OR with diodes

Its also easy to implement an OR circuit. This is even easier to understand, than the previous AND circuit. We just need to move a few bricks. These circuits can be problematic, because the output voltage (level) are no longer compatible, when combined with additional follow up logic functions. Additional transistors can solve the problem. They amplify the output signal again and a DTL (Diode-Transistor-Logic) will result. In the following circuit it does not matter which push button is pressed. The red LED lights up always when one or the other or both buttons are pressed. If no button is pressed, the LED is off. This is a simple OR function.