Pwm driven leds?

Hi I’m a total noob wondering if I could use the sequencer to drive a led light show at the same time as driving the servos. If so how would I go about hooking up the led? (which 2 pins of ground, vs and signal) + would I still need a resistor or could I address that issue by setting the limits in the scc sequencer. Sorry for the dumb questions , I’m an art student, not an engineer :wink:

The PWM generated for servos is not 0 to 100% like you might think. It’s a custom servo control methodology based on 1.0 to 2.0mS on and 20mS off. To control LED’s I would recommend you get the cheapest piece of crap servo available. Rip the board out of it. The servo is still a good gear head motor, so don’t toss it out. :wink: The board can be used to control two LED’s. Pulses over 1.5mS would drive one LED, and pulses lower than 1.5mS would control the other LED. The farther from 1.5mS would equal brighter light. You would still need the resistor…

Yeah, don’t forget that resistor I have lost many a led because of I forgot to put a resistor in! As a general rule when dealing with 5v a 1k resistor will do the job nicely. :smiley:

"…get the cheapest piece of crap servo available.Rip the board out"…this part I get :slight_smile:
With regards to how I might hook one led to the board, seems like put the the 1k resistor and led across the leads once occupied by the motor, I’m totally lost on the second led… Could you draw me a picture?( i mentioned the art student thing right? I’m kinda visual) … maybe one could build little lighting instruments that can be powered by servo pulses and the sequencer, like puppet size theatre instruments. I’m babbling…gonna stop now, thanks for your replies you guys

Here is a picture. Note that one short and one long lead are connected from the two LEDS to each side of the motor leads. This is what makes them operate independently, depending on whether the pulse is less than or greater than 1.5ms.

Example.jpg

Um, well… More like this.

srvled01.gif

Cool! thanks you guys! I’ll try it out tonight!
-Werner

The proper way to implement this is to set the servo board to 1000uS, measure the voltage, find which LED would be forward biased and calculate the resistor value for that LED. Then set it to 2000uS, measure the voltage, find which LED would be forward biased and calculate the resistor value for that LED. Now you should be able to control the brightness of the LEDs with servo values. There are many internet sources for calculating resistor values for LED’s.

Duty cycle would be quite low, < 20%. Of course you can over drive (pulse) the LEDs for greater output. Just don’t let them stay on with no servo refresh!

Alan KM6VV

No, the duty cycle will be from 0% to 100% depending on the pulse value sent. The frequency of the pulses will be 50hz, which can cause LED flicker if you move it quickly. But it can be easily filtered out with a small cap. I’ve tested it today. It works very well.

Then I’m not following you:

You said previously:

Which is a contradiction. Has something changed? He’s still using the SSC-32?

Alan KM6VV

Sigh…

The PWM generated for servos. As opposed to PWM generated by the servo. :wink:

Still not following, servos don’t generate PWM.

Alan KM6VV

Really? What makes the motor go round and round? Same thing that makes an LED go bright and dim. PWM… :smiley:

The servo receives pulses. Not PWM but PLM or pulse length modulation. This is where I say it’s not PWM, and explain why. But the servo board does indeed create PWM from the signal it receives to position the motor, or illuminate an LED.