A person contacted me about the laser listener and asked if i knew an
equivelant IC to the SK3891, I knew an IC but one off the characters was wrong.
So you can use the Philips ECG829 or the SK3891. Sorry to all the folks that i
had given the wrong information.

An cyber friend of my build this circuit and this are his thoughts on the
project.

I tried all sorts of different phototransistors, and there wasn't much
difference between the different ones.

One might try using a 5k pot instead of R1 (the biasing resistor for Q1, to use
as a sort of sensitivity control - have to try that, though.

Interesting enough - there are quite a few (unlisted) alternatives to the
SK3891. These is the ECG829, which is said to be discontinued(?), the NTE829,
and the MC3340P, which is a Motorola chip, giving the same performance as the
NTE829 (I actually bought one of each and checked - no difference between the
two). All these chips are pretty inexpensive, around R12 in SA, which works out
to be _roughly_ 1 pound (UK), or 2 US Dollars. The Motorolla MC3340P was the
easiest to come by, though - I had to specially order and wait for the NTE829
or ECG829, but the MC3340P was in stock at every store I tried.

Further, if you don't feel like buying the (relatively expensive) optional
meter, the whole 741-part of the circuit may be left out - ie everything to the
right of and including R4 and C7, excluding J1, B1 and S1, all for obvious
reasons. Spelt out, you can leave out R4, C7, C9, R5, IC3, R7, C10, D2, D1,
C12, R8, C11 and M1.

Thanks Jan for the great info