Step 1: The Basic Idea.
-The soldering iron can be turned on with the push of a very obvious button.
-It can be turned off manually as well, with another switch.
-If I forget to use this second switch, the iron turns off automatically after X period of time.
-A light tells you that the iron is running.
-The iron and timer can be separated again with ease.
Step 2: What You Need.
A normally open push button
A normally closed push button (I didn't have one, so I used a momentary toggle switch instead)
A light for indicative purposes (choose one to suit its location in the circuit, more on this later)
Any enclosures that you want to put your device in
A power supply to suit your timer and relay
Enclosure hardware (if required) I used:
IEC socket for power in
GPO socket for power out
5 pin microphone plug and socket for cable to switch box
Step 3: The Timer
Step 4: The Relay.
To do this, take your normally open switch and your normally closed switch and solder them together in series. Also solder the normally closed contacts of the timer's relay in series, after the normally closed switch. Connect the other side of the timer relay to the coil of your 'latching' relay.
Now, connect the normally open contacts of your 'latching' relay in parallel to the normally open switch.
Step 5: Schematic
I have included two possible locations for the lamp, you could use one or both of these. Note however, that if you use lamp A, you will need to make sure it is rated to mains voltage. Lamp B must be suited to your power supply.
The lamp should be placed in one of these two positions for the following reason: The light's purpose is to tell you that the iron is hot and the mains connected to the output. If the light is too far (electrically) from the mains circuit, all it will tell you is that the timer is connected, or the wires connected to the lamp are not broken. If it close to the mains, you can tell that the mains is on, failing that, the relay is a good second option, as it will tell you that the relay is stuck on, or has failed, allowing you to turn the whole thing off before your workshop burns down.
Step 6: Put It in a Box.
Step 7: A Note on Timer Choice
If your timer does what I wanted it to do initially, you may be able to come up with a better system. Play around with it.