Velleman-projects K8025 Assembly instructions Manuel d'utilisateur télécharger pdf (Page 4)

-5-

Supplyvoltage(V)-ledvoltage(V)

requiredcurrent(A)

=seriesresistance(ohms)

required current (A)

= series resistance (ohms)

Required resistor power handling=

voltage over resistor x current passed trough resistor

9V-1.7V

0.005A

=1460ohm

9V-(3x1.7V)

0.005A

=780ohm

(9V - 1.7V) x 0.005A = 0.036W

closest value :

use a 1k5 resistor

use an

820 ohm resistor

a standard 1/4W resistor

will do the job

Supply voltage (V) - (number of leds x led voltage (V))

How to Calculate the series resistor:

Example: operate a red led (1.7V) on a 9Vdc source.

Required led current for full brightness: 5mA (this can be found in the datasheet of the led)

LEDs in series:

Example: 3 x red led (1.7V) on 9V battery

Required led current for full brightness: 5mA

(this can be found in the datasheet of the led)

Ledsfeatureaspecicvoltage

drop,dependingontypeand

colour.Checkthedatasheetfor

exactvoltagedropandrated

current!

Neverconnectledsinparallel

Leds and how to use them

Anopencollectoroutputcanbecomparedtoaswitchwhichswitchesto

groundwhenoperated

Example:HowtoswitchanLEDbymeansofanopencollectoroutput

open collector outputs

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Velleman-projects K8025 Assembly instructions Manuel d'utilisateur Page 4