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Several other questions are posted about methods for flashing an LED, but one additional requirement I have is the ability to turn the circuit on or off with a micro controller (Netduino, 3.3v). This schematic is very close. What changes would be necessary to achieve 38.5kHz? Also, how could I make an additional adjustment to start or stop the circuit via a pin on the Netduino? |
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You can tweak the frequency with the 5k potmeter. I think you can get a pretty good range with that. If it's not enough, you could probably change the other resistor to something or a little larger value so the frequency drops. To make it possible to switch the LEDs on and off I would probably a transistor (or a MOSFET) after the two leds. You could then connect the base or gate to your netduino with a 1k resistor or so. It doesn't start/stop the circuit, but it does start/stop the LEDs which I think is the result you want to go after. |
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If you're using Netduino, maybe you can drop the 555 circuit and use software temporization. Here (http://www.netduino.com/projects/) we have two tutorials on how to blink the led and also how to turn it on and off using a button. You will just need to attach the infrared led to an I/O port and map it in the software. |
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Since you have a microcontroller around for switching the signal on and off it makes sense to let it do the dirty work as well. I'm not acquainted with Netduino, but I see that it's an ARM7 running at 48MHz, which makes it more than powerful enough for this. Set a timer to a 13\$\mu\$s period, and let it toggle an I/O pin on each timeout. The signal's period is then 26\$\mu\$s, giving a frequency of 38.5kHz with only 0.1% error. Duty cycle will be 50%. |
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