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IDX performance enhancement tip.
I have know about this for some time but thought I would share one of my recent experiments. I did this trick with the TGSL project but it turned out to be much more effective with the IDX project. It may have even been discussed in another thread.
A while back a few people discovered that subsituting an LF347 for the LM324 in U3 gave an instant improvement in sensitivity. This is generally because the offset of the LF347 is sometimes much less, and going through a handful of these can sometimes yield one or two really good ones. Typically, the LF347's I tested had a -2mV offset. The LM324's I tested were off by -10mv or more.
That means that the outputs have a long way to go to trigger pins 3 and 5 on U4!!!!.
Well why stop there? -2mV means quite a bit with targets on the outer reaches of depth..
Solution #1. Look for the perfect IC for U3 ( yes, you may have to go through a handful of LF 347's.)
Solution #2. Remove the ground wire from P5 and tie it to the negative 4v rail. (You can easily access
a trace on the PCB near U4). On the Silverdog boards it's easy to find this trace on top of the board. This allows you to pull
pins 2 and 4 of U4 slightly negative (about -1mV). Much closer to a -2mV offset.
Solution #3. Works good but not as well as solution #2. Remove the + 4v wire from P5 and tie it to the -4V rail.
If everything else is right, you can turn an IDX that detects rings at 8" into one that detects at 18"!!! (Air tests of course). With careful adjusting it still can run reasonably stable.
If your IDX cannot find a gold ring at 9" in the air, it will never find one that deep in the ground!
Don..
A while back a few people discovered that subsituting an LF347 for the LM324 in U3 gave an instant improvement in sensitivity. This is generally because the offset of the LF347 is sometimes much less, and going through a handful of these can sometimes yield one or two really good ones. Typically, the LF347's I tested had a -2mV offset. The LM324's I tested were off by -10mv or more.
That means that the outputs have a long way to go to trigger pins 3 and 5 on U4!!!!.
Well why stop there? -2mV means quite a bit with targets on the outer reaches of depth..
Solution #1. Look for the perfect IC for U3 ( yes, you may have to go through a handful of LF 347's.)
Solution #2. Remove the ground wire from P5 and tie it to the negative 4v rail. (You can easily access
a trace on the PCB near U4). On the Silverdog boards it's easy to find this trace on top of the board. This allows you to pull
pins 2 and 4 of U4 slightly negative (about -1mV). Much closer to a -2mV offset.
Solution #3. Works good but not as well as solution #2. Remove the + 4v wire from P5 and tie it to the -4V rail.
If everything else is right, you can turn an IDX that detects rings at 8" into one that detects at 18"!!! (Air tests of course). With careful adjusting it still can run reasonably stable.
If your IDX cannot find a gold ring at 9" in the air, it will never find one that deep in the ground!
Don..
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