Some toasters have a simple timer circuit that releases an electromagnet to trigger the toast to pop up. There is usually a resister to adjust darkness that con

Some toasters have a simple timer circuit that releases an electromagnet to trigger the toast to pop up. There is usually a resister to adjust darkness that controls how long the timer runs. The cheapest toasters apply current to a bimetallic strip that heats up and bends away from the contact causing the heating to stop and the toast to pop up. These are variable due to ambient temperature and because the bimetallic strip is still warm if you do a second batch of toast and will trigger too soon. These are both indirect proxies for doneness of the toast, not a direct measure like the toaster featured in the article.