Passive Infrared Sensor


Part of my journey through Shenzhen I/O

Problem: time is a simple input connected to a clock that provides the current time. on-time and off-time are XBus inputs that specify the time at which the alarm should be enabled and disabled, respectively. sensor is a simple input that indicates the level of infrared detected. alarm is a simple output that enables the alarm when 100 is sent to it. If the alarm is enabled and the sensor detects a value of 20 or higher, the alarm should be enabled.

This one was tricky because of the number of inputs. My strategy was to to use a MC6000 to determine whether the system is armed or not.

  • p1 is connected to time to provide the current time.
  • x1 is connected to on-time
  • x2 is connected to off-time
  • x3 is connected to the downstream chip that looks at the sensor and triggers the alarm.

To detect whether the system is armed, it stores 100 in acc when the current time matches on-time, and stores 0 in acc when the current time matches the off-time. It then moves the value of acc to x3 for consumption downstream.

  teq p1 x1
+ mov 100 acc
  teq p1 x2
+ mov 0 acc
  mov acc x3
  slp 1

The logic to trip the alarm reads this value from x0, and looks at p0 for the value of sensor, and outputs the alarm state to p1, which is connected to alarm.

  teq x0 100
- mov 0 p1
- slp 1
- jmp loop
+ tgt p0 19
+ mov 100 p1
- mov 0 p1
  slp 1

Cost is ¥8, power usage is 481, and 14 lines of code are necessary.