CMOS inputs on virtually all CMOS devices, from the humble 74HC00 to super complex microcontrollers, incorporate protection diodes internally to GND and to VCC.  Not all data sheets show them, but they are there to protect the device from being damaged by any over voltage on the input however brief.  Is it OK to actually use these diodes – yep.  […]

Higher Voltage Inputs A 74HC4049 or 74HC4050 can be powered at 2V to 6V and will accept input voltages up to +16V  (pin out is same, 74HC4049 just inverts the logic state). 4049 is basically the same but consumes a bit more current and has a min supply voltage of 3.5V. Higher Voltage Outputs Low […]

Project HiJack – A Great Power And Data Transfer Project http://www.eecs.umich.edu/~prabal/projects/hijack/

3V Devices to 5V CMOS 4 connections: 74HCT125 is a good cheap choice (14 pin package, quad 3-state buffer).Power at 5V. Connect each of the 4 output enable pins to 0V. The min high input voltage is 2V so 3V3 compatible and the output state matches input state (it’s a straight buffer). 74HCT08 (quad AND […]