy Now
Resistor 1K	Multicomp pro	1	Buy Now
Diode 1n4001	Onsemi	1	Buy Now
RFID Tag KW9Z-T1X5B	IDEC	1	Buy Now
Product Name	Manufacturer	Quantity
ESP32 Doit Devkit V1
RFID reader PCB develp. Kit RC522
USB cable and USB power supply
Lock mechanism 5V	BADODO Security	1

ESP32 + RFID = Smart Access Control in a Simple DIY Build -- Episode 706

cstanton — Wed, 18 Mar 2026 19:12:32 GMT

Revision 5 posted to Documents by cstanton on 3/18/2026 7:12:32 PM

Get Locked In and Watch the Project Build

Building an RFID-Controlled Lock with ESP32

“Once you build it, you can use it to open a mechanical lock or control a relay… whatever you see fit.”

Parts Overview

At its core, the system combines:

An ESP32 as the controller
An MFRC522 RFID reader for tag detection
A relay or solenoid lock for actuation
A transistor + flyback diode to safely drive inductive loads
A push button to enter programming mode

The design is intentionally minimal. As Mark puts it:

“And that’s all there is to it.”

That simplicity is one of the strengths of the project, there’s no unnecessary abstraction, just the essential building blocks required to make a usable access system.

community.element14.com/.../MD_2D00_26-RFID-for-ESP32-Schematic.pdf

Hardware Design Considerations

The circuit reflects a standard embedded control pattern: low-power logic controlling a higher-power actuator.

The transistor acts as a switch, allowing the ESP32 GPIO to control a 12V load.
The flyback diode protects against voltage spikes from the relay or solenoid coil:

“A diode that protects the transistor from the spikes that are generated by the coil.”
The button input enables runtime configuration without reflashing firmware.

Physical Build and Layout

Rather than staying on a breadboard, Mark moves quickly into a semi-permanent build using perfboard. He physically trims the board to size:

“I use a knife… and I should be able to simply break it.”

There are also moments where routing issues appear and are corrected:

“We solve that in a minute.”

That kind of iterative adjustment is realistic and useful for viewers attempting to replicate the project.

Firmware Architecture and Behaviour

The firmware is straightforward but well structured. It uses the MFRC522 library stack and EEPROM for persistence.

Libraries and setup

The project relies on:

MFRC522v2 for RFID communication
SPI for hardware interface
EEPROM for non-volatile storage

Only one external install is required:

“You need to install… RFID MFRC522, version 2.”

Key logic and code breakdown

1. Pin configuration and mode selection

#define relais 14
#define pswitch 12
#define led 2
char programmode=0;

Relay output on GPIO 14
Programming switch on GPIO 12
LED used as a status indicator

At boot, the system checks the button:

if(digitalRead(pswitch)==0){
  programmode=1;
}

This is a simple but effective pattern: boot-time mode selection avoids needing serial commands or UI.

2. RFID detection loop

The main loop exits early if no card is present:

if (!mfrc522.PICC_IsNewCardPresent()) {
  return;
}

This keeps execution efficient and avoids unnecessary processing.

Once a card is detected, its UID is read and converted:

String uidString = "";
for (byte i = 0; i < mfrc522.uid.size; i++) {
  if (mfrc522.uid.uidByte[i] < 0x10) {
    uidString += "0"; 
  }
  uidString += String(mfrc522.uid.uidByte[i], HEX);
}

This conversion step is important, it ensures a consistent string format for comparison.

3. EEPROM storage and comparison

The system uses EEPROM to store a single authorised UID:

EEPROM.writeString(0,uidString);
EEPROM.commit();

And later compares it:

if (uidString == EEPROM.readString(0)){
  digitalWrite(relais, HIGH);
}

Mark summarises the behaviour clearly:

“If there is a match, then it will open the door or activate the relay.”

Design observations, Limitations and Future Improvements

Single UID storage keeps the logic simple but limits scalability
EEPROM use is appropriate for persistence across resets
The 3-second relay activation (delay(3000)) is fixed, this could be parameterised

The final application is a practical one: securing a 3D printer enclosure.

“I do have a curious kid… this way I can prevent her from opening it.”

Mark hints at broader applications but doesn’t extend the design further. There are several obvious next steps:

1. Multiple user support

Currently only one UID is stored. Expanding to a list would make this viable for shared access.

