In the 1980s, before MRT was in operation and before stored-value cards were in use, the main mode of public transport was the bus, and the only mode of payment was via coins. Commuters had to ensure they had enough coins before boarding the bus, because no change would be given. I remember the fare for a feeder bus service was $0.15, so if you put in $0.20, the $0.05 became extra revenue for the bus company.
At that time coin changing machines were placed in all the bus interchanges so that commuters who needed coins could change their notes for coins. The coin changing machine was very easy to operate – no instruction manual was needed, nor was any representative from the bus company needed to stand there to guide the users. The user would insert a $1 note (back then $1 was in notes, not coins) and the machine would return the same value in coins. The hawkers or stall holders operating near the bus interchanges loved these machines too because they could change for coins for free, compared to queuing in the bank and paying a fee for the coins.
Later farecards (the card used before ezlink cards) were introduced, and people switched to using farecards, thus reducing the need to pay by coins. Eventually the coin changing machines vanished from the bus interchanges and were forgotten by many. I tried finding a picture of the machine on Google for this post but unfortunately I could not find any.