16
10.
Measuring
Resistance
When measuring resistance both the external load resistor as well as the 1 ohm sense resistor
built into the circuit board must be taken into consideration.
Example 1:
The illustration below shows a 10 ohm load resistor placed across one set of the OUTPUT
terminals. The total resistance is really 11 ohms (10 ohm load resi 1 ohm sense
resistance). While the fuel cell is shown as the power source, a battery, solar panel or wind
turbine can also be substituted.
The equivalent circuit is shown below:
Microprocessor
1 ohm
sense
resistor
INPUT
OUTPUT
USB
Connector
+5V
GND
Voltage
LED
Current
LED
O
H
ME
A
10 ohm
Load
resistor
1 ohm
sense
resistor
10 ohm
Load
resistor
= 11 ohms total
