I am trying to send data from an Arduino to a 433MHz receiver which is connected just to a battery and a LED, my goal is to send a high or low voltage through the RF units in order to make sure I can control the LED from the Arduino. My question is mainly: what do I send in order to get a low (or rather low) output? And what should I send to get a high (or rather high) output?
And would this be possible in general? Or is there something I am not seeing?
The commonly available 433 MHz receivers can't do what you want. They are very sensitive and when a strong signal is not present, simply switch on and off randomly in response to radio frequency noise.
Adafruit has some encoded TX/RX pairs that use a pushbutton keyfob transmitter (controllable with Arduino). They would probably work for you. Here are some examples:
I think you could.
A board like this
has a TTL Data output. As long as you were Continuously sending a valid data stream for it to receive, you could achieve a crude PWM type output, from 0b00000001, 0b00000011, 0b00000111, 0b00001111, 0b00011111, 0b00111111, 0b01111111
7 levels.
Wouldn't be very bright unless you buffered its output, they likely have limited drive capability, have to check the datasheet on the chip on the board.
Once you stop sending, than what it receives is unknown.