Bicycle alarm electronic project

This is a project that I undertook during June 1996 as my final year electronics project. The entire circuit was built using individual components including logic gate ICs and and keyboard decoder IC. Since them electronics has moved on and if this was created today most of the functionality would instead be implemented using a microprocessor / mi
Bicycle alarm electronic project - schematic

crcontroller such as the Arduino prototyping board. This is however an example of how circuits can be designed using logic components. To set the alarm the supply must be disconnected. To achieve this a transistor switch is used to disconnect the supply when the full or part set switch is pressed. This is achieved using a NOR gate (IC2D). This is a 18 pin IC which uses a matrix output type keypad. The PIN number can be separately programmed directly from the keypad. This makes programming much easier. The pin layout is shown below. The IC is CMOS compatible and has a key-in echo, which bleeps every time a key is pressed. The following circuit would have to be fairly complex to use this IC. Below is the circuit diagram if the IC was for use as a door opener. The choice of the decoder was based on two main factors. The first was the required complexity of the following circuit. As the RS7225 gave fixed output levels the IC could drive combination logic directly whereas the UA3730 would require special sequential logic to decode the outputs. The second factor was cost. The cost of the two ICs is very much the same but the cost of the required keypad was much cheaper for the telephone type keypad. Also a membrane keypad was available for the telephone type which gave a level of waterproofing. As the RS7225 required the disconnection of the supply to reset the outputs a transistor switch has been used to disconnect the supply...

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