Calculations of the low filter, Recommended characteristics for the buzzer, On/~off signal – Sierra Wireless WISMO218 User Manual
Page 66: Figure 29, Example of led driven by the buzzer output
WA_DEV_W218_PTS_002
Rev 005
Page 66 of 109
Product Technical Specification &
Customer Design Guidelines
Calculations of the Low Filter:
Req is the total resistor in line.
C is the capacitive charge on T1 and the ground.
The cut-off frequency (Fc) must be higher than FBUZZ-OUT.
Due to the conception of this signal, the frequency modulation of the BUZZER signal is 64* FBUZZ-
OUT.
Fc must be at least 64 * FBUZZ-OUT.
Fc = 1/ (2. .Req.C)
Recommended characteristics for the buzzer
Electro-magnetic type
Impedance: 7 to 30
Sensitivity: 90 dB SPL min @ 10 cm
Current: 60 to 90mA
The BUZZER output can also be used to drive a LED as shown in the figure below:
Figure 29. Example of LED Driven by the BUZZER Output
The value of R607 can be harmonized depending on the LED (D605) characteristics.
The recommended digital transistor to use for T601 is the DTC144EE from ROHM.