Knock Sensor light?

[steve ravet]

Since it's called a 12V LED it probably already has a current limiting
resistor built into it.  In that case, use it as is, and delete the 390
ohm resistor from the schematic.  Is there a resistor physically
attached to one leg of the LED?

Too much resistance means a dim LED.  Too little means a blown up LED. 
If it does blow up, get another one that's not for any particular
voltage, and use the circuit as is (with the 390 ohm resistor).

FYI the 555 output will be about 1.5 volts below the voltage used as
power, given a 25ma load on the output (according to the NS datasheet). 
In this case if the power is 13.5 then the output will be right at 12

--steve

Rex Weatherford wrote:
> I tried to pick up parts for this project today..  I did really good except
> for the L1 LED.  It does not list a voltage so I had to pick one..  (The
> Radio Shack SKU was too old..)
> 
> I choose a 12V LED.  Will that work?  Sorry I'm not really good with the
> voltages and I'm not sure how the timer effects that.  I assume that I did
> the right thing..???  I wasn't sure if the voltage coming through was 5V or
> 12V.
> 
> Thanks!
> 
> Rex

-- 
Steve Ravet
steve.ravet at arm.com
ARM,Inc.
www.arm.com
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