ATLANTA —  From a bloody attack on an Alabama bridge to a bill-signing ceremony in the White House, a new exhibit traces the history of the federal Voting Rights Act (search) on the eve of its 40th anniversary.

Organizers of the free exhibit, which opens Thursday at the Martin Luther King Jr. (search) historic site, say they hope to show both the difficult struggle to pass the law and the lasting effects it has had.

"What we're really hoping people come out with is not just that it was a struggle, but that overall, it was a successful struggle," said Dean Rowley, co-curator of the exhibit, "Of Ballots Uncast: The African American Struggle for the Right to Vote".

The act, signed by President Lyndon Johnson (search) on Aug. 6, 1965, officially guaranteed the right to vote to every American, regardless of race. Its basic tenets are permanent, but certain provisions must be renewed by Congress by 2007.

At the exhibit, visitors will enter via a replica of Alabama's Edmund Pettus Bridge (search) in Selma, site of the "Bloody Sunday" attack in March 1965. Alabama state troopers stopped civil rights marchers on the bridge, turning them back using nightsticks and tear gas.

"It was really the Bloody Sunday march that got the nation's attention and raised interest in getting the Voting Rights Act passed," Rowley said. "People didn't want to be associated with something so oppressive."

The exhibit's displays include Johnson's copy of his speech to Congress pushing the act, complete with his handwritten changes, and an ink pen Johnson used to sign the bill into law.

It also chronicles both legal and illegal means used to keep blacks away from the polls before the act passed.

There's an authentic Ku Klux Klan uniform and an interactive recreation of the "jelly bean test," a technique used by some Jim Crow-era registrars to prevent blacks from voting. The registrar would ask voters to guess the number of jelly beans in a jar.

"The tendency was for white voters to somehow get it right and for black voters to get it wrong," Rowley said.

A reception for the exhibit on Thursday will feature an address by U.S. Rep. John Lewis (search), a Georgia Democrat who was injured during the "Bloody Sunday" attack and is leading the effort in Congress to reauthorize the act.

One part set to expire requires governments with a history of racial discrimination to get approval from the federal government before changing their voting laws or district lines. The provision affects most states in the South, and parts of other states including New York and California.