300ma LED Strobe Light

Moonwizard

Good day to all!

I want to build a strobe light of sorts using a single LED to start and adding more as I learn.· Then maybe progressing to PWM output.

1. Using logic level N-Channel MOSFETS (2n7000), what would be a good circuit to use to:
·· A. Protect the port on the propeller.
·· B. Provide the proper forward current to the LED.

2. What might be a good way to "Strobe" the LED in SPIN?
·· A. Programmable on time.
·· B. Programmable off time.

I've looked at the following circuit:

I arrive at the 6.8ohm resistor using: .3ma / ((3.2VDC * 1)- 5VDC)

The 1k resistor is something I've seen using the PIC chip.·

                        -----------LED---6.8ohm------5VDC
pplr             mosfet |
---              ---------------
   |             |    Drain    | 
   |             |             |
P2 |---1k--------|Gate         |
   |             |             |
   |             |   Source    |
---              ---------------
                        |
                       GND

---

SPIN code idea

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{Obvious code Here}
repeat
··· !outa[noparse][[/noparse]Pin]······· 'toggle the port
··· waitcnt(clkfreq / 1000 * DelayMS2 + cnt)···· 'wait using an independent·"on time"
··· !outa[noparse][[/noparse]Pin]······· 'toggle the port
··· waitcnt(clkfreq / 1000 * DelayMS + cnt)····· 'wait using an independent·"off time"

---

SPIN code idea

---

Thank you for your indulgence!



Post Edited (Moonwizard) : 10/4/2007 3:07:02 AM GMT

deSilva

If you add [noparse][[/noparse] code ] and [noparse][[/noparse] /code ] tags it will look much better, as a fixed space font will be used. You can edit your posting!

300mA is not so much you could not use any standard bipolar power transistor (beta = 30, so the Prop has to drive with 10 mA, needing a base resistor of 220 to 330 Ohms)...

BTW: The forward voltage of a 300mA LED should be much more than 1V8...

Post Edited (deSilva) : 10/4/2007 3:05:10 AM GMT