CIRCUIT
Circuit - LEDs
Main LED Strip (D2-11)
Each of the LEDs in the strip are connected
to an output on the CD4017 decade counter.
As the counter sends its outputs high when
on, and we want our LEDs to turn on one at a
time, we connect the outputs to the anodes of
the LEDs. The cathodes of the LEDs are con-
nected to GND via a current limiting resistor.
If we wanted all the LEDs to be on except the
one that is connected to the output that is
currently active, we can connect the outputs
to the cathodes of the LEDs. The anode can
then be connected to positive voltage through
a current limiting resistor.
Clock LED (D1)
To give some added visual feedback, we have
added an LED and current limiting resistor
to the clock signal coming from the 555 tim-
er. This is turned on when the clock signal
goes high.
Current Limiting Resistors (R3, R4)
These resistors limit the current going through
that part of the circuit. This protects the LEDs
from burning out. The higher the resistance
value, the lower the LED’s brightness and the
longer the LED will last.
Only one resistor is needed for the entire strip
of LEDs. This is because our circuit is de-
signed to turn one LED on at a time. If there
were more than one LED on at a time, then we
would need to use a resistor per LED.
To calculate the resistors minimum value, we
can use the following equation:
To find the voltage drop across the resistor, we
need to take the voltage drop across the LED
away from the total voltage from the supply.
Vsource is the maximum Voltage we will con-
nect to the circuit. This will be 16V in our case.
Vled can be found in the LEDs datasheet.
Check the datasheet link found in the BOM.
The LEDs used in this kit have a typical for-
ward voltage of 3.2V.
The current (I) will be the LED’s recommended
forward current. The datasheet states it’s max
forward current as 30mA. The value used in
the datasheets measuring conditions can be
used as a good safe current. This is stated
as 20mA.
(16 - 3.2) / 0.02 = 640Ω
640 is our minimum resistor value. After test-
ing the brightness of the LEDs with different
values above 640Ω, we settled on 2kΩ.
Check out the calculator on the
find the LEDs forward current when using a
2kΩ resistor.
R =
V
SOURCE
- V
LED
I
Summary of Contents for SABER CARD
Page 1: ...I N S T R U C T I O N M A N U A L SABER CARD v0 92...
Page 7: ...CIRCUIT Circuit Component Layout D2 R4 U2 D1 R1 R2 C1 C2 R3 U1 D3 D4 D5 D6 D7 D8 D9 D10 D11...
Page 13: ...ASSEMBLY D2 R4 U2 D1 R1 R2 C1 C2 R3 U1 D3 D4 D5 D6 D7 D8 D9 D10 D11...
Page 15: ...ASSEMBLY D2 R4 U2 D1 R1 R2 C1 C2 R3 U1 D3 D4 D5 D6 D7 D8 D9 D10 D11...
