Author Archives: Richard Teel

Magnetic Card Reader (TTL) with Arduino


I was cleaning up and found a project I abandoned about 20 years ago. I was attempting to read magnetic strip cards using the PC Parallel Port. I had done it previously with a different card reader but I had some trouble with these two particular units. I wanted to test them before I decided to get rid of them so I broke out an Arduino Nano and found the magstripelib library written by Carlos Rodrigues on GitHub. I could not get the readers to work with the code so I looked at the libraries but found no issue with them. I then found an issue with the hardware that was rather easy to solve.

The Magnetic Card Readers

I purchased the card readers from either All Electronics or Electronic Goldmine. (Both places are great for obtaining low cost surplus electronics.) The readers are made by Tokin and have a part number of MCS-131P-3. The PCB contains 1550-B014-00-1 and YEC YE-34V N markings.

Card Reader Left Side View   Card Reader Top View   Card Reader Right Side View

I had recalled that there was an issue with the connector cable on the readers that I wanted to resolve. The red wire is connected to ground and the brown wire is connected to Vcc (+5V). This was verified by checking with an ohm meter. Additionally, there is a card sense connection but there is no wire. With a simple modification, we can switch the wires and add a new wire for the card sense connection. While we are at it, We will make the readers breadboard friendly by changing the connector to a 5 pin male header.

Modifying the Magnetic Card Reader

Step 1 – remove the PCB

Use a plastic tool or very carefully use a screwdriver to remove the hot glue holding the PCB in place and carefully slide the card out of the reader.

Card Reader Right Side View   Plastic Tool   Separating PC Board

Once the card is free, you can see that the board layout is made to accommodate the correct connections but there was an effort made to switch the ground and Vcc wires.

Separated PC Board   Close-up of the wires connecting to the PCB

Step 2 – Remove the strain relief zip-tie

Cut the zip-tie and remove.


Step 3 – Switch the red and brown wires

Unsolder the red and brown wires, switch them, and solder in place.


Step 4 – Add the card sense wire

Cut a length of stranded 26 AWG wire, strip the ends and solder to the card-sense connection.

Step 5 – Add the strain relief

Use a zip-tie to reapply the strain relief to the wire connector using the two holes in the PCB.


Step 6 – Reinstall the PCB

Carefully return the PCB to the plastic assembly by reinserting into the slot.

Step 7 – Remove the old connector

Cut off the old connector.

Step 8 – Prep the wires

Strip the ends of the wire and tin with solder.

Step 9 – Cut Heat-Shrink Tubing

Cut 5 pieces of 1/16″ heat-shrink to about 1/4″ in length and one or two pieces of 3/16″ heat-shrink tubing about 3/4″ in length.

Step 10 – Prepare male header pins

Cut a single-row male header to 5 positions.

Step 11 – Solder wires to header

Tin the short pins with solder. Slide the 3/16″ heat-shrink piece(s) over all of the wires together. Solder each wire to the tinned header pins by first sliding a 1/16″ heat-shrink tubing over each wire.

Step 12 – Shrink the heat-shrink tubing

You may want to use a breadboard to keep the pins aligned while heating the tubing as the plastic may become pliable and allow the pins to move. Heat the tubing to fix them in place.

Testing with the Arduino

Wire up the Arduino

The wiring will depend on the processor on the Arduino. If you are uncertain as to which processor your Arduino has, check out the Wikipedia article at

The Arduino Nano uses the following wiring.

Wire Color Function Arduino Pin
Brown Ground GND
Red Vcc 5V
Green Card Detect 4
Orange Strobe 3
Yellow Data 2

Load the example sketch

Connect the Arduino to the PC and start the Arduino IDE and add the magstripelib library by going to the menu Tools > Manage Libraries… Search for MagStrip and install the library by Carlos Rodrigues.

Find and Install MagStripe Library

Load the MagStripe example by going to the menu File > Examples > MagStripe > MagStripeReader.

Make certain the correct board and port are selected then upload the code to the Arduino. Once the code is loaded, open the serial monitor and run a card through the reader to see if there is any data read. I did not receive any data so I added some lines of code to let me know that there was an issue. Below is the modified code. The modified code let me know that the card was detected and it attempted to read it but ran into an issue decoding the data.

 * MagStripeReader - Read data from a magnetic stripe card (track 1, 2 or 3).
 * Copyright (c) 2010 Carlos Rodrigues <>
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.


// Visual feedback when the card is being read...
static const byte READ_LED = 13;
static const byte ERROR_LED = 12;

MagStripe card;

 * Track 3 is the one that can contain the most characters (107).
 * We add one more to accomodate the final '\0', as the data is a C string...
static const byte DATA_BUFFER_LEN = 108;
static char data[DATA_BUFFER_LEN];

void setup()
  pinMode(READ_LED, OUTPUT);
  // The card data will be sent over serial...
  // Initialize the library for reading track 2...

