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1  Using Arduino / Sensors / Re: ADS1232 24-Bit ADC to Arduino UNO Trouble on: November 05, 2012, 04:24:54 pm

Spot on my friend!  Perfect example.  I modified the details to fit my setup and it works great.  Thanks a lot!  Interesting part is the SPI library isn't even used, but it outputs great numbers!
2  Using Arduino / Sensors / Re: ADS1232 24-Bit ADC to Arduino UNO Trouble on: November 01, 2012, 05:33:11 pm
To add, important wire connections between the Arduino and ADS1232 are as follows:

ADS DRDY/DOUT <----> Arduino Pin 12 (MISO)
ADS SCLK <-------------> Arduino Pin 13 (SCK)
ADS PDWN <------------> Arduino Pin 10 (SS)

These are the only 3 connections for SPI I can see on the ADS1232.
3  Using Arduino / Sensors / ADS1232 24-Bit ADC to Arduino UNO Trouble on: November 01, 2012, 05:28:25 pm
I'm ultimately trying to read the ADS1232 with the Arduino for a scale project.  The ADS1232 is a great chip to use for this application as it is basically designed for scales and other sensitive bridge applications that require a lot of increments for a good resolution in output.

I am a beginner in using SPI, so I am trying to follow an example to start.  This one here seems to be the closest out there: http://dangerousprototypes.com/forum/viewtopic.php?f=2&t=4247&p=42053#p42051 however, the output doesn't seem to make sense.  I can tell there is some conditioning for the specific application, but when I apply low amounts of weight, the output will slightly decrease, then jump to increasing values and increase respectively to the amount of weight applied.  I have iterated with adjusting various lines in the code to see if I can get a more linear result, but have yet to be successful.

The data sheet for the ADS1232 http://www.ti.com/lit/ds/sbas350f/sbas350f.pdf definitely divulges the requirements for proper operation such as clocking and so on, even a specific scale application example, but modeling my circuit after this and using the example code, I just can't seem to output a linear decimal result.  I have a feeling the ADS isn't being clocked right, but I really don't understand or know how to ensure this.  Page 19 in the datasheet discusses Data Retrieval.

Anyone have experience here that can help?  I'm literally only trying to output a decimal answer from the ADS1232 to convert into a weight...

Thanks in advance!
4  Using Arduino / Sensors / Re: Strain Gauge to INA125 Troubles on: October 16, 2012, 05:54:35 pm
So the no load voltage should be zero, and to accomplish that, I would need to modify the circuit to trim it to zero?  I tried googling around but mostly found circuits to balance the bridge.  Is that the same?  I was assuming the bridge was factory balanced as there is no additional components on the original circuitry from the scale.  The leads go strait into the microcontroller under the edge of the sealed black blob.

Any verified examples I could compare my situation to to attempt to zero out my bridge?  BTW, the bridge appears to be made of the apposing strain gauges (3 wire each) crossed into the 4 outputs of excitation and sense, both +/-.

Thanks again for helping me with this..
5  Using Arduino / Sensors / Re: Strain Gauge to INA125 Troubles on: October 11, 2012, 04:38:23 pm
Some good and bad news. I flipped the + for the - on the bridge inputs and this seemed to help in allowing the voltage to go beyond the point it did before.  I noticed that when I place the excitation voltage on the 5V instead of pin 4 as suggested by the datasheet, the sweep is larger.  So, the good is the overall sweep is pretty well dialed in as far as allowing 2kg of force, but (the bad) there seems to be no way to allow a sensitive reading.  The scale is capable of sensing 1/2 a gram but I can't seem to get it to change voltage from the no load point until about 50g or so of weight.  Could this be an indication of a bad amp selection?  Other possibilities?
6  Using Arduino / Sensors / Re: Strain Gauge to INA125 Troubles on: October 10, 2012, 01:45:23 pm
Well, the scale originally only used 3V, so I figured why bump it to 5V if it isn't necessary?  I put it to 5V just to see if it improved.

I knocked the Rg up to 88 ohms and it seemed to lower the no load voltage from 3.02V to 0.88V.  I noticed the circuit is much more sensitive to interference as well.  If i put my hand near the scale or IC it will change the Vo by lowering it (seems to be the case for both 22ohm and 88 ohm, but stronger at 88 ohm).

After the changes, there seems to be no improvement with the range.  The Vo still drops to 0.07V (lowest it goes) at around 500g weight applied.

I wired up the INA125P just as the datasheet shows in the pic attached.  I used the 2.5V ref pin 14 into 4 as shown.

Even with a simple INA128 I had the same results as this.  Is it the load cell?  It has the E+ E- S+ and S- outputs like any other.
7  Using Arduino / Sensors / Strain Gauge to INA125 Troubles on: October 09, 2012, 05:54:28 pm
So I purchased a 2kg scale with the intention to link it to an arduino to send the scale readings to the serial port for further use.  I obtained a INA125P In-amp with the hopes to amplify the signal to do this.  There are several examples out there of folks hacking scales in this manner.  I am running into some issues where the output sweep seems to be limited and I'm not sure why.

The resistance on the bridge is 1k ohm (reading between V- and V+).  The excitation V is 3.3V.  The voltage to the INA125P is 3.3V.  The reference is the INA125P on-board 2.5V.  I have had trouble finding a solid gain to amplify the signal, and it seems a resistor of 22 ohm gives a reasonable sensitivity of the scale response to minimal weight but the amp seems to saturate at about 500g.  When weight is applied the voltage drops from the max voltage to zero at about 500g and anything beyond that just sits at a little above zero.  I was hoping to replicate the scale at the full 2kg.  Why would the amp be saturating at only 500g?  I've tried other gains with pots and resistors, but nothing really outputs a reasonable sweep beyond 500g, or requires too much force to sense readings from the sensors.

Greatly appreciate any insight & help.  I am by no means an EE and am trying to learn! smiley

This is essentially the circuit minus the shown RL resistor (from the data sheet).

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