----- Original Message -----
Sent: Sunday, July 02, 2006 9:01
PM
Subject: [FlyRotary] Re: EM-2 question
for Tracy
I have an LED (designed for 12V)
wired up for the alarm light, and it comes on (not flashing, steady)
at what seems to be about half brightness when power is applied to the
EM-2.
Hi Bill,
I had the exact same problem with the current EM-2
(all in one), but not with the earlier one (separate electronics box).
In both cases, I used the exact same super bright LED's from the Shack
of Rat.
In talking to Tracy, my understanding is that the
alarm signal pin is on a 5V pull up, with a 10k ohm resistor. When the
EM-2 wants the light on, it grounds the pin, but when it's "off", the pin
would be sitting at 5V. If you tie the light to 12V, then there's a 7V
potential across the light, with a 10k ohm resistor in series. This
will allow some current to flow, and would probably not be noticeable on an
incandescent lamp, but for LED's, it will appear to be on, but
dim.
The fix was to use one of the EM-2 5V outputs for
the LED alarm light power. This gives no voltage
differential when the light is supposed to be off, and 5V differential
when on.
If you are using a pre-packaged LED that's made for
12V, and you use 5V instead, it will work but will be dimmer
than it would have been with 12V. You may have to use a
different LED.
Tracy may also have a better answer now, so stand
by for the real answer :-)
Cheers,
Rusty (single rotor engine currently installed on
the hanger
floor)