  // Start with the feedback LEDs off...
  digitalWrite(READ_LED, LOW);
  digitalWrite(ERROR_LED, LOW);

void loop()
  // Don't do anything if there isn't a card present...
  if (!card.available()) {
  // Show that a card is being read...
  digitalWrite(READ_LED, HIGH);
  // Read the card into the buffer "data" (as a null-terminated string)...
  short chars =, DATA_BUFFER_LEN);
  // Show that the card has finished reading...
  digitalWrite(READ_LED, LOW);
  Serial.println("-- Read Completed --");
  // If there was an error reading the card, blink the error LED...
  if (chars < 0) {
    digitalWrite(ERROR_LED, HIGH);
    digitalWrite(ERROR_LED, LOW);
    Serial.println("Read Error...");

  Serial.println("Good Read...");
  Serial.print("Read Direction: ");
  Serial.println(card.read_direction()==1 ? "Forward" : card.read_direction()==2 ? "Backward" : "Unknown");

  // Send the data to the computer...

/* EOF - MagStripeReader.ino */

The result was always a failed read no mater which card was read.

-- Read Completed --
Read Error...


As mentioned in the introduction, I first focused on the code to see if I could find something that was amiss. I also attempted to switch the strobe and clock wires to see if I had identified them incorrectly. I then tried using an Arduino Uno to see if the Nano was a problem but I still could not successfully read a card. I then turned my attention to the hardware. The first thing that I did was to use my Tenma 72-8705 oscilloscope to look at the strobe and data lines. I noted that it looked like the data line had narrow spikes on some clock edges. I did not think much of it at the time.

Channel 1 is Strobe and Channel 2 is Data

I decided to break out the Saleae Logic Analyzer to capture the strobe and data lines and manually decode the data to see if the readers are working properly. I saw the same spikes on the data line which occurs with the rising clock edge.

Channel 0 is Strobe, Channel 1 is Data, and Channel 2 is Card Sense

Since the spikes occur on a rising clock edge, it really should not be an issue as the data is only valid on a falling clock edge. I exported the captured data into a CSV file and looked at it in Excel. I was able to decode the data and verified that the data was reading the card properly. To know that the data was read properly, it was necessary to read some of the information from Magtek.

I took another look at the code and see that the data values are being flipped from the previous value. I was unable to determine what the width of the spikes are but I suspect that the spikes may flip the data value in the code but are not wide enough to raise the hardware interrupt on the Arduino when it returns to +5V. If this is the case then it is understandable why there are issues reading the cards. This could be fixed using hardware or software. I took the hardware approach by connecting a 0.01uF capacitor between the data line and Vcc. Once the capacitor was added to remove the spikes from the data line, the code was able to read the cards successfully.

Going Further

It may be possible to resolve the issue observed with this particular card reader by removing the interrupt from the data pin and reading the data value on the clock interrupt instead. This in turn would free up the hardware interrupt used for the data pin and allow any digital pin to be used for the data line. This may allow the reading of two track from readers which read multiple tracks or allow the use of more than one card reader.

Part II ->

eBay Review – 1602 Serial Blue Backlight LCD Display Keypad 4 Arduino Uno R3 Mega 2560 Shield

I purchased an LCD Shield for Arduino from eBay a few weeks ago. I wanted to do a review to help others to get the shield to run on their Arduino or other microprocessor.

Overall Impression

Works as stated and is a good value. I would recommend this shield if you are in the market for a low cost shield with buttons for user input. It is a great shield to get a project going.


I am not certain who designed the original shield but I assume that it is open-source as there are many similar shields on the market. It appears that most are built from the same schematic that I found on SainSmart’s website at

The shield uses one analog pin to determine which of the five switches the user has pressed. A series of resistors creates a voltage divider which in turn creates specific voltages for each switched pressed. The pins in use on the board are as follows.

Pin Function Pin Function
Reset Reset Button 10 LCD – Backlight
5V Power 9 LCD – Enable
Ground Ground 8 LCD – RS
A0 Buttons 7 LCD – D7
-LEFT 5 LCD – D5
– UP
4 LCD – D4
 WARNING: The shield works on 5VDC. Not all Arduinos are 5V tolerant so you may damage your Arduino if you use this shield on an Arduino with a microcontroller running on 3.3V such as the Due. If you do not know what voltage the microprocessor on your Arduino is running at, check the Wikipedia article at

Code for Testing

The following code was found on SainSmart’s website. It was modified slightly to monitor the value of the A0 pin over the serial connection with the PC.

  The circuit:
 * LCD RS pin to digital pin 8
 * LCD Enable pin to digital pin 9
 * LCD D4 pin to digital pin 4
 * LCD D5 pin to digital pin 5
 * LCD D6 pin to digital pin 6
 * LCD D7 pin to digital pin 7
 * LCD BL pin to digital pin 10
 * KEY pin to analogl pin 0

#include <LiquidCrystal.h>

LiquidCrystal lcd(8, 13, 9, 4, 5, 6, 7);

char msgs[5][16] = {"Right Key OK ",
                    "Up Key OK    ",               
                    "Down Key OK  ",
                    "Left Key OK  ",
                    "Select Key OK" };

int adc_key_val[5] ={50, 200, 400, 600, 800 };
int NUM_KEYS = 5;
int adc_key_in;
int key=-1;
int oldkey=-1;

void setup()
  // open the serial port at 9600 bps:
  lcd.begin(16, 2);
  lcd.print("ADC key testing"); 


void loop()
  adc_key_in = analogRead(0);    // read the value from the sensor 
  key = get_key(adc_key_in);  // convert into key press
  if (key != oldkey)   // if keypress is detected
    delay(50);  // wait for debounce time
    adc_key_in = analogRead(0);    // read the value from the sensor 
    key = get_key(adc_key_in);    // convert into key press
    if (key != oldkey)    
      lcd.setCursor(0, 1);
      oldkey = key;
      if (key >=0){

