Learning how to use mostly discrete components instead of a microcontroller would be the core objective to build this circuit outside of needing a key-code access point or other secure 12 V relay ...

Financial guru Martin Lewis is encouraging individuals to send a text message containing a five-digit code in order to reduce their mobile phone bills.

Speaking on his ITV programme, The Martin Lewis Money Show, he said people could save hundreds each year by simply texting a 5-digit code.