"I hit upon the idea of a chocolate bar dispenser, but replacing chocolate with cash."
He later sold his concept for an automatic teller machine, now known as an ATM, to Barclay’s Bank more than 40 years ago.
The first ATM was installed at a branch of Barclays in a north London suburb on June 27, 1967.
Plastic bank cards had not been invented yet, so the machine used special cheques chemically coded with a mildly radioactive material.
The machines were designed to recognise the cheques once customers entered a personal identification number (PIN).
Shepherd-Barron originally planned to make the PIN numbers six digits long, but he cut the number to four after his wife suggested that six was too many.
"Over the kitchen table, she said she could only remember four figures, so because of her, four figures became the world standard," he once told the BBC.
Shepherd-Barron was born in India in 1925 to Scottish parents. He worked for the banknote printer De La Rue and was acknowledged by Queen Elizabeth in 2005 for his contributions to banking.
When Shepherd-Barron first started producing his cash machine, it was not long after that companies all over the world began to pick up on his idea.
"His invention has transformed the way that we get hold of our cash," a spokesman for Link, Britain's cash machine network, said.
"While cash machines were once a novelty, they have become part of daily life."
Today, there are at least 1.7 million ATM machines around the world.