ASK

Amplitude Key Shifting is an inexpensive, and easy-to-implement method of transmitting data and control signals. In its simplest form, the sending module transmits a signal that once decoded toggles the output of the decoder chip. In a more advanced usage application, text may also be transmitted.

These modules work in a transmitter-receiver pair and use a technique known as Amplitude Shift Keying (ASK) to send data over radio frequency signals. The amplitude (i.e., the level) of the carrier wave (in our case, a 433MHz signal) is changed in response to the incoming data signal in Amplitude Shift Keying.

There are two frequencies at which the ASK modules operate, namely 333MHz and 433MHZ. When pairing the devices, the important requirement is that they operate at the same frequency, and they must be situated within the transmission / receive range of the devices.

The ASK modules provide the communications medium, however, the message must still be formulated and sent. In the past, two HT12 chips were used, one to send the signal and one to decode it; the HT12E and the HT12D respectively. The HT12 E would provide a parallel data input which is serialised for transmission. Once the signal is received and matched to the parallel input from the decider chip, the action can be taken.

In a more modern context, a microcontroller replaces the HT12s, but still performs the same function.

Shown below is an example pair of ASK devices that provide a one-way link between a sending PCB and a receiving PCB.