cheap probe to detect log growth

[Michael Witty]

Dear All, I am convinced there must be a better way of finding the log
phase of growth (for example of a conical flask of E. coli) than
repeatedly taking 1ml samples and putting them in a spec.

     My ambition is to have a cheap detector with a probe consisting of a
light source and photoresistor which can be dangled into my flask and
record data continuously.

     But I am a biologist not an electrical engineer.  Does anyone share
my ambition?  Or know how I can make this happen?  Mike.