Whats the purpose of this transistor?

[Hybrid fourdoor]

In this article it contains the following schematic, I understand what most everything is doing except that transistor in the middle.

 

[JOE DIRT®]

with not even looking at the article or looking at the circuit that close...LOL....shoot me!!!...its a basic switch for the comparator.....so disregard what I just posted

DIRT®

 

[bpetrus]

It adds an offset ("85 mV Deadband") between the 2 comparators (pins 5 and 6) since the voltage at pin6 is given by

Vpin6 = Vpin5 + Vbe * (10k / 62k), with Vbe = 0.6

 

[bpetrus]

Oops, the offset should be:

Vpin6 = Vpin5 + Vbe * 10k / (10k + 62k), with Vbe = 0.6

brad

 

[Hybrid fourdoor]

Also for this circuit instead of the Crystal digipots, could I use Maxim DS1802's which have the pushbutton control? I happen to have two 1802's allready so that would be easier to use.