Theory of Operation
The 51000-001 wireless CO detector is a low power wireless transmitter which is
intended to operate on a single fixed frequency of 345.000MHz. This device operates
from 3 volts DC, supplied by the Apollo CO detector CR123A battery.
The Apollo CO Detector has four status bits to indicate the status of the sensor assembly.
The device will send a status message via ASK data transmission on a frequency of
345.000MHz:
a)
At 70 minute intervals, for supervisory purposes to assure security system
integrity.
b)
When status changes to a fault condition for more than 5 seconds.
c)
When status changes to a restore condition
Refer to the schematic diagram and block diagram with the following description.
The processor, U1 runs on an internal oscillator which does not require an external
crystal or ceramic resonator. U1 monitors the state of the status inputs (pins 3 through 6
of J1). U1 also generates the codes sent to U2 using Manchester coding with a 50 % duty
cycle. All of the messages sent are by designed to be less than 10 mS of transmitter “on”
time in any 100mS period for power averaging purposes. If a), b), or c) (outlined above)
occurs, U1 will transmit ASK data via U2 as follows:
1.
The data line from pin 2 of U1, which is connected to pin 6 of U2, will toggle
high and then low. This will cause U2 to turn on and start its internal
10.78125 MHz crystal reference oscillator which is connected to crystal X1.
Within 200 to 300 uS of turning on, the 345.000MHz PLL synthesizer inside
U3 will be locked and stable.
2.
After the data line is held low for 500 uS as described above, and the PLL is
stable, U1 will then begin to send data to U2. When pin 6 of U2 goes high,
the 345.000MHz PA stage will be enabled and transmit RF from pin 4 of U2
until pin 6 of U2 is set low again by pin 5 of U1.
3.
When the data input pin 6 goes low, U2 will disable it’s PA section and stop
transmitting RF from pin4, but U2 will remain on and it’s PLL will remain
locked and ready to transmit when the data line goes high again.
4.
This process described in 2 and 3 above is repeated thorough each data
transmission.
5.
After the data transmission is completed, Pin 6 is held low. U2 will return to
the sleep mode 6.5 mS later.
6.
Steps 1 thru 5 will repeat as needed for additional packet transmissions.