LTC1298 + Loadcell = heating element?
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Posts: 46,084
Does anyone know of any good reading, dealing with any ADC
attached to the bs2sx, which will let me read a differential voltage
instead of two seperate channels?<p>
I don't know 1/4 of what you guys do, but I want to have
some fun too, and led's just don't cut it anymore.<p>
My loadcell is a Tedea 1040-41. 2mv/V out.<p>
I "roasted" a ltc1298, and know where I screwed up. Should I
keep trying them, or is there something better/cheaper that I should
try to get to work?<p>
Any help would be really appreciated!!<p>
Thanks,<br>
Dana
attached to the bs2sx, which will let me read a differential voltage
instead of two seperate channels?<p>
I don't know 1/4 of what you guys do, but I want to have
some fun too, and led's just don't cut it anymore.<p>
My loadcell is a Tedea 1040-41. 2mv/V out.<p>
I "roasted" a ltc1298, and know where I screwed up. Should I
keep trying them, or is there something better/cheaper that I should
try to get to work?<p>
Any help would be really appreciated!!<p>
Thanks,<br>
Dana
Comments
>My loadcell is a Tedea 1040-41. 2mv/V out.
>
>I "roasted" a ltc1298, and know where I screwed up. Should I
>keep trying them, or is there something better/cheaper that I should
>try to get to work?
The LTC1298 is one of the nicer parts in this application. Here's why: the
mux in the '1298 allows you to reverse the inputs while in differential mode.
The reason for this is to allow you to remove the offset error of the
differential amp that you use to amplify the signal from the strain gauge
(idea from a Motorola app note). We use 74hc4052 muxes between the load
cells and the diff amp. Each load cell uses 2 inputs on the mux: one way
connects the load cell straight to the diff amp, the other input does the
same thing but reversed. The output of the diff amp feeds the '1298 directly.
You read the strain gauge with the input mux one way, then reverse the
input mux and read it again. Add the 2 readings together to get a 13 bit
result. Note that any amplifier offset has now been cancelled out.
The diff amp is just a dual op-amp. Strain gauge feeds both (+) inputs,
gain set resistor between both (-) inputs, feedback resistors between each
amp's output and and its (-) pin. Note that you don't need the typical 3rd
op-amp of an instrumentation amp because the '1298 has differential
inputs. Both feedback resistors are equal value and gain is the sum of
both feedback resistors divided by the gain set resistor.
Note that in the projects that I've done using this technique, I set the
input mux one way, then read the '1298 both ways. Then reverse the input
mux and read the '1298 both ways again. 2 of the readings will be zero,
the other 2 readings are the ones that you want to use. Its been several
years since I last looked at that code but I *think* that all I did was add
all 4 readings together.
Bottom line: using the '1298 allowed me to use a much less expensive diff
amp and *really* reduced the overall project time and cost.
dwayne
--
Dwayne Reid <dwayner@p...>
Trinity Electronics Systems Ltd Edmonton, AB, CANADA
(780) 489-3199 voice (780) 487-6397 fax
Celebrating 19 years of Engineering Innovation (1984 - 2003)
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the transducer to the instrumentaion amp and then to A/D.
I think it is better to use devices designed specially for load cell like:
* AD7730: CMOS, 24-Bit Sigma-Delta, Bridge Transducer ADC for load cell
* CS55XX: 16/20-Bit Bridge Transducer A/D Converters.
>From: "dana_basic_stamp" <dana_basic_stamp@y...>
>Reply-To: basicstamps@yahoogroups.com
>To: basicstamps@yahoogroups.com
>Subject: [noparse][[/noparse]basicstamps] LTC1298 + Loadcell = heating element?
>Date: Tue, 25 Mar 2003 21:44:26 -0000
>
>Does anyone know of any good reading, dealing with any ADC
>attached to the bs2sx, which will let me read a differential voltage
>instead of two seperate channels?<p>
>
>I don't know 1/4 of what you guys do, but I want to have
>some fun too, and led's just don't cut it anymore.<p>
>
>My loadcell is a Tedea 1040-41. 2mv/V out.<p>
>
>I "roasted" a ltc1298, and know where I screwed up. Should I
>keep trying them, or is there something better/cheaper that I should
>try to get to work?<p>
>
>Any help would be really appreciated!!<p>
>
>Thanks,<br>
>Dana
>
>
>
>
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