# Does the 433 MHz transmitter/receiver, transmit the voltage?

The title, says it all...

I would like to know if the 433 MHz transmitter/receiver (couldn't find a datasheet, here is all I found on it) transmits the voltage, or if it just a logic output of '1' or '0'?

For example, if I send through the data pin on the transmitter a current of let's say 2.5V, does the receiver connected to a circuit of 5V, output 5V or 2.5V through the data pin?

I think it would logically output 5V but I am not sure...

Disclaimer: I have no components, I just bought some basic components and an Arduino kit on Amazon. But I am so impatient and excited to get the parts that I already started drawing up some circuits. So beware, a lot I am saying may be wrong...

• It is clearly stating that it s using ASK (Amplitude shift keying) modulation. Also it is stating that the transmission rate is in Kbps, which is a big hint on the type of the data transmitted. From here you can google on. – Eugene Sh. Sep 23 at 18:23
• @Eugene Sh. Oh sorry, didn't know it had anything to do with this. Thanks :) Will Google and see. Thanks again! – FireGreeks Sep 23 at 18:25

These 433 MHz transmitters use OOK modulation (also called ASK), making the transmitted signal look like:

So the transmitter is simply switched on (1) or off (0).

Most 433 MHz receivers will "filter out" the 433 MHz so we're left with the blue signal.

When no signal is received for some time, most receivers will try to decode a signal from the noise they receive and the noise from the receiver itself. That then results in a random 0 / 1 pattern.

To do something useful with this system that random signal must be ignored and the useful signals must be extracted out. This is a typical job for some software on a microcontroller. You also want a microcontroller on the transmitter side. Then it is easy to create long 0 /1 sequences like: 0010100100111010101101

When you transmit that code, the microcontroller will respond and that will open your garage door while the noise doesn't open the door. Also your neighbor's door will use a different code so the two doors will not interfere even though you would both be using 433 MHz.

No, the transmitter's data pin isn't interpreted as a voltage, but as a zero or one logical signal....binary data.
Similarly, the receiver's data pin is a logic signal. It will swing from ground (logic zero) to Vcc (logic one).

You might think that such a transmission system is similar to a UART function. You might actually get it to work this way, but there are some subtle problems that you may have to overcome...

• A UART includes a start bit, then transmits a byte serially, and ends with a stop bit. The start bit must activate the transmitter if you hope to receive the first byte. The stop bit would turn off the transmitter, and it would remain off until you transmit the next byte. So you may have to logically invert the UART's serial data.

• When a transmitter is not active for awhile, the receiver looks for a very weak signal, and occasionally thinks a signal is present even if the transmitter is off...you get bogus data. Software must deal with this condition.

• A receiver looking for a very weak signal may be "startled" by a very strong signal from a nearby transmitter. While the receiver adjusts to the strong signal, you may get bogus data, or data pulses whose timing is altered. An example of this might be a start-bit that gets stretched in time, fouling the first data byte transmitted.

• UART protocol can work well, and is recommended. You might try slower data rates like 1200 baud, before trying higher speed. Other serial protocols can work too: Manchester encoding of data is excellent. You can also transmit pulse-width-modulated (PWM) serial stream too, as long as its frequency fits within the data rate.