Installing LED Indicator for RC Toy Car Help

Discussion in 'Technical Repair' started by zakmuh, Jul 25, 2016.

  1. zakmuh

    Thread Starter New Member

    Jul 25, 2016
    7
    0
    Hi Everyone,

    I'm a newcomer to this forum. Please put me in the right direction, if I've posted in a wring forum :)

    I don't have much electronic knowledge, but I can fix some stuff but inspection. I need some help with installing LED lights for my nephew's RC car. What I've got is a 4-way controlled Audi R8 toy car. The car needs 3 x 1.5v AA batteries and the controller needs 2 x 1.5v AAs. I bought LEDs (3v) from local Maplin and did some wiring work for LEDs to work like in real cars:
    1. Upon switching on, front white (x 2) and rear red (x 4) LEDs come on - direct connection from batteries
    2. When reversing, one white LED at rear centre comes on - rear motor
    3. When 'trun' button pressed (left or right) on the controller, flashing LEDs (font and rear) comes on - connection from front steering motor

    All the connections work fine, however, when the car is operating (moving) the battery power is not enough (LEDs consuming too much power?), especially the flashing LEDs (indicator) not bright enough.

    My question is....I want use a 9V battery to power up only the LEDs, but get the signal from the front steering motor connection?

    Any help on this highly appreciated.

    Car : http://www.argos.co.uk/static/Product/partNumber/9143937.htm

    Wire connections : https://postimg.org/image/dt5mlvtvf/

    Some videos:



    Cheers
     
  2. zakmuh

    Thread Starter New Member

    Jul 25, 2016
    7
    0
    I just found out that I should've connected each LED through a resistor. Is the purpose of the resistor to stop LED draining the battery?
     
  3. #12

    Expert

    Nov 30, 2010
    16,248
    6,745
    The purpose of the resistor is to stop the LED from blowing up. An LED is not a light bulb. It doesn't have any ability to limit current. Attaching an LED directly across a battery is like connecting a fuse across a battery. The only thing that's going to happen is a blown fuse or a blown LED.
     
    zakmuh likes this.
  4. zakmuh

    Thread Starter New Member

    Jul 25, 2016
    7
    0
    Thanks for your clear and concise explanation Expert :)

    Anyone on using a 9v battery for indicators?
     
  5. #12

    Expert

    Nov 30, 2010
    16,248
    6,745
    LEDs have different voltage needs ranging from about 2.1 volts for red to about 3.2v to 4 volts for blue or white. What you do is divide the leftover voltage by the current required to find the resistor value. So, 9v-3.2v = 5.8 v leftover. 5.8v/0.02 amps = 290 ohms.
    Because 20 ma is the max for your standard LEDs, you raise the resistance to the next higher available value, 330 ohms for blue or white.
    For red, 6.9V/0.02A = 345 ohms and the next popular value of resistor is 390 ohms.
    There is no law that says you must run LEDs at their highest survivable voltage, and the work pretty well down to half power, so a handful of 390 ohm resistors should meet your needs and keep the LEDs surviving a long and healthy life.

    ps, just got promoted to, "expert". Don't know how that happened.:confused:
    signed,
    Number Twelve
     
    zakmuh likes this.
  6. zakmuh

    Thread Starter New Member

    Jul 25, 2016
    7
    0
    Nice one mate

    Cheers
     
Loading...