Joel Reed used a crowbar and screwdriver to smash his way into a rear office within Monarch Coin Laundry on Mill Road on 24 March.
He ransacked the room looking for cash and made off with just £15 but as he was leaving the shop, two members of the public entered, and he pointed a knife at them.
The pair ran out of the store, as another member of the public arrived, and hid around the corner to call the police. They then watched Reed make off on a bike.
Reed was arrested at his home in Cromwell Road, Cambridge after being identified on CCTV. The shoes that he was wearing upon his arrest also matched footprints at the scene.
At Peterborough Crown Court on Thursday, Reed, 30, was sentenced to three years in prison after previously pleading guilty to aggravated burglary and possession of a blade in a public place.
