Subject: [OT] Need help with phototransistor

Rafael Pinto wrote:

<SNIP>
>  I am using a TIL78 activated by a LED (yellow). Can anyone suggest
>  other cirucuit?

This is just my guess, but most phototransistors are more sensitive to
red and IR light.  Perhaps your yellow LED isn't being seen by the PT.

Either switch to red, or if you can't for some reason, then a photodiode
might be a better choice as they usually are sensitive to shorter
wavelengths.  I have seen an advertisement for photodiodes down to 214nM.

Remember though, that in general a photodiode will produce less
photocurrent than a phototransistor (roughly the same detectivity,
though).  If the light from the LED is weak, then you might have to hook
up to additional circuitry to detect the LED.

Just my thoughts.  Your mileage may vary.

Michael

REMOVE THE .NS (NO SPAM) FROM MY ADDRESS TO REPLY
*****************************************
The strong do what they have to do and
the weak accept what they have to accept.
                             --Thucydides