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.

Money expert Martin Lewis says mobile phone customers can save money by sending a text to a 5-digit number.

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.