Voltage drop when using relay - Motors, Mechanics, Power and CNC

Hi! I'm having a issue using arduino, relay and sensors. Everything works as expected from the logic point of view: sensor reads, relays close/opens, etc. The problem is the current draw of the relay and the voltage drop in the microcontroller, which impacts on the sensor readings drastically. When the relays are closed i see almost 5.1V on arduino vcc pin. If I turn on the relay, the VCC voltage drops to 4.3 v I'm learning about electronics so the questions are: what is the best elect

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