User's Manual

GL865 Hardware User Guide
1vv0300910 Rev.1 – 2011-07-22
Reproduction forbidden without Telit Communications S.p.A. written authorization - All Rights Reserved
page 61 of 79
Because resonance frequency depends on acoustic design, by
lowering the amplitude of the driving signal the response
bandwidth tends to become narrow, and vice versa.
Summarizing: V
pp
↑  f
o
↓ V
pp
↓ f
o
↑
The risk is that the f
o
could easily fall outside of new
bandwidth; consequently the SPL could be much lower than the
expected.
11.7.3. Working Current Influence
In the component data sheet you will find the value of MAX
CURRENT: this represents the maximum average current that can
flow at nominal voltage without current limitation. In other
words it is not the peak current, which could be twice or three
times higher. If driving circuitry does not support these peak
values, the SPL will never reach the declared level or the
oscillations will stop.
11.8. STAT LED Indication of network service
availability
The STAT_LED pin status shows information on the network service
availability and Call status. In the GL865 modules, the STAT_LED
usually needs an external transistor to drive an external LED.
Therefore, the status indicated in the following table is
reversed with respect to the pin status. The AT command to
enable the function is AT#SLED=2, in order to save the function
use the AT command AT#SLEDSAV, the AT command AT#SLED=0 disable
the function and the functionality of GPIO8 can be used. (see AT
Command user guide)
WARNING:
It is very important to respect the sense of the applied
voltage: never apply to the "-" pin
a voltage more positive than
the "+" pin
: if this happens, the diaphragm vibrates in the
opposite direction with a high pr
obability to be expelled from
its physical position. This damages the device permanently.