[PIC] problem with ADS1230 interfaced ti PIC

[tamilarasantpvm]

hai frnds,
i am new to ADS1230 ADC converter. i am interfacing the ADS1230 with PIC controller. i developed the code and the Hardware also. when i tried to test the code on the hardware i got to find that the DRDY/DOUT pin in ADS1230 is in HIGH and it does not provides the ready signal to the controller. I tried to find the problem a lot. but i coundnt. i found this fault through the scope.
can anyone help me in this regard. hope u help me.
thanks in advance.

With Regards
Tamilarasan V

 

[udayan92]

Could you put up the code please?

 

[tamilarasantpvm]

hi udayan92,
thanks for the reply. can u clear me one doubt. I connection the following connection

DVDD, REFP, AVDD shorted and given to 5v
DGND, REFN, AGND shorted and given to GND
AINP and AINN to output of loadcell
SPEED, CLCK, GAIN shorted to ground
PWDN to high after 1S of VDD on
Connected 104 across CAP pins

these connection are given and i am monitoring the DRDY/DOUT pin in the scope.
will the DRDY/DOUT becomes low after conversion.

for me the DRDY/DOUT pin does not goes low. it remains in high state itself.

 

[FvM]

these connection are given and i am monitoring the DRDY/DOUT pin in the scope.
will the DRDY/DOUT becomes low after conversion.

Is SCLK low in idle state?

 

[ud23]

PWDN to high after 1S of VDD on

See the power up sequence in attached image and see the fig 31.
what is the supply to your load cell?

 

[tamilarasantpvm]

problem with ADS1230 interfaced PIC

Thanks for all ur help frnds. it is working now. i got the data ready signal and i read the adc value. now i face the conversion problem. how to convert the 20 bit data received into weight. my load cell voltage is 5v, max load measured is 3kg. suggest me with some example codes. i am interfacind ADS1230 with PIC. so if u have pic examples give me..

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[paulfjujo]

Show your schematic..
Datasheet of the load cell ?

you load cell must only deliver any mV
industrial standard for load cell is 5mV/full scale of measure /excitation Volt
so maybe near 25mV at 3Kg
give us the relation chip between raw measure ( ADC 20 bits value) you get with for 0 Kg
and value for 2 Kg (75% full scale) or 3Kg (100% full scale)
if your measures seems correct , you can go further..

What PIC
What compiler ?
How do check the raw meaure ( LCD, RS232 terminal via UART... ) ?

 

[tamilarasantpvm]

hi paulfjijo,
thank u for your reply. i am providing the details u asked below.

i attached the loadcell datasheet. i have CZL601, 3Kg loadcell. but i didnt get the datasheet for 3kg load cell. i got this datasheet only.
i am giving the excitation voltage as 5V. but the datasheet shows as 9 - 12v. is it right to give 5V. i am using ADS1230 to convert the analog value. this IC supports only 5v. i cant use greater than that. what can i do. suggest me. compiler is Hi-Tech.

I am getting 10.9mv as no load differential voltage. but the rated output is 2mv/V. but how can i get 10.9mv as no load diff voltage.

i am displaying the raw value in the 7segment display through MAX7219 display driver. i am using PIC16F886 controller.

 

[FvM]

The load cell should work well with 5V excitation.

Offset is about full scale signal which shouldn't happen. Of course we can't see the reason from a distance. Is it a used loadcell that already might have experienced overload?

Did you check the output offset without connected measurement circuit, only excitation by a lab supply? You can also check if it's a constant relative offset (expectable).

In any case you'll zero the offset in software, so there should be no problem to use the loadcell anyway.

 

[tamilarasantpvm]

Hi FvM,
yes, u r right. it is a used loadcell. it might have been applied with overload.
i too have the same idea of making the initial offset zero.. but in this case how can i convert the adc counts into the voltage level. can u help me by giving me a excel file explaining the relation between adc count, load cell output, voltage level after gain from amplifier, weight on the scale.

my gain is 64.

 

[tamilarasantpvm]

sorry.. i couldnt get you. what do u mean by scale_adccount and scale_weight

 

[FvM]

You'll assume linearity and perform an over-all calibration for zero and (full or partial) scale.

You get zero_adcount and scal_adccount.

actual weight = (actual_adccount - zero_adccount)/(scale_adccount-zero_adccount)*scale_weight.

- - - Updated - - -

It's the weight and achieved ADC count of a calibration weight.

 

[paulfjujo]

hello,

Something is wrong ...

Are you sure about the loadcell wiring connection ?
if you turn the loadcell bridge of 90° ! you get an unbalanced output wich can explain this 10mV output
if Excitation applied btween CD and signal pick up on AB !



full scale signal is ~10mV , same level as zero offset ?
Is the loadcell without mechanical added part ?
Can you check your loadcell with 3kg applied on it , what is the output value in this case ?

 

[tamilarasantpvm]

hi,

i am working on all ur suggestion. let me reply about it later. now i need a help on speed of the ADC convertion.

if i test the ADS1230 alone with a scope. i am getting the data ready pulse at 100ms exactly. but when i connect it with the controller i dont get the dataready signal in 100ms interval. it take time interval of 770ms. what maybe the reason. i am using 2uS for each clock pulse. i am doing it using interrupt. so the timing cannot be missed. but this is the timing sequence i observed from scope.

also please tell me how to convert the raw data from ADS1230 i.e., 2's complement data into ordinary decimal value. only the signed bit must be scaned for conversion or the whole data to be involved in some conversion formula..? kindly help me in this regard.

- - - Updated - - -

hi frnd,
i have an additional clarification. what will be the ADC count read from ADS1230 after running the calibration cycle to the ADS1230.

i run the calibration cycle by providing 26 clk pulse after the data ready signal from the converter. when i receive the next ready signal i am reading the adc count from ad1230. by this time i am getting the same count as before the calibration cycle. is it right. or i have to do some changes.

 

[FvM]

ADS1230 data output format is two's complement. For full resolution, you would convert it to a long (signed 32 bit) data type by sign extension. Or reduce the resolution to int (signed 16 bit) by cutting the 4 lowest bits. If the internal calculations are performed in integer or float arithmetic depends on your application.

Conversion to decimal is a matter of the display routine, using formatted printf() or sprintf().

You'll get slow ADC operation if you either supply a slow external clock to CLKIN pin, or perform an offset calibration with every conversion (not suggested, I think).