B. Expansion module interface circuit design
Expansion module circuit in system is mainly responsible
for collecting sensor alarm signal, and sending the
information through RS232 to Liod platform that processes
this information. Meanwhile, extension module receives
control command of appliances from the Liod platform and
achieves control of household appliances.
1) Sensor interface circuit
Smoke, gas leak and infrared sensor alarm signals access
to P2 port of the singlechip by photoelectric coupling. When
no alarm in sensor, photoelectric coupling chip is in the off
state, and the singlechip ports connected to it are low level;
When sensor has alarm, sensor output is high level, right
now the photoelectric coupling chip is on, and conterminous
singlechip port is of high level. The singlechip collects and
makes the corresponding processing with alarm signal.
2) Appliances control interface circuit
Household appliances control interface circuit uses relay
K1 ~ K4, which respectively control four road of home
appliance closed or disconnected. Q1 ~Q3 are relay coil
current drive, the P1 port of singlechip controls circuit. DD1
~ DD4 LEDS display one way of control circuit working
condition, mainly in order to debug circuit Settings.
3) RS232 interface circuit
Expansion module communicated with Liod platform by
RS232 interface, RS232 level conversion chip of expansion
board adopted MAX232, and it’s master processor chips is
the general used MCS-51 single-chip .[4]