// Convert ADC value to key number
int get_key(unsigned int input)
    int k;
    for (k = 0; k < NUM_KEYS; k++)
      if (input < adc_key_val[k]) { return k; } } if (k >= NUM_KEYS)k = -1;  // No valid key pressed
    return k;

The code does not perform any debouncing of the button presses so you may need to modify the code if it becomes a problem in your project. Another limitation is the shield and/or the code will not be able to determine if more than one switch has been pressed. I have not tested this, but my hypothesis is that the switch with the lowest resistance will be detected.

Issue with 3.3V Adruino Boards

First off, read the warning above as you may damage your Arduino if the microcontroller is running at 3.3V.

After receiving the shield from the seller, frentaly , on eBay, I pulled out my Arduino Due as it happened to be the first Arduino board that I grabbed. I ran the above code and had some strange results. Pressing the “SELECT” button did nothing. Pressing the “LEFT” button registered “SELECT” was pushed. Likewise, pressing “DOWN” registered that the “LEFT” button was pressed. The “UP” and “RIGHT” buttons worked as expected. I sent a message to frentaly as I believed there was a problem with the shield. I then observed that the resistors for the voltage divider were the correct values so I pulled out a Mega board and ran the same test sketch. I found that the LCD button shield worked as expected on the Mega board. I did some investigating and found that the microprocessor on the Due board is running at 3.3V therefore the highest voltage that may be read on any analog pin is 3.3V. I went a bit further to get a bit more information.

The table below provides some information regarding the ADC values reported on A0 with 5V and 3.3V microprocessor Arduino boards. In the table below there is not difference between no button pressed and the “SELECT” button being pressed.



R (Ohms)

Total R




ADV 3.3V

NONE R2 Open Infinite  




SELECT R6 3,300 5,250





LEFT R5 1,000 1,950





DOWN R4 620 950





UP R3 330 330










Here are some slides which provide some details on how the buttons work on the shield.

  • No buttons pressed
  • RIGHT button pressed
  • UP button pressed
  • DOWN button pressed
  • LEFT button pressed
  • SELECT button pressed

The schematic is from the SainSmart web page referenced above.

Below is the data presented above shown in a different format.

Setting up ESP32 with Arduino IDE

I purchased a few things on eBay recently, including some ESP32s for $7.99 each from eBay seller, miniduino. I have not worked with the ESP32 but I know that it can work with the Arduino IDE and can run CircuitPython. I am familiar with the Arduino IDE so I wanted to get the ESP32 to work with the Arduino IDE so I can test them out and make certain that they work fine.

Doing a Google search on ESP32 and Arduino IDE returned many results which helped to get me going. The process for getting the ESP32 up and running is nearly the same as with the Teensy boards. The exception is that the Teensy boards have one nice executable to get things setup. The high-level steps to get ESP32 working with Arduino are the following.

  1. Install the latest Arduino IDE if you do not already have it installed. (
  2. Depending on your operating system, you may need to install the driver. I am running Windows 10 so I needed to install the driver for the Silicon Labs CP2102 from
    BTW: The boards that I purchased have no markings on the CP2102 chip. I fear that the chips are counterfeit or a lower grade chip. The first one I tested works so I’ll keep my fingers crossed.
  3. Once the driver was installed, I needed install the Arduino libraries for the ESP32 by cloning the GitHub repository at
    NOTE: A better way it to follow the “Installation instructions using Arduino IDE Boards Manager” instructions on the GitHub page.
  4. Program the ESP32 with the blink example.
    1. Load the blink example in the Arduino IDE and modify the example to use pin 2 for the led.
  Turns on an LED on for one second, then off for one second, repeatedly.
  This example code is in the public domain.
// Pin 13 has an LED connected on most Arduino boards.
// Pin 11 has the LED on Teensy 2.0
// Pin 6  has the LED on Teensy++ 2.0
// Pin 13 has the LED on Teensy 3.0
// give it a name:
int led = 2;

// the setup routine runs once when you press reset:
void setup() {                
  // initialize the digital pin as an output.
  pinMode(led, OUTPUT);     

// the loop routine runs over and over again forever:
void loop() {
  digitalWrite(led, HIGH);   // turn the LED on (HIGH is the voltage level)
  delay(1000);               // wait for a second
  digitalWrite(led, LOW);    // turn the LED off by making the voltage LOW
  delay(1000);               // wait for a second
  1. Pick the “ESP32 Dev Module” from the “Boards” menu option
  2. Select the COM port for your board
  3. Upload the program to the ESP32 by clicking the upload button then press and hold the boot button on the ESP32 board. You may release the button once the upload starts.