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This 1.5 volt led fasher runs more than a year on a single d" cell and alternately flashes 2 LEDs at about a 1 second rate. The circuit employs a 74HC14 CMOS hex inverter that will operate at very low voltages (less than 1 volt). One section is used as a squarewave oscillator (pins 1 and 2), while the others are wired to produce a short 10mS pulse on alternate edges of the square wave so the LEDs will alternate back and forth. The output sections each use a capacitor charge pump to increase the voltage for the LEDs. The circuit draws an average current of 800uA from the D battery and the LED peak current is about 40mA with a fresh battery and drops to about 10mA as the battery voltage falls to 1.1 volts. The capacity of a alkaline D cell is about 12 amp hours with a cutoff voltage of 1.1 so the circuit should run about 12/.0008 = 15000 hours or maybe 625 days, but I havent verified that yet. The idea for this circuit came from a single 1.5 volt LED flasher by Dave Johnson that can viewed at

This Simple 5 Digit Alarm Control keypad Circuit Diagram switch will suit the Modular Burglar Alarm schema.However, it also has other applications. The Keypad must be the kind with a common terminal and a separate connection for each key. On a 12-key pad, look for 13 terminals. The matrix type with7 terminals will NOT do. Choose the five keys you want as your code, and connect them to `A, B, C, D & E`.

5 Digit Alarm Control keypad Circuit Diagram



Wire the common to R1 and all the remaining keys to `F`. Because your choice can include the non-numeric symbols, almost 100 000different codes are available. The Alarm is set using the first four of your five chosen keys. When `A, B, C & D` are press edin the right order and within the time set by C1 and R2 (about10 seconds), current through R11 switches Q6 on. The relay energizes, and then holds itself on by providing base current forQ6 through R12.

The 12-volt output switches from the “off” to the “set ” terminal, and the LED lights. To switch the Alarm off again it is necessary to press A, B, C, D & E in the right order. The IC is a quad 2-input AND gate, a Cmos 4081.These gates only produce a high output when both inputs are high.Pressing `A` takes pin 1 high for a period of time set by C1 andR2. This `enables` gate 1, so that when `B` is pressed, the output at pin 3 will go high. This output does tw1o jobs. It locks itself high using R3 and it enables gate 2 by taking pin 5high.

The remaining gates operate in the same way, each locking itself on through a resistor and enabling its successor. If the correct code is entered within the time allowed, pin 10 will switch Q5 on and so connect the base of Q6 to ground. This causesQ6 to switch off and the relay to drop out. Any keys not wired to `A, B, C, D or E ` are connected to the base of Q4 byR9. Whenever one of these `wrong` keys is pressed, Q4 takes pin 1low. This removes the `enable` from gate 1, and the code entry process fails. If C, D or E is pressed out of sequence, Q1, Q2 orQ3 will also take pin 1 low, with the same result.

You can change the code by altering the keypad connections. If you make a mistake entering the code, just start again. If you need a more secure code you can use a bigger keypad with more `wrong`keys wired to `F`. A 16-key pad gives over half a million different codes. All components are shown lying flat on the board; but some are actually mounted upright. The links are bare copper wires on the component side. tw1o of the links must befitted before the IC.