vending machine: mapping and affordances

This is a vending machine on the first floor of McAfee Hall. Users can see, through the clear glass front, that it dispenses snacks (an affordance). The snacks are displayed in a grid format, with labels underneath each one with a letter and a number (for example, A5). It has a panel on the side for users to interact with, consisting of a keypad with keys for all letters and numbers represented on the grid, a small screen displaying one line of text, and slots to receive bills and coins as well as a button. On the glass there is a sticker point at the keypad with arrows saying “Press selection # for price”. At the bottom, there is a hinged panel with “PUSH” engraved on it, and in the bottom right hand corner a smaller hinged panel.

Although there is not a lot of hinting to the inner workings of the machine, through the printed instructions and relative minimal design the user can fairly simply create a mental mapping of how it works. You feed it money, and the product drops down to the space behind the PUSH slot, where the user can access it. Another possible function is to press the button to retrieve change in the smaller slot, although this isn’t immediately clear and would probably take experience to know. The sticker with instructions, as well as the keypad corresponding to the labels, explained the function of the machine, but it could have been more difficult if the user did not speak English or had not used a machine before. As for what to do first, I think it might not matter whether you put in money or type in a code first (typing in the code at first gives the price of the product, ranging from $0.85 to $2.50), but the machine doesn’t make clear either way. The only way for the user to discern feedback is through the small one-line screen, which reads “Ready” or “Coins only” (alternating very slowly, so the user might not see the instructions on the latter). As for feeding the money, there are also instructions (English) printed on the bill slot, and the coin slot is designed as such that it should be clear only coins can fit through the slot.

The power draw of the machine is around 106 kilowatts, according to a Texas A&M evaluation here. Compared to a laptop, which is around 50, 106 thousand for a vending machine seems like a lot, although I suspect the inner workings may be a lot more complex than my simple mental mapping needs to know.

Overall I would find the product simple to use because of experience, although the “Coins only” may have thrown me off if I had not seen it. Considering the machine is essentially a large box with buttons, the implicit design of its functions requires either instructions or experience to understand, which is a bit problematic for a user interface. Perhaps some mechanism that implied the money going into the snack, or somehow more clearly connecting it, would help, or an interface where the purpose of  the buttons (i.e. the change button).