ZIO, Motherboard User Manual
Rev. 2.0
Zilogic Systems
Page 8
Chapter 3. ZIO Recipes
1. GPIO Port
Connecting LEDs.
Connect the anode of the LED to an
Output
signal, and the cathode to GND.
The built-in series resistor is sufficient to limit the current.
Connecting series of LEDs.
Since the
Output
signal can not provide sufficient power for more
than one LED, and external power source is to be used. And the power supply can be controlled
using a MOSFET switch.
The circuit diagram for connecting a series of LEDs is shown above. The following formula can
be used to calculate the resistance for the current limiting resistor. (The voltage drop across the
MOSFET is considered to be negligible.)
R = (V
cc
- NV
d
) / I
d
Where,
V
d
Voltage Drop Across LED
N
No. of LEDs
I
d
Current for the required brightness
V
cc
LED supply voltage
R
Current Limiting Resistor
As an example, for the following parameters,
• V
cc
= 12V
• I
d
= 11mA
• N = 4
the calculated current limiting resistance is 470 ohms.
