Here’s an easy-to-build circuit to drive a solid-state relay for a period that can be selected as two, four, or six hours. This device forms part of a project by the author to control a heating system remotely by telephone (for a holiday home). The aim of the circuit is to avoid the risk of the heating’s running for more than a certain time if, in the event of a problem, there is no-one to stop it or put it into frost protection position.
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