FundMe Smart Contract

A Solidity smart contract that allows users to fund an organization while ensuring that only the contract creator (manager) can withdraw the accumulated funds.

The contract enforces a minimum funding value in USD using Chainlink Price Feeds, allowing contributors to send ETH while maintaining a USD-denominated minimum requirement.

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Overview

The FundMe contract enables decentralized funding by allowing users to contribute ETH to a smart contract. Each contribution must meet a minimum USD value threshold to ensure meaningful participation.

To achieve this, the contract uses Chainlink's decentralized oracle network to retrieve the latest ETH/USD price and convert incoming ETH into its USD equivalent.

Only the contract owner (deployer) has permission to withdraw the collected funds.

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Key Features

• Accept ETH contributions from any user
• Enforce a minimum funding requirement of 5 USD
• Convert ETH to USD using Chainlink Price Feeds
• Track contributions made by each address
• Restrict withdrawals to the contract owner
• Automatically handle direct ETH transfers using receive() and fallback()
• Gas-efficient withdrawal implementation

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Smart Contracts

FundMe.sol

The primary contract responsible for:

• Accepting ETH contributions
• Enforcing the minimum USD funding requirement
• Tracking contributors and their funded amounts
• Allowing the contract owner to withdraw funds

Main Functionalities

Funding

function fund() public payable

Users can send ETH to the contract through this function. The contract checks whether the ETH value sent meets the minimum USD requirement using a price conversion library.

require(msg.value.getConversionRate() >= MINIMUM_USD, "Didn't send enough ETH");

If the requirement is met:

• The sender is recorded as a funder
• Their contribution is stored in a mapping

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Withdrawal

function withdraw() public onlyOwner

Only the contract owner can withdraw funds. The withdrawal process:

1. Resets all recorded contributions
2. Clears the funders list
3. Transfers the entire contract balance to the owner

The transfer is performed using the recommended call method.

(bool callSuccess,) = payable(msg.sender).call{value: address(this).balance}("");
require(callSuccess, "Call failed");

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Access Control

The onlyOwner modifier restricts withdrawal functionality to the contract deployer.

modifier onlyOwner()

A custom error is used for gas efficiency.

error NotOwner();

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Receive and Fallback

The contract supports direct ETH transfers.

receive() external payable
fallback() external payable

Both functions automatically redirect the transaction to the fund() function.

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PriceConverter.sol

A Solidity library that handles ETH price retrieval and conversion.

The library integrates with Chainlink's AggregatorV3Interface to obtain the latest ETH/USD price feed.

Main Functions

Get ETH Price

function getPrice() internal view returns(uint256)

Fetches the latest ETH price from Chainlink and converts it into an 18-decimal format for consistency with Solidity's wei units.

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Convert ETH to USD

function getConversionRate(uint256 ethAmount) internal view returns(uint256)

Converts an ETH amount into its USD equivalent using the latest price feed.

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Get Feed Version

function getVersion() internal view returns(uint256)

Returns the version of the Chainlink price feed being used.

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Chainlink Integration

The contract uses the ETH/USD Chainlink Price Feed to obtain reliable off-chain price data.

Price Feed Address:

0x694AA1769357215DE4FAC081bf1f309aDC325306

This ensures that the minimum funding requirement is based on real market price data rather than hardcoded values.

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Minimum Funding Requirement

The contract requires each contribution to be worth at least 5 USD.

uint256 public constant MINIMUM_USD = 5e18;

This value represents $5 with 18 decimal precision, matching Ethereum's wei denomination.

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Security Considerations

• Only the contract owner can withdraw funds
• Funding must meet a minimum USD value
• State changes occur before transferring funds during withdrawal
• Uses Chainlink's decentralized oracle network for accurate price data
• Custom errors reduce gas costs compared to revert strings

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Deployment

1. Compile the contracts using Solidity ^0.8.18
2. Deploy the FundMe contract
3. Send ETH using the fund() function or direct transfers
4. Withdraw funds using the withdraw() function (owner only)

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Requirements

• Solidity ^0.8.18
• Chainlink Contracts

Recommended development environments:

• Remix
• Hardhat
• Foundry