Analog with FPGAs

[Wond3rboy]

Hi, i have started out with FPGAs recently. Have started working with a Spartan 3E kit. I have already covered the basics and some small projects. I am using VHDL for programming. I intend to make a Hybrid Energy System(Solar+Wind Turbine) for which i am going to tackle the easy part first(solar) and than move on to the wind turbine thing (cause i will need to employ pitch and yaw control). Since i am not very experienced in FPGAs, i wanted some hints on what would be the easiest/cheapest way to go about doing it. Thanks.

 

[kubeek]

I think you first need to decide what you need to control and how you want it to be controlled. Then we can discuss what to do with the fpga

 

[RichTheDude]

FPGA’s and power efficient applications are not something that go together usually, FPGA’s can be very current hungry with large designs.

Anyway analogue processing in an FPGA is usually done with the following system. ADC (Analogue to Digital Converter) -> FPGA -> DAC (Digital to Analogue Converter). ADC converts the continuous analogue waveform into a discrete time n bit number where range of the number is 0 to 2^n. This a fractional number where it represents voltage as of ADCnumber * ( Vreference/2^n). Where Vreference is a full scale reference voltage you will supply to the ADC.

You can then do control loops, filters or anything you wish to do mathematically with this number (for example a basic digital filter is basically a dot product Ʃax ) and then output this binary number to a DAC where it will be reconstructed into an analogue signal.

Only other I would like to recommend is you make yourself aware of aliasing, basically you will get nonsense results from your ADC if your input signal has a frequency > ½ of your ADC sampling frequency.

 

[Wond3rboy]

Hi, thanks for your replies.

@kubeek: The idea is to accomplish energy management(regulate the amount of power being delivered by the two sources) using the FPGAs as well as the solar tracker for the Solar Panel and a Wind turbine controller for the wind turbine. I intend to do it with an FPGA.

@RichTheDude: Thanks for the tip. I have good experience in working with PICs and have used its ADC module. What i wanted to know was whether i required some board to do analog signals with FPGAs or not. I will go for an IC.

I know a microcontroller would perhaps be a better option for this, but it is a study kind of project that i am undertaking. Thanks again.

 

[RichTheDude]

Ah . If you could move to another platform the Actel SmartFusion (http://www.actel.com/FPGA/SmartFusion/index.html#tab3 ) has ADC,DAC and other analogue building blocks built into the FPGA albeit at low sampling rates.

Never used one, and I have been told the number of write cycles on the flash is very low – so be careful if you do consider it.

 

[Wond3rboy]

Thanks RichTheDude. It could definitely be a nice tool(save up a lot of time ) and at 99$, i bet i can get hold of the evaluation kit. The sampling rate is not an issue since i will not be working with fast changing quantiities.