2. Security considerations

UID-based authentication can be cloned on some tags
No encryption or challenge-response mechanism

3. Feedback and UX

Add buzzer or LED patterns for success/failure
Serial output is useful but not user-facing

4. Power and enclosure

No dedicated enclosure or power regulation shown
Long-term installs would need proper housing

This project does exactly what it sets out to do: deliver a working RFID-controlled lock with minimal overhead. It’s approachable, adaptable, and grounded in real use rather than theory.

The combination of ESP32, MFRC522, and a simple transistor driver is well understood—but Mark’s implementation shows how quickly that can become something practical.

“Present my ring… and it will open.”

That direct cause-and-effect is what makes the project useful, and easy to build upon.

Supporting Files and Links

- Episode 706 Resources

Bill of Materials

Product Name	Manufacturer	Quantity	Buy Kit
WURTH ELEKTRONIK Tactile Switch, WS-TATV Series, Top Actuated, Through Hole, Round Button	WURTH ELEKTRONIK	1	Buy Now
Transistor BC517-D74Z	Onsemi	1	Buy Now
Resistor 1K	Multicomp pro	1	Buy Now
Diode 1n4001	Onsemi	1	Buy Now
RFID Tag KW9Z-T1X5B	IDEC	1	Buy Now
Product Name	Manufacturer	Quantity
ESP32 Doit Devkit V1
RFID reader PCB develp. Kit RC522
USB cable and USB power supply
Lock mechanism 5V	BADODO Security	1

ESP32 + RFID = Smart Access Control in a Simple DIY Build -- Episode 706

cstanton — Wed, 18 Mar 2026 19:02:32 GMT

Revision 4 posted to Documents by cstanton on 3/18/2026 7:02:32 PM

Get Locked In and Watch the Project Build

Building an RFID-Controlled Lock with ESP32

“Once you build it, you can use it to open a mechanical lock or control a relay… whatever you see fit.”

Parts Overview

At its core, the system combines:

An ESP32 as the controller
An MFRC522 RFID reader for tag detection
A relay or solenoid lock for actuation
A transistor + flyback diode to safely drive inductive loads
A push button to enter programming mode

The design is intentionally minimal. As Mark puts it:

“And that’s all there is to it.”

That simplicity is one of the strengths of the project, there’s no unnecessary abstraction, just the essential building blocks required to make a usable access system.

community.element14.com/.../MD_2D00_26-RFID-for-ESP32-Schematic.pdf

Hardware Design Considerations

The circuit reflects a standard embedded control pattern: low-power logic controlling a higher-power actuator.

The transistor acts as a switch, allowing the ESP32 GPIO to control a 12V load.
The flyback diode protects against voltage spikes from the relay or solenoid coil:

“A diode that protects the transistor from the spikes that are generated by the coil.”
The button input enables runtime configuration without reflashing firmware.

Physical Build and Layout

Rather than staying on a breadboard, Mark moves quickly into a semi-permanent build using perfboard. He physically trims the board to size:

“I use a knife… and I should be able to simply break it.”

There are also moments where routing issues appear and are corrected:

“We solve that in a minute.”

That kind of iterative adjustment is realistic and useful for viewers attempting to replicate the project.

Firmware Architecture and Behaviour

The firmware is straightforward but well structured. It uses the MFRC522 library stack and EEPROM for persistence.

Libraries and setup

The project relies on:

MFRC522v2 for RFID communication
SPI for hardware interface
EEPROM for non-volatile storage

Only one external install is required:

“You need to install… RFID MFRC522, version 2.”

Key logic and code breakdown

1. Pin configuration and mode selection

#define relais 14
#define pswitch 12
#define led 2
char programmode=0;

Relay output on GPIO 14
Programming switch on GPIO 12
LED used as a status indicator

At boot, the system checks the button:

if(digitalRead(pswitch)==0){
  programmode=1;
}

This is a simple but effective pattern: boot-time mode selection avoids needing serial commands or UI.

2. RFID detection loop

The main loop exits early if no card is present:

if (!mfrc522.PICC_IsNewCardPresent()) {
  return;
}

This keeps execution efficient and avoids unnecessary processing.

Once a card is detected, its UID is read and converted:

String uidString = "";
for (byte i = 0; i < mfrc522.uid.size; i++) {
  if (mfrc522.uid.uidByte[i] < 0x10) {
    uidString += "0"; 
  }
  uidString += String(mfrc522.uid.uidByte[i], HEX);
}

This conversion step is important, it ensures a consistent string format for comparison.

