Instrumentation Amplifiers
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Instrumentation Amplifiers If you have a ground offset problem with your
wideband, you can fix it pretty cheaply with an
external instrumentation amplifier. Here is some
info on one I built for my HPTuners EIO cable.
http://www.analog.com/static/importe...eets/AD620.pdf
is the AD620 IC instrumentation amplifier. I power
it with two 9V batteries so that it "floats" relative
to vehicle ground. Its output is referred to EIO
ground, and is the difference of WB out to WB
ground. Any ground offset is rejected. The AD620
needs no external components to get a gain=1
difference amp.
First pic is the little board w/ batteries. Input is
from WB output jack, output is pigtails to the EIO
green connector. Second pic is board detail. I add
1Kohm input and output limiting resistors (1Kohm)
just in case of faults, and a pair of 0.1uF decoupling
caps at the battery inputs.
Third pic is the output characteristics; there is a
0-30mV (out of 5V, so < 1/2%) error in the output
voltage across a ground-difference of -2 to +2V,
over the -0.5 to +5.5V input difference range.
The output traces (diagonal line) cannot be
distinguished from each other despite being up to
4V different in offset.
Parts - you will want
(1) AD620 amplifier
(2) 0.1uF, 20V caps
(4) 1Kohm resistors
(2) 9V battery clips
(1) 8-pin DIP socket
(1) small piece of perfboard
(1) handy box, maybe
(1) stereo 1/8" headphone cable or whatever fits
your particular wideband's 0-5V output.
All but the AD620 can be had from Radio Shack.
Total cost ought to be under $20.
wideband, you can fix it pretty cheaply with an
external instrumentation amplifier. Here is some
info on one I built for my HPTuners EIO cable.
http://www.analog.com/static/importe...eets/AD620.pdf
is the AD620 IC instrumentation amplifier. I power
it with two 9V batteries so that it "floats" relative
to vehicle ground. Its output is referred to EIO
ground, and is the difference of WB out to WB
ground. Any ground offset is rejected. The AD620
needs no external components to get a gain=1
difference amp.
First pic is the little board w/ batteries. Input is
from WB output jack, output is pigtails to the EIO
green connector. Second pic is board detail. I add
1Kohm input and output limiting resistors (1Kohm)
just in case of faults, and a pair of 0.1uF decoupling
caps at the battery inputs.
Third pic is the output characteristics; there is a
0-30mV (out of 5V, so < 1/2%) error in the output
voltage across a ground-difference of -2 to +2V,
over the -0.5 to +5.5V input difference range.
The output traces (diagonal line) cannot be
distinguished from each other despite being up to
4V different in offset.
Parts - you will want
(1) AD620 amplifier
(2) 0.1uF, 20V caps
(4) 1Kohm resistors
(2) 9V battery clips
(1) 8-pin DIP socket
(1) small piece of perfboard
(1) handy box, maybe
(1) stereo 1/8" headphone cable or whatever fits
your particular wideband's 0-5V output.
All but the AD620 can be had from Radio Shack.
Total cost ought to be under $20.
ad620, amp, amplifier, amplifiers, amps, board, differencing, hptuners, ic, instrumentation, list, radio, radioshack, shack, tuning
