NLMD
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Saw this on another forum, thought you guys might be interested.
For those who are interested in making your own brake lights (works for reverse, too), here is a short walkthrough. If you like images, I'm sorry in advance, this will be just a text description
1. Get a small, unused servo.
2. Open the servo, desolder the motor, remove gearing.
3. Get a multimeter and make sure that potentiometer is in neutral. That means that output current from wires (desoldered from motor) is 0 or slightly minus.
4. Solder new wires to + and - where the motor was.
5. Apply full brake and measure the output voltage. If you see minus voltage, reverse the cables.
6. Use resistors with appropriate Ohms if needed.
7. Solder the LEDs to the end of cables, that's it.
Ad 6)
Use the Ohm's law (Wiki). In simple words, the voltage going to LEDs must not burn them. Say that the maximum voltage for LED you bought is 2.1V. Output voltage coming from servo is 4.2V.
Ohm's law says I=V/R => R = V/I. R is the resistance you need to know before buying resistors. Resistors are actually "consuming" the added voltage amount you don't need. 4.2V minus 2.1V is 2.1V again. So you need a resistor, that will "eat" 2.1V and drop the voltage to 2.1V. As per the Ohm's law, it is voltage divided by current. Voltage is 2.1V. Current is usually 20 mA for normal LEDs. But you can't mix different values like kilo, mega, tera... therefore 20 mA = 0,02A. 2.1V/0,02A => 105 Ohm resistor. 100 should handle it, but to be on the safe side, buy 110.
This works the same way for normal head & tail lights. All you need to do is to calculate the resistor value. I'll elaborate again to show en example. Output from ESC is 4.8V. You just bought a LED that is running on 3.3V. Difference in voltage is 1.5V. LED is consuming 20mA. 1.5/0,02 = 75 Ohms. Therefore you will need a 75 Ohm resistor to solder on the positive wire before it reaches LED.
If you connect the LEDs in parallell, each and every LED must have a resistor before the positive cable reaches it. If you connect the LEDs in a series, it might happen you don't need a resistor at all. This happened to me, I was just lucky. 2 LEDs where one consumes 2.1V makes together 4.2V. Output from servo in maximum brake position is 4.2V (my servo), so it is completely equal and there is no need for a resistor.
Hope this helps, here is a short video of my new brake lights:
http://www.youtube.com/watch?v=isIPGpTPOBs
For those who are interested in making your own brake lights (works for reverse, too), here is a short walkthrough. If you like images, I'm sorry in advance, this will be just a text description
1. Get a small, unused servo.
2. Open the servo, desolder the motor, remove gearing.
3. Get a multimeter and make sure that potentiometer is in neutral. That means that output current from wires (desoldered from motor) is 0 or slightly minus.
4. Solder new wires to + and - where the motor was.
5. Apply full brake and measure the output voltage. If you see minus voltage, reverse the cables.
6. Use resistors with appropriate Ohms if needed.
7. Solder the LEDs to the end of cables, that's it.
Ad 6)
Use the Ohm's law (Wiki). In simple words, the voltage going to LEDs must not burn them. Say that the maximum voltage for LED you bought is 2.1V. Output voltage coming from servo is 4.2V.
Ohm's law says I=V/R => R = V/I. R is the resistance you need to know before buying resistors. Resistors are actually "consuming" the added voltage amount you don't need. 4.2V minus 2.1V is 2.1V again. So you need a resistor, that will "eat" 2.1V and drop the voltage to 2.1V. As per the Ohm's law, it is voltage divided by current. Voltage is 2.1V. Current is usually 20 mA for normal LEDs. But you can't mix different values like kilo, mega, tera... therefore 20 mA = 0,02A. 2.1V/0,02A => 105 Ohm resistor. 100 should handle it, but to be on the safe side, buy 110.
This works the same way for normal head & tail lights. All you need to do is to calculate the resistor value. I'll elaborate again to show en example. Output from ESC is 4.8V. You just bought a LED that is running on 3.3V. Difference in voltage is 1.5V. LED is consuming 20mA. 1.5/0,02 = 75 Ohms. Therefore you will need a 75 Ohm resistor to solder on the positive wire before it reaches LED.
If you connect the LEDs in parallell, each and every LED must have a resistor before the positive cable reaches it. If you connect the LEDs in a series, it might happen you don't need a resistor at all. This happened to me, I was just lucky. 2 LEDs where one consumes 2.1V makes together 4.2V. Output from servo in maximum brake position is 4.2V (my servo), so it is completely equal and there is no need for a resistor.
Hope this helps, here is a short video of my new brake lights:
http://www.youtube.com/watch?v=isIPGpTPOBs