3. EEPROM storage and comparison

The system uses EEPROM to store a single authorised UID:

EEPROM.writeString(0,uidString);
EEPROM.commit();

And later compares it:

if (uidString == EEPROM.readString(0)){
  digitalWrite(relais, HIGH);
}

Mark summarises the behaviour clearly:

“If there is a match, then it will open the door or activate the relay.”

Design observations, Limitations and Future Improvements

Single UID storage keeps the logic simple but limits scalability
EEPROM use is appropriate for persistence across resets
The 3-second relay activation (delay(3000)) is fixed, this could be parameterised

The final application is a practical one: securing a 3D printer enclosure.

“I do have a curious kid… this way I can prevent her from opening it.”

Mark hints at broader applications but doesn’t extend the design further. There are several obvious next steps:

1. Multiple user support

Currently only one UID is stored. Expanding to a list would make this viable for shared access.

2. Security considerations

UID-based authentication can be cloned on some tags
No encryption or challenge-response mechanism

3. Feedback and UX

Add buzzer or LED patterns for success/failure
Serial output is useful but not user-facing

4. Power and enclosure

No dedicated enclosure or power regulation shown
Long-term installs would need proper housing

In Closing

This project does exactly what it sets out to do: deliver a working RFID-controlled lock with minimal overhead. It’s approachable, adaptable, and grounded in real use rather than theory.

The combination of ESP32, MFRC522, and a simple transistor driver is well understood—but Mark’s implementation shows how quickly that can become something practical.

“Present my ring… and it will open.”

That direct cause-and-effect is what makes the project useful, and easy to build upon.

Supporting Files and Links

- Episode 706 Resources

Bill of Materials

Product Name	Manufacturer	Quantity	Buy Kit
WURTH ELEKTRONIK Tactile Switch, WS-TATV Series, Top Actuated, Through Hole, Round Button	WURTH ELEKTRONIK	1	Buy Now
Transistor BC517-D74Z	Onsemi	1	Buy Now
Resistor 1K	Multicomp pro	1	Buy Now
Diode 1n4001	Onsemi	1	Buy Now
RFID Tag KW9Z-T1X5B	IDEC	1	Buy Now
Product Name	Manufacturer	Quantity
ESP32 Doit Devkit V1
RFID reader PCB develp. Kit RC522
USB cable and USB power supply
Lock mechanism 5V	BADODO Security	1

ESP32 + RFID = Smart Access Control in a Simple DIY Build -- Episode 706

cstanton — Wed, 18 Mar 2026 19:00:47 GMT

Revision 3 posted to Documents by cstanton on 3/18/2026 7:00:47 PM

Get Locked In and Watch the Project Build

Building an RFID-Controlled Lock with ESP32

“Once you build it, you can use it to open a mechanical lock or control a relay… whatever you see fit.”

Parts Overview

At its core, the system combines:

An ESP32 as the controller
An MFRC522 RFID reader for tag detection
A relay or solenoid lock for actuation
A transistor + flyback diode to safely drive inductive loads
A push button to enter programming mode

The design is intentionally minimal. As Mark puts it:

“And that’s all there is to it.”

That simplicity is one of the strengths of the project, there’s no unnecessary abstraction, just the essential building blocks required to make a usable access system.

community.element14.com/.../MD_2D00_26-RFID-for-ESP32-Schematic.pdf

Hardware Design Considerations

The circuit reflects a standard embedded control pattern: low-power logic controlling a higher-power actuator.

The transistor acts as a switch, allowing the ESP32 GPIO to control a 12V load.
The flyback diode protects against voltage spikes from the relay or solenoid coil:

“A diode that protects the transistor from the spikes that are generated by the coil.”
The button input enables runtime configuration without reflashing firmware.

Physical Build and Layout

Rather than staying on a breadboard, Mark moves quickly into a semi-permanent build using perfboard. He physically trims the board to size:

“I use a knife… and I should be able to simply break it.”

There are also moments where routing issues appear and are corrected:

“We solve that in a minute.”

That kind of iterative adjustment is realistic and useful for viewers attempting to replicate the project.

Firmware Architecture and Behaviour

The firmware is straightforward but well structured. It uses the MFRC522 library stack and EEPROM for persistence.

Libraries and setup

The project relies on:

MFRC522v2 for RFID communication
SPI for hardware interface
EEPROM for non-volatile storage

Only one external install is required:

“You need to install… RFID MFRC522, version 2.”

