The stairlift system consists of at least three separate PCB’s: the main controller, the display (with remote receiver), and the remote control. Each PCB has a microcontroller with its own firmware program written by us. Dena Technologies was not involved in the mechanical design.
The controller is the core of the system and performs most of the functions. It has an H-bridge MOSFET driver capable of controlling the speed and direction of a 20A 24V DC motor. A safety brake is engaged by default unless released by the controller. The controller also monitors and controls the charging of the on-board battery. Several limit switches are monitored continuously for safety to stop the chair in the event of an impact or end of the track or if there is a fault.
Prototypes were built and we debugged the firmware on a demonstration setup at the client site. The firmware has a sophisticated method of controlling speed on staircases with curves in them.
The stairlift system was designed so that additional modules could be chained to the controller and the display is the first module. The stairlift display is a fairly generic module with a character LCD display and IR remote control receiver.
It uses a one-wire half-duplex RS232 signal to receive text to display from the controller and responds with any remote codes which may have been received.
The stairlift remote control is also a fairly generic module, powered by two AAA batteries, which can output an IR signal with up to 20 meters range (three flights of stairs). It uses a conventional IR remote code typically used for television and other devices.
A set of jumpers on the remote allows the user to change to a different prefix code to avoid interference with other devices. The main controller has a menu option to match the prefix code since the display is required in order to receive the remote signal.
An encoder was designed to measure the speed of the motor, but the client changed the motor which required a different encoder. Some difficulties were presented by the encoder in the new motor, but these were resolved by providing feedback to the motor manufacturer.
A simplified version of the motor controller was designed, but development is on hold while the first controller production gets under way.
Additional modules are planned such as a control for a powered lift gate to pass doorways on intervening floors.
These circuit boards are being manufactured overseas to control cost.