How to make a redstone clock that I can turn on/off with a lever?

I want to create a Redstone clock that can be enabled and disabled with a lever permanently placed down.

Here's a selection of toggleable clocks of various periods and duty cycles - make your pick.

1. tuneable period of 5+ redstone ticks, about 50% duty cycle, just change the number of repeaters.

2. 2rt period, 50% duty cycle, signal toggles between 15 and 2, so you need 2 extra redstone to make it actually switch on/off.

3. trivial observer clock, 2rt period.

4. 4rt classic repeater clock, with observer on slime block to start it up instead of your torch.

5. trivial hopper clock, 15gt (7.5rt) period.

6. Fader, a slow clock with tuneable, long period; tuneable duty cycle (power level drops gradually on output; reduce it to cut-off threshold to tune the on:off ratio)

7. Etho clock. Period of up to 255 seconds depending on amount of items in the hoppers; 2rt off, remainder on duty cycle.

Here are some of the most common designs:

You can use a sticky piston with an observer facing outwards into an empty block, and then another observer. the output of that observer is your clock. When the piston is powered (using a lever) the clock will start.