# EXPERIMENT 3

Try building this circuit and see what happens when you turn the input switches on and off. Note how the diodes allow the input signals to flow from the switches to the output but not back the other way.
This is a simple form of logical "or" gate. It has a number of drawbacks, though:
* It uses a lot of power, because current is flowing in the resistor whenever any of the inputs is high.
* It's not very fast. You may have noticed that the output takes some time to go from high to low. That's because the charge that's built up in the output connection has to leak away through the resistor. This time can be reduced by using a lower value resistor, but then the circuit uses even more power.
* All the power to drive the output comes from the inputs. In a complicated circuit with lots of gates this can be a serious problem, because often the output of one gate needs to drive the inputs of many others, and if the gates are all like this, it mightn't have enough power to do so.
In the next few lessons, we'll learn about ways to solve all of these problems.