X10 Firecracker

An X10 Firecracker is a trademarked name for a small RF transmitter that transmits home automation signals compatible with the X10 industry standard of receivers and switching devices.

The X10 Firecracker plugs into a 9-pin computer serial port, and includes a passthrough connector allowing that serial port to be used with other devices. The Firecracker is transmit-only, and therefore can only be used for sending home automation commands, and not receiving them. The Firecracker is powered by the serial port itself.

X10 home automation signals can be transmitted either by radio-frequency or over a powerline carrier (PLC), but usually can only be received by devices connected to the power line via PLC. Therefore, in order to use an X10 Firecracker to control power line devices, a receiver is required to convert the signal from RF to PLC.

On the computer, the programming specifications for the Firecracker are well published. The Firecracker is commanded by manipulating the RS232 status pins, namely RTS and DTR, and not through the data pins. Further, the Firecracker is responsive only when specifically-defined sequences of state changes are pulsed through these status pins. This allows the Firecracker to ignore commands meant for a device sent through to its pass-through port. Most standard serial devices ignore the rapid state transitions of the DTR and RTS pins used for commanding the Firecracker, particularly when no data is being sent over the data pins.

The Firecracker was originally sent out as part of a low-cost home automation promotional kit by X10 Wireless Technology. Although this device is very basic and lacks flexibility and programmability, its simplicity and low cost is attractive to computer programming hobbyists wishing to write computer software that can control external lights, bells, or appliances.