Want to see just how profoundly the smartphone can change a trip to the bank ATM?

Head to Madison Street in downtown Chicago.

Responding to the growing use of smartphones, Wintrust Financial is rolling out 190 "cardless cash" ATMs that will give consumers the option of withdrawing cash using only their smartphones.

Wintrust, based in the Chicago suburb of Rosemont, is riding a banking technology trend for 2015, according to Mercator Advisory Group. "We anticipate the increasing convergence of ATMs and mobile banking" in what's commonly called cardless- cash access or mobile-cash access, the Maynard, Mass.-based consulting firm said in its newly released report "2015 Outlook: Banking Channels."

To make the cardless-cash transactions possible on existing ATMs, the Wintrust machines are being outfitted with software from FIS, a technology provider to banks, retailers and payment processors. FIS said Wintrust is the first of its 1,600 mobile-banking clients to roll out cardless cash on a widespread basis.

Canadian-owned BMO Harris Bank has been testing mobile cash technology with its employees and expects a "broader" rollout to ­customers in the first quarter of 2015, a BMO spokesperson said.

Wintrust, a $19 billion-asset institution with an older customer base, sees the technology as an avenue to develop relationships with its depositors' children, said Thomas Ormseth, senior vice president for noncredit services for Wintrust.

"Going forward, given the proliferation of smartphones and the user acceptance of the younger crowd, we need to be in that space," Ormseth said.

Here's how cardless-cash machines work at Wintrust:

Consumers can use their Wintrust mobile app to preset how much money they want to withdraw from the ATM on future visits. Once they arrive at the ATM, they sign into the mobile banking app on their phone with their four-digit password. On the phone, they select the cardless cash option, which then opens the smartphone's camera. Then, on the ATM screen, the customer touches the "cardless cash" button, which creates a QR code, a square matrix-style bar code. Customers hold their smartphones over the QR code on the ATM screen, tap submit, and the ATM dispenses their cash. The receipt heads straight to the phone.

The withdrawal takes about 10 seconds, compared with about 40 seconds for a traditional ATM withdrawal, Wintrust said.