Key logic and code breakdown

1. Pin configuration and mode selection

#define relais 14
#define pswitch 12
#define led 2
char programmode=0;

Relay output on GPIO 14
Programming switch on GPIO 12
LED used as a status indicator

At boot, the system checks the button:

if(digitalRead(pswitch)==0){
  programmode=1;
}

This is a simple but effective pattern: boot-time mode selection avoids needing serial commands or UI.

2. RFID detection loop

The main loop exits early if no card is present:

if (!mfrc522.PICC_IsNewCardPresent()) {
  return;
}

This keeps execution efficient and avoids unnecessary processing.

Once a card is detected, its UID is read and converted:

String uidString = "";
for (byte i = 0; i < mfrc522.uid.size; i++) {
  if (mfrc522.uid.uidByte[i] < 0x10) {
    uidString += "0"; 
  }
  uidString += String(mfrc522.uid.uidByte[i], HEX);
}

This conversion step is important, it ensures a consistent string format for comparison.

3. EEPROM storage and comparison

The system uses EEPROM to store a single authorised UID:

EEPROM.writeString(0,uidString);
EEPROM.commit();

And later compares it:

if (uidString == EEPROM.readString(0)){
  digitalWrite(relais, HIGH);
}

Mark summarises the behaviour clearly:

“If there is a match, then it will open the door or activate the relay.”

Design observations, Limitations and Future Improvements

Single UID storage keeps the logic simple but limits scalability
EEPROM use is appropriate for persistence across resets
The 3-second relay activation (delay(3000)) is fixed, this could be parameterised

The final application is a practical one: securing a 3D printer enclosure.

“I do have a curious kid… this way I can prevent her from opening it.”

Mark hints at broader applications but doesn’t extend the design further. There are several obvious next steps:

1. Multiple user support

Currently only one UID is stored. Expanding to a list would make this viable for shared access.

2. Security considerations

UID-based authentication can be cloned on some tags
No encryption or challenge-response mechanism

3. Feedback and UX

Add buzzer or LED patterns for success/failure
Serial output is useful but not user-facing

4. Power and enclosure

No dedicated enclosure or power regulation shown
Long-term installs would need proper housing

In Closing

This project does exactly what it sets out to do: deliver a working RFID-controlled lock with minimal overhead. It’s approachable, adaptable, and grounded in real use rather than theory.

The combination of ESP32, MFRC522, and a simple transistor driver is well understood—but Mark’s implementation shows how quickly that can become something practical.

“Present my ring… and it will open.”

That direct cause-and-effect is what makes the project useful, and easy to build upon.

Supporting Files and Links

Bill of Materials

Product Name	Manufacturer	Quantity	Buy Kit
WURTH ELEKTRONIK Tactile Switch, WS-TATV Series, Top Actuated, Through Hole, Round Button	WURTH ELEKTRONIK	1	Buy Now
Transistor BC517-D74Z	Onsemi	1	Buy Now
Resistor 1K	Multicomp pro	1	Buy Now
Diode 1n4001	Onsemi	1	Buy Now
RFID Tag KW9Z-T1X5B	IDEC	1	Buy Now
Product Name	Manufacturer	Quantity
ESP32 Doit Devkit V1
RFID reader PCB develp. Kit RC522
USB cable and USB power supply
Lock mechanism 5V	BADODO Security	1

ESP32 + RFID = Smart Access Control in a Simple DIY Build -- Episode 706

cstanton — Wed, 18 Mar 2026 18:58:04 GMT

Revision 2 posted to Documents by cstanton on 3/18/2026 6:58:04 PM

Get Locked In and Watch the Project Build

Building an RFID-Controlled Lock with ESP32

“Once you build it, you can use it to open a mechanical lock or control a relay… whatever you see fit.”

Parts Overview

At its core, the system combines:

An ESP32 as the controller
An MFRC522 RFID reader for tag detection
A relay or solenoid lock for actuation
A transistor + flyback diode to safely drive inductive loads
A push button to enter programming mode

The design is intentionally minimal. As Mark puts it:

“And that’s all there is to it.”

That simplicity is one of the strengths of the project, there’s no unnecessary abstraction, just the essential building blocks required to make a usable access system.

community.element14.com/.../MD_2D00_26-RFID-for-ESP32-Schematic.pdf

Hardware Design Considerations

The circuit reflects a standard embedded control pattern: low-power logic controlling a higher-power actuator.

