P14/54 T-SM47j
3.2.2 Handset overview
There are two versions of handset, a cordless type (infrared
handset) with an infrared emitter powered by 2 AA cells
and a corded version (corded handset) with an RS232 link
to the main processor on the ‘4 actuator PCA’. The latter
version derives its power from the T20-a.
3.2.2.1 Infrared handset
The 4 x 5 matrix keyboard is decoded using a proprietary
keyboard decoder. This device is powered down and
remains dormant until a key is pressed causing its clock
oscillator to be initialised. The key is decoded and the 38kHz
modulated signal is fed to the infrared LED via a FET. The
whole system is powered via 2 AA batteries
3.2.2.2 Corded handset
The 4 x 5 matrix keyboard is decoded using a proprietary
keyboard decoder. This device is powered down and
remains dormant until a key is pressed causing its clock
oscillator to be initialised. The key is decoded and the 38kHz
modulated signal is fed to a PIC processor. The processor
decodes the output from the keyboard decoder into RS232.
This output is fed to an RS232 line driver. The corded
handset’s power is supplied directly from the T20-a, 5V
power supply. The handset contains a DC-DC converter to
supply 3.3V for the keyboard decoder. There are indicator
LED’s to show the charge status of the table batteries (main
and standby).
To Next Page
Loading...
