Chainlink Aggregator

Aggregator.sol

pragma solidity ^0.6.0;

import "@chainlink/contracts/src/v0.6/dev/AggregatorInterface.sol";

contract MyContract {
  AggregatorInterface internal feed;

  constructor(address _aggregator) public {
    feed = AggregatorInterface(_aggregator);
  }

  function getLatestAnswer() public view returns (int256) {
    return feed.latestAnswer();
  }

  function getLatestTimestamp() public view returns (uint256) {
    return feed.latestTimestamp();
  }

  function getPreviousAnswer(uint256 _back) public view returns (int256) {
    uint256 latest = ref.latestRound();
    require(_back <= latest, "Not enough history");
    return feed.getAnswer(latest - _back);
  }

  function getPreviousTimestamp(uint256 _back) public view returns (uint256) {
    uint256 latest = ref.latestRound();
    require(_back <= latest, "Not enough history");
    return feed.getTimestamp(latest - _back);
  }
}

Working ETH/USD price feed contract on Rinkeby 0x0bF4e7bf3e1f6D6Dc29AA516A33134985cC3A5aA