![]() Resistors created in a batch will match well, so their ratios can be precisely defined. Absolute accuracy is not critical since the resistors are used in a voltage divider. In production, keys could be created by vapor deposition of resistive material directly onto a circuit board. Hence, the theoretical maximum number of key combinations is 7.2 × 10 16! The number of different keys is limited to 4.4 × 10 12 by practical concerns, the given standard 1% resistor values, and the allowance of a 16-LSB measurement span for each key combination. However, only eight bits of data are available on the serial bus. ![]() The seven voltage-input channels are each capable of measuring a voltage with 10-bit resolution. For simplicity, only details relating to the ADM1024 and the key are given in this diagram. The voltage dividers are embedded in a key that can be inserted into the lock, as shown in the figure. The basic principle of this lock decoder is the division of a voltage into seven specific levels that can be measured by the ADM1024. In this application, the ADM1024 is used to monitor seven voltages provided by a digital key as well as to open a lock if the correct key is inserted. It also includes a 10-bit digital-to-analog converter (DAC). This device monitors up to seven supply voltages and a 5-bit VID code. ![]() The ADM1024 was designed to monitor the local temperature, the die temperature of up to two Pentium processors, and the speed of up to two fans. The following is a simple yet powerful security system employing an ADM-1024 PC-hardware monitor as the key's decoder. Simplicity is the key to a good security system design.
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