The transistor acts as a switch, allowing the ESP32 GPIO to control a 12V load.
The flyback diode protects against voltage spikes from the relay or solenoid coil:

“A diode that protects the transistor from the spikes that are generated by the coil.”
The button input enables runtime configuration without reflashing firmware.

Physical Build and Layout

Rather than staying on a breadboard, Mark moves quickly into a semi-permanent build using perfboard. He physically trims the board to size:

“I use a knife… and I should be able to simply break it.”

There are also moments where routing issues appear and are corrected:

“We solve that in a minute.”

That kind of iterative adjustment is realistic and useful for viewers attempting to replicate the project.

Firmware Architecture and Behaviour

The firmware is straightforward but well structured. It uses the MFRC522 library stack and EEPROM for persistence.

Libraries and setup

The project relies on:

MFRC522v2 for RFID communication
SPI for hardware interface
EEPROM for non-volatile storage

Only one external install is required:

“You need to install… RFID MFRC522, version 2.”

Key logic and code breakdown

1. Pin configuration and mode selection

#define relais 14
#define pswitch 12
#define led 2
char programmode=0;

Relay output on GPIO 14
Programming switch on GPIO 12
LED used as a status indicator

At boot, the system checks the button:

if(digitalRead(pswitch)==0){
  programmode=1;
}

This is a simple but effective pattern: boot-time mode selection avoids needing serial commands or UI.

2. RFID detection loop

The main loop exits early if no card is present:

if (!mfrc522.PICC_IsNewCardPresent()) {
  return;
}

This keeps execution efficient and avoids unnecessary processing.

Once a card is detected, its UID is read and converted:

String uidString = "";
for (byte i = 0; i < mfrc522.uid.size; i++) {
  if (mfrc522.uid.uidByte[i] < 0x10) {
    uidString += "0"; 
  }
  uidString += String(mfrc522.uid.uidByte[i], HEX);
}

This conversion step is important, it ensures a consistent string format for comparison.

3. EEPROM storage and comparison

The system uses EEPROM to store a single authorised UID:

EEPROM.writeString(0,uidString);
EEPROM.commit();

And later compares it:

if (uidString == EEPROM.readString(0)){
  digitalWrite(relais, HIGH);
}

Mark summarises the behaviour clearly:

“If there is a match, then it will open the door or activate the relay.”

Design observations, Limitations and Future Improvements

Single UID storage keeps the logic simple but limits scalability
EEPROM use is appropriate for persistence across resets
The 3-second relay activation (delay(3000)) is fixed, this could be parameterised

The final application is a practical one: securing a 3D printer enclosure.

“I do have a curious kid… this way I can prevent her from opening it.”

Mark hints at broader applications but doesn’t extend the design further. There are several obvious next steps:

1. Multiple user support

Currently only one UID is stored. Expanding to a list would make this viable for shared access.

2. Security considerations

UID-based authentication can be cloned on some tags
No encryption or challenge-response mechanism

3. Feedback and UX

Add buzzer or LED patterns for success/failure
Serial output is useful but not user-facing

4. Power and enclosure

No dedicated enclosure or power regulation shown
Long-term installs would need proper housing

In Closing

This project does exactly what it sets out to do: deliver a working RFID-controlled lock with minimal overhead. It’s approachable, adaptable, and grounded in real use rather than theory.

The combination of ESP32, MFRC522, and a simple transistor driver is well understood—but Mark’s implementation shows how quickly that can become something practical.

“Present my ring… and it will open.”

That direct cause-and-effect is what makes the project useful, and easy to build upon.

Supporting Files and Links

Bill of Materials

Product Name	Manufacturer	Quantity	Buy Kit
WURTH ELEKTRONIK Tactile Switch, WS-TATV Series, Top Actuated, Through Hole, Round Button	WURTH ELEKTRONIK	1	Buy Now
Transistor BC517-D74Z	Onsemi	1	Buy Now
Resistor 1K	Multicomp pro	1	Buy Now
Diode 1n4001	Onsemi	1	Buy Now
RFID Tag KW9Z-T1X5B	IDEC	1	Buy Now
Product Name	Manufacturer	Quantity
ESP32 Doit Devkit V1
RFID reader PCB develp. Kit RC522
USB cable and USB power supply
Lock mechanism 5V	BADODO Security	1

Tags: friday_release

ESP32 + RFID = Smart Access Control in a Simple DIY Build -- Episode 706

cstanton — Wed, 18 Mar 2026 17:58:26 GMT

Revision 1 posted to Documents by cstanton on 3/18/2026 5:58:26 PM