tri-state voltage comparator

It is often necessary, particularly when experimenting with circuits, to make connection between the output of one circuit and the input of another which is at a different DC level. If the signals involved in the circuit are AC signals this is no problem, a capacitor can be used to isolate the DC levels while allowing AC signals to pass. However, when dealing with DC or very low frequency AC signals the solution is not so easy, and it is in these cases that this little gimmick will prove useful.