controlling band-pass filters

[aidanbre]

i am using a pic16f877 and want it to control the action of six band-pass filters in order to enhance a radio signal.this is done by switching between filters. is there a standard source code i could use or could somebody point me in the right direction?

 

[Chippie]

Errmmm.......lemme see.


Well,the pic is able to switch the caps in and out but how do you know when the pic has to do this ?

Can you expand a little more please ?


regards Chip

 

[kinjalgp]

Search for "Switched Capacitor Filter" in google. ICs are available from several manufacturers for this.

 

[Pilot]

i am using a pic16f877 and want it to control the action of six band-pass filters in order to enhance a radio signal.this is done by switching between filters. is there a standard source code i could use or could somebody point me in the right direction?

Are the band pass filters a commercial unit on one board. If so do they use pin diode inputs for switching or is it variable voltage?

Is it a homebrew or commercial rx/tcvr you will be using?

If commercial then most of the modern ones use voltage levels for bandswitching. If an older type then mechanical switches.

If it is pin diode switching on the bpf board then all you have to do is select a different output per band from the PIC and send high/low as required.

If the rx/tcvr is mechanical switches then just build a simple buffer/interface and take individual band selections to different inputs on the PIC.

From that point some whiz with a PIC - I don't use them, not got a clue - on this forum can come up with a simple enough program for you.

It may be worth adding a bpf selection indicator to it - make sure you got the right one selected.

 

[Take_UR_PIC]

Build your filters using serially controlled DIGIPOTS like the MCP41XXX/42XXX family from Microchip, then use the serial interface of the PIC to program the filters.

Use a LUT to characterise the filters then you can simplify the operation to setting up a frequency and usign this to reference a value in the LUT which is then programmed into the POTs.

To get better resolution then the 256 steps provided, you could series or parallel multiple pots to get the values/resolution you want.

Try here, http://www.xicor.com/pdf_files/an53.pdf an application note that details how to use these devices.

I have a PDF document I can try to upload here.

let me have your email and I'll send you the APP note I have. it will help you a LOT![/url]