I agree partialy

The led in the opto is drawn reversed
diagram with external led is

pic pin--------[Resistor]---->|------>|-------gnd

current depending on optocoupler probably around 10 ma
however , forward drop in led's is generally between 1.5 and 1.7 volt (at
currents of a few ma)
for a 5 volt supply of the pic we have on the resistor 5-1.5-1.5=2 volt this
gives an r of 2/0.01=200 ohm

Be aware that with a single transistor optoisolator the ratio between input
and output current (current transfer ratio) is usually less than 100% (you
send more current in than you can switch).

What I would do is test your camera by wiring a resistor in series with a
switch on the shutter input and checking with how high of a value resistor
the camera reliably snaps a picture, then measure the current thru the
resistor so you have an idea about what you need. start with 1 kohm or so
and keep halving it down 5k,2k2,1k5 etc in subsequential steps.

Kind regards
Peter van Hoof

----- Original Message -----
From: "Robert Monsen" <rcmonsen@COMCAST.NET>
To: <PICLIST@MITVMA.MIT.EDU>
Sent: Wednesday, July 14, 2004 2:39 AM
Subject: Re: [EE:] Rocket timer


> ----- Original Message -----
> From: "Mike" <mrgizmo@VIANET.CA>
> To: <PICLIST@MITVMA.MIT.EDU>
> Sent: Wednesday, July 14, 2004 1:02 AM
> Subject: Re: [EE:] Rocket timer
>
>
> >   I redesigned the schematic, but I'm not sure if the opto is hooked up
> > properly, that is just a general opto, I will be using a better one.
Also
> if
> > I put a series red led(I have multiple sizes) wat voltage drop should I
> > expect across it.
> >
> >
> > http://www.angelfire.com/mech/homerov/rocket/schem.jpg
> >
> > --
> > http://www.piclist.com hint: To leave the PICList
> > mailto:piclist-unsubscribe-request@mitvma.mit.edu
>
> Optoisolators work by passing current through the LED. Thus, the left side
> is upside down in your picture, the diode should be facing downwards.
>
> The voltage drop across it is going to be something like 0.7V on the left
> side, and something like 0.2V on the right side (unless you use a
> darlington)
>
> Look up the datasheet of the optoisolator you decide on, and make sure the
> resistor is sized appropriately to give it enough current to saturate the
> transistor in the opto. If you use a darlington opto, that will be easier,
> but it'll have a bigger voltage drop on the output side, maybe 1V.
>
> One thing is that you've added pullups to GP0 and GP1; you don't need them
> if you turn on the 'weak internal pullups' in your initialization code.
>
> Finally, you need some caps around that regulator. Look at the datasheet
for
> the 7805; you see that it needs at least a 0.1uF cap on the output for
> stability and transient response. If you are running your solenoid off of
> the same 9V battery, you will also need an input cap of something like
> 0.33uF.
>
> Regards,
>  Bob Monsen
>
> --
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> mailto:piclist-unsubscribe-request@mitvma.mit.edu
>

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