PC-Driven EGO Sensor Analyser (Jan/Feb 1996):
 
VR1 is listed incorrectly in the parts list -- it should be 1k as shown in the
circuit diagram, while capacitor A2 on the overlay diagram is really C6, and 
its positive leg should go to battery positive.  Also we have found that some 
TL074 ICs were not able to sink enough current to drive the optocouplers fully.
 To rectify this, we have come up with a simple modification to fix this 
problem. Cut the track between the junction of resistors R31/R32 and pins 1 
and 2 of U1, and also replace R21 and R22 with two 1k resistors. Remove the 
'Power' LED, and install a pair of 1N4148 silicon diodes wired in series in 
its place, and reconnect the 'Power' LED with a 2.2k dropper resistor directly 
across the 'Bat+' and 'Bat-' terminals. Finally, connect the 'Sig. ground' 
terminal to the 'LED1 a' terminal with a short length of hookup wire. The 
diagram below shows the additions needed. - see ego_pic.exe.

A number of readers have pointed out that the front cover of the January issue 
shows an engine running with a lambda of 1.38 and that the AFR and oxygen 
percentage calculations were incorrect. Well, it seems that we can't fool our 
eagle eyed readers and we will now have to admit that the values shown were 
'hard wired' into the display, as the software had not been finalised in time 
for the photo. Rest assured that the finished version of the software 
calculates these values correctly, and that we won't try to dupe you again...