First off, I am relatively new at tinkering with electronics, though I am not a dummy when it comes to programming and physics...
I purchased a DDS module (AD9850 BK009) (same as this:Purchase micro Module Now | ELECFREAKS). I followed this demo (DDS-AD9850 + Open oscilloscope - Lxardoscope - Blog) to connect the DDS module to an Arduino UNO. I set the frequency of the AD9850 to 0.5 Hz and inspected the output using the Arduino and the Lxardoscope software (I do not have my own oscilloscope at home). The output looked okay; the square wave output alternates between 0 and 9.951 V, and the sine wave output varies between 0.000 and 2.139 V. The square wave output lights an LED in the expected blinking fashion; the sine wave does nothing. I am assuming the reason is simply because 2.139 V is too low to power the LED. I have no specs on the LED, and the DDS module manual is in Chinese! If the problem is simply that the voltage is too low, do you have any suggestions on how to amplify the signal?
Ultimately, I want to move on and power a laser diode using the DDS module with a DC component of voltage supplied to the diode being in the middle of the excitation range for the diode, with a superimposed sine wave from the AD9850, such that the light intensity varies as a simple sine wave. Any suggestions on directions to go/components to use would be great.
You feed a led about 10V, how much resistor did that take? Or are you okay with short life leds?
The color of the led is tied to the threshold voltage (look it up, there will usually be some kind of approximate table) and after that you don't want much more. Only the tops of sine waves are safe for that.
Thanks for your reply.
Nice, I figured these LEDs were so cheap, their colors were determined by the plastic surrounding them rather than actual differences in semiconductor. Anyway, I switched from a yellow to a red LED, but still with no luck. I was using a 220 ohm resistor, but even with removing the resistor, I apparently did not have enough voltage.
Anyway, it looks like I really need to implement an amplifier...
A red LED should light up at about 1.8 to 2.1V
It could be that your sin output can not supply the current needed to light an LED.
Once again, Mike has nailed it.
Keep looking around, Analog Devices has the Datasheet for the AD9850, and the sine output supplies NOWHERE near enough current to meet the threshold of a LED. The sine output should feed a current amplifier, but you can use a load resistor to get the voltage up and use an audio op-amp to get voltage and reasonable current out (at the freq setting you specify). The output does not have a negative swing, but is offset above the 9850 supply (by about 250mV with no load).
Once you hit that threshold, I don't think that you want to raise the voltage much at all.
Over-voltage is not really an issue, as long as you keep current between threshold and Maximum, and do not exceed reverse breakdown voltage, of course. You can slap a LED across 110 main, as long as you have a current limiting resistor (a meg, or so?).
123Splat:
Over-voltage is not really an issue, as long as you keep current between threshold and Maximum, and do not exceed reverse breakdown voltage, of course. You can slap a LED across 110 main, as long as you have a current limiting resistor (a meg, or so?).
And maybe learn more about Ohm's Law and voltage drops.
Because when you have positive sine waves you can put in a proper value resistor for less than peak voltage and damage your led as voltage rises from there.
Smoke, I left out one important component, 1N4001.
I used that config as a continuity checker for years.
What you might try with MCU's is to read the analog sine with ADC and PWM the led to match.
PS my 5mW red laser diodes run through constant current circuits at 20mA 4.5V though I feed them 5V.
They can pulse insanely fast and a bag of 10 is less than $5 shipped.