Two button control systems are often used on industrial presses to keep the operator’s hands away from the dangerous parts of these machines. Just for hobby purpose I designed a logic gates circuit that activates an output if two buttons are pressed simultaneously (with a small tolerance).
Transistors and capacitors are used for delay function. The input pin of the gate number 7 takes the high level one seconds after the output number 5 is activated; the input pin of the gate number 8 gets high five seconds after the activation of the output number 4.
If a button is pressed and the other one is not pressed within a short time, the gate number 7 disables the output signal through the gate number 2. If the buttons are pressed almost simultaneously the gate number 7 is disabled by the gate number 6. After five seconds the gate number 8 disables the output through the gate number 3. So the operator has to release the buttons and press them again.
For safety reason each button features a second contact, which works directly on the relay coil. As I said, this is just an hobby project and should not be used on real equipments. To be in compliance with the law use certified devices only.