Re: Newbee: Optocoupler to BasicStamp

This photo transistor does have 3 legs.
I will try your circuit tomorrow, so tired cant focus to even write this
post.

I will report back after trying it.

Thanks :-)

"John Popelish" <jpopelish@xxxxxxxx> wrote in message
news:LYudnatcOsiyRNjenZ2dnUVZ_tCdnZ2d@xxxxxxxxxxxxxxx
> Sam wrote:
> > I just ordered some 4N28s. While I am waiting for them to arrive I
thought I
> > would play around a bit.
> > I just cracked open a mouse and removed the photo transistors, but cant
get
> > the circuit to work.
> >
> > I have the center leg (base?) going to the input on my Stamp it is also
> > pulled up by a 10K resistor.
> > I have tried grounding both (not at the same time) other legs of the
photo
> > transistor, straight to ground and also through various resistors.
> >
> > I cant get the Stamp to detect on/off states. Any suggestions on where
my
> > circuit went wrong?
>
>
> For most sensitivity, you leave the base unconnected, so the charges
> generated by light build up the maximum base voltage to turn the
> transistor on. But every photo transistor I have seen in a mouse
> doesn't even have the base connection brought out to a pin. They are
> usually two pin devices, just collector and emitter, NPN devices.
>
> I would connect the emitter to ground and use a 10k pull up resistor
> to the positive supply. Then when you shine light on the transistor,
> it should pull down the resistor voltage to within about a half volt
> of zero. When kept in the dark, the resistor voltage should approach
> the positive supply voltage. Something like this:
>
> +5V
> |
> .-.
> | |
> | |
> '-'
> +--output
> |
> |/
> -|
> |>
> |
>
> 0V
> (created by AACircuit v1.28.4 beta 13/12/04 www.tech-chat.de)
>
> Once you get that to work, you can make an opto coupler out of that by
> sticking the infrared LED part of the mouse, lens to lens, against the
> photo transistor, with a drop of 5 minute epoxy.
>
> drive the LED through a 470 ohm resistor from the 5 volt supply, and
> you should be able to swing the photo transistor on and off via that
> light source. Then paint the whole thing black, to keep out stray light.


.

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