BT900 Development Kit
Version 0.3
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To prepare the board for current measurement, cut the shorting of the solder bridge SB9. After this modification
there are two primary ways to measure the current consumption:
Using Ammeter – Connect an ampere meter between the two pins of connector CON1. This monitors the
current directly.
Using Oscilloscope (Note1) – Mount a resistor on the footprint R28. The resistor should not be larger than 10
Ohm. Connect an oscilloscope or similar with two probes on the pin on the CON1 connector and measure the
voltage drop. The voltage drop is proportional with current consumption. If a 1 Ohm resistor is chosen, 1 mV
equals 1 mA.
There is also a third way to measure current:
Using Current Shunt Monitor – The current drawn by the BT900 module can be monitored using the Current
Shunt Monitor (CSM), INA216A3YFFR, TI (U8). The gain of INA216 is 100 V/V for lowest possible drop voltage.
Note: The Using Current Shunt Monitor method allows the dynamic current consumption waveforms on
oscilloscope as the BT900 radio operates. This can provide insight into power optimization. The
accuracy of the CSM circuit drops when measuring currents down towards 200uA value.
Current consumed by the BT900 module is measured as a voltage (proportional to the current) using the CSM by
connecting measuring voltmeter OR oscilloscope to TP14 Connect measuring voltmeter or oscilloscope GND to TP15.
I(mA) = Vmeas_TP14(mV) /25.5
CAUTION: Take care not to short TP14 (the Current Shunt Monitor IC (U8)) output to GND, as that will
permanently damage the IC U8.
Note on CON1: CON1 is used for current measurement only.
