Sajee tronics

Check the Phone Line with a Multimeter      Before you try to tap into the electricity in the phone line, you should check it with a multimeter to see what you are working with. Start by cutting open a phone cord and separating the internal wires. In most cases you will have one red wire and one green wire. Strip the insulation off the ends. Then plug the cord into a phone jack and use a multimeter to measure the output voltage. Then I hooked up various resistors to see what the output would be with different loads. I determined that the supply voltage isn't regulated. This means that the voltage changes depending on the resistance of the circuit that it is powering. After some calculating, I worked out that the base signal coming out of my phone jack pretty closely resembles a 52 Volt DC source with a 628 ohm internal resistance. Basically this means that I can run a 12V circuit at 64mA, a 9V circuit at 68mA, or a 5V circuit at 75mA. This isn’t a lot. 

Next, upload the following sketch to your Arduino and open the serial monitor window in the IDE: // -------------------------------------------------------- #include <SoftwareSerial.h> SoftwareSerial RFID(2, 3); // RX and TX int i; void setup() { RFID.begin(9600); // start serial to RFID reader Serial.begin(9600); // start serial to PC  } void loop() { if (RFID.available() > 0)  { i = RFID.read(); Serial.print(i, DEC); Serial.print(" "); } } // -------------------------------------------------------- Reading and recognising RFID cards To do anything with the card data, we need to create some functions to retrieve the card number when it is read and place in an array for comparison against existing card data (e.g. a list of accepted cards) so your systems will know who to accept and who to deny. Using those functions, you can then make your own access system, time-logging device and so on. Let’s demonstrate an example of this. It will check

The listings at Amazon and other online vendors show this inexpensive membrane keypad as  "4x4 Universial 16 Key Switch Keypad Keyboard For Arduino." There was no documentation  for the product, nor were there any links from Amazon. Here are my notes on how to connect  and test this keypad. The arrangement of the keys is 1 2 3 A  4 5 6 B  7 8 9 C  * 0 # D There is a ribbon with 8 wires running from the bottom of the keypad. With the keypad face up,  the wires connect in sequence from left to right to Arduino digital pins 2 - 9. Don't use digital  pins 0 and 1 on the Arduino Uno, since they are used for serial communication. The Arduino Keypad library is available from the  Arduino Playground .  The following code will allow you to test the keypad. As each key is pressed, the corresponding  character should appear on a separate line in the Arduino IDE's serial console. #include <Keypad.h> const byte ROWS = 4;  const byte COLS = 4;  char keys[ROWS][CO