madhippiescientist
New Member
I have built a LED DVM w/ the ICL7107 (using it's spec sheet
example), and it works pretty good, but...
When it's adjusted to match my multimeter's reading of an SLA
battery, it stays pretty accurate (+/- .02v). Then, if I hook it up
to a 9v battery, it displays up to a half of a volt lower than the
multimeter's reading. It seems that the LED DVM (ICL7107)
actually exponentially misreads voltage, with the farther away I
get from the original voltage adjustment (If I adjust it to the 9v
battery, then the SLA reads the voltage much lower than it is).
With even lower voltages (than 9), it's way off base. I am aware
that it's going to alter as it heats up, but I'm taking readings with
the LED DVM only being on for a very short while after it's prior
adjustment and a cooling down period. I have also tried it the
other way (leaving the meter on for a long time) but that just gets
the LED DVM to "endlessly" navigate away from it's adjustments
as time passes (and then the cold start shows it being far off). I
only need to sample every now and then, and it seems much more
stable when first "fired up", but I don't know why it is so far off
if taking a reading 4v lower than the one it was adjusted for. I
need to have it accurate throughout multiple ranges, and wonder
why it isn't or what it is I'm doing wrong. Or, is this chip simply
that inaccurate??
example), and it works pretty good, but...
When it's adjusted to match my multimeter's reading of an SLA
battery, it stays pretty accurate (+/- .02v). Then, if I hook it up
to a 9v battery, it displays up to a half of a volt lower than the
multimeter's reading. It seems that the LED DVM (ICL7107)
actually exponentially misreads voltage, with the farther away I
get from the original voltage adjustment (If I adjust it to the 9v
battery, then the SLA reads the voltage much lower than it is).
With even lower voltages (than 9), it's way off base. I am aware
that it's going to alter as it heats up, but I'm taking readings with
the LED DVM only being on for a very short while after it's prior
adjustment and a cooling down period. I have also tried it the
other way (leaving the meter on for a long time) but that just gets
the LED DVM to "endlessly" navigate away from it's adjustments
as time passes (and then the cold start shows it being far off). I
only need to sample every now and then, and it seems much more
stable when first "fired up", but I don't know why it is so far off
if taking a reading 4v lower than the one it was adjusted for. I
need to have it accurate throughout multiple ranges, and wonder
why it isn't or what it is I'm doing wrong. Or, is this chip simply
that inaccurate??
Last edited: