,

1)By sample time, means the time taken between each ADC sample, in my case this is 0.35 secs, which calibrates the filter to secs

2)By integration time, means adjusting your CR time whilst the processor is running, in otherwords the end user can adjust the filter time in mSecs,secs,minutes or hours to his desire.


Heres your difference equation:

y(n) = (1 - a) * y(n-1) + a * x(n-1)


How would I adjust it as outlined in 1 and 2 using your difference equation?



Correct, I introduced the negative sign to indicate the gradient dVc/dt goes negative during discharging and positive during charging.




Christoph, I am well aware of what Z transforms do, they produce iterative/recursive difference equations whilst Laplace/Heaveside_switchers transforms transform from the frequency domain to time domain. There are other much easier ways of handling differential equations, like using commutating methods, which I use, but we don't even have do that and infact we can run a differential equation(ODE) directly in software with a little thought.

we have....

dVc=[(E-Vc)/cr]*dt.....(1)charging
dVc=[(Vc-E)/cr]*dt.....(2)discharging

final output(Vc(t+1))=Vc(t)+dVc

cr= adjustable integration time of the filter
dt= sample time, in my case 0.35 secs

Heres my CR filter routine....

 In_filter:
Dti = Adc_present - Adc_last ;test charging/discharging
If Dti < 0 Then              ; if neg. then exec. following code
Dti = Adc_last - Adc_present
Dti = Dti * 0.35             ; calibrate filter to secs
Dti = Dti / Fil_time         ; fil_time=cr time (adjustable)
Adc_last = Adc_last - Dti    ; form final output
Gosub Disp                   ; display it
Return                       
End If
Dti = Dti * 0.35             ; if discharging then go here
Dti = Dti / Fil_time
Adc_last = Adc_last + Dti
Gosub Disp
Return

Cheers
Jason