Hi,

I'm currently trying to implement the ADC from the MSP430F168 chip.

Anyhow, i just have a question in regards to making the ADC value 
stable.

THe problem i'm having right now is that i have a stepper motor and 
a load cell.  I'm basically reading the values coming from the load 
cell by using the ADC and controlling the stepper motor via MSP430.

Anyhow, when i run the stepper motor i notice that some of my adc 
values are spiking, it seems like there is a lot of noise.  But this 
does not occur when the motor isn't moving.  Can this be the cause 
of EMF coming from the motor?  

Anyone have any suggestions on how to improve the signal?  I used a 
lowpass RC filter prior to entering the ADC.

Is it possible to synchronise your ADC readings until after the motor 
has stepped and stabilised? If not you might want to try a simple spike 
filter:-

Take 6 readings, deduct the highest and lowest, then average the 
remaining 4. You can usethis as a decimation filter (6 readings become 
1, so sample rate must be higher) or as a moving window. You might also 
try reducing the sample period. Synchronisation will work the best I 
believe. A simple average or IIR filter won't work well, since the spike 
spreads through many subsequent readings. An FIRlow pass filter will, 
provided you then backtrack the output to remove the slight hump that 
will still be there. (The spike still has low frequency components.)

Al

tom_sun79 wrote:

> 
> Hi,
> 
> I'm currently trying to implement the ADC from the MSP430F168 chip.
> 
> Anyhow, i just have a question in regards to making the ADC value 
> stable.
> 
> THe problem i'm having right now is that i have a stepper motor and 
> a load cell.  I'm basically reading the values coming from the load 
> cell by using the ADC and controlling the stepper motor via MSP430.
> 
> Anyhow, when i run the stepper motor i notice that some of my adc 
> values are spiking, it seems like there is a lot of noise.  But this 
> does not occur when the motor isn't moving.  Can this be the cause 
> of EMF coming from the motor?  
> 
> Anyone have any suggestions on how to improve the signal?  I used a 
> lowpass RC filter prior to entering the ADC.
> 
> 
> 
> 
> 
> 
> 
> 
> .
> 
>  
> Yahoo! Groups Links
> 
> 
> 
>  
> 
> 
> 
>