"To all the downvoters of my comment above, do you really need to be told that a transistor is a digital switch? on an El Reg Forum?
I didn't downvote you (I don't use the up/down vote thingies, because I am over 12 years old) but my memory of college fiddling with transistors and doing calculations about how to bias the base so that it operated in the "knee" part of the accompanying datasheet graph made them work in a very analogue way as they were transitioning. Hence the analogue output of a transistor amplifier. They can work as a switch, but there is more to a transistor than the behaviour of a relay.
Of course, this makes no difference the way that transistors are being used for this project.
After I left college and fell into the world of hardware development, I found that using transistors in projects was done using shortcuts and I didn't have to think about all that NPN PNP shit ever again.
Off the top of my head, did silicon bias at 0.7V, germanium at 0.5V? It''s been 25 years since I did hardware, little has been retained.