A disposable cassette for mixing a drug in a vial includes a liquid inlet for connection to a liquid supply, a first vial spike, a second vial spike, a chamber and a valve mechanism. The brake pedal assembly is further provided with a preload spring configured to provide a preload force to the brake pedal arm and a preload adjustment cam in cooperation with the brake pedal arm. The circuit layer may employ a link layer to send data packets over links to other network nodes.