[minima] Re: Linear Output Filter Switching

  • From: Frank <w4nhj@xxxxxxxxxxx>
  • To: minima@xxxxxxxxxxxxx
  • Date: Sat, 01 Feb 2014 06:50:02 -0500

Farhan and all,

It seems like the Arduino Uno chip is just about maxed out. The mega2560 chip has much more capacity, but it is very expensive, approximately $15 US and is SMD which would make it hard to solder. Perhaps a second Arduino Uno chip to give many more features in the future. Perhaps another Si570 for a variable BFO, CW keyer, etc.. Of course these would be options enabling one to build the basic Minima cheaply and add as money allows.

Frank - W4NHJ

On 2/1/14, 12:00 AM, Ashhar Farhan wrote:

I have been mulling over this ... and I am trying to balance quite a few things here.

1. Can we make do with just four filters? I have attached a screenshot of a simulation I ran (both these programs are available on the EMRFD CD). As you can see, a filter can be cut for 7 and 10 mhz. The 7 mhz's second harmonic at 14 is down by 25db. Which means, if we don't distort the linear too much, we can get more 43 db suppression of the harmonics. If you guys agree to this , then, I propose as follows :
 1st filter for 3.5 MHz
 2nd filter for 7-10 mhz
 3rd filter for 14-18 mhz
 4th for 21-28 mhz
These will have to be three section filters, which is alright. A 1-of-4 decoder like 74LS139 could do the switching with just 2 lines.

2. The switching of the main filters is at variance with this scheme. so, we will have to use a dedicated line (as we are doing now) to switch these filters.

3. There is a third line A0 (pin 23) that is unused. this can be used to switch in a higher bandwidth filter (more than 10 Khz). with this filter, the broadband audio can be fed to an 'SDR' back-end like linrad. The serial port can provide the tuning control.

- f

On Sat, Feb 1, 2014 at 7:01 AM, Dan Reynolds <on30ng@xxxxxxxxx <mailto:on30ng@xxxxxxxxx>> wrote:

    I'm not any kind of an expert but could you use a Microchip
    MCP23017 I/O expander on the 5 V side of the I2C bus. I was
    thinking something like I saw on the Tronixstuff page here:
    Instead of a LED an I/O line could drive a transistor to drive a
    Then the code could "watch" the frequency and as it changes the
    output line for that particular LPF could be switched.

    Or could you use a 74HC595 to accomplish the same thing.

    I was going to approximate the Minima front panel with a bare
    bones Arduino and some parts and see what I could dream up.
    I don't really know what I'm doing. I'm just muddling through
    trying to patch bits and pieces together...

    Dan -- KB9JLO

    On Fri, Jan 31, 2014 at 6:10 PM, Wayne McFee <nb6m@xxxxxxx
    <mailto:nb6m@xxxxxxx>> wrote:

        Hi Mark,

        If the three outputs were set up as you suggest, a Picaxe chip
        could be programmed to control either individual relay driver
        transistors or a relay driver chip like the 2903(?).

        I've been using that arrangement for filter selection  in a
        homebrew rig.

        Or, if one of those output lines could be programmed to output
        a stepped voltage such as that provided by the FT817 for
        bandswitching info, that makes the programming even easier.

        Wayne NB6M

        > On Jan 31, 2014, at 1:24 PM, Mark G0MGX
        <mark.g0mgx@xxxxxxxxx <mailto:mark.g0mgx@xxxxxxxxx>> wrote:
        > Farhan & Team,
        > I can see that we have provision in the schematic for 3
        digital outputs for band selection, but can only see one of
        these (BAND_HI - pin 11 - Arduino D5) being used within the
        function "setBandswitch". It is this function that currently
        selects the LPF used based on frequency.
        > We could set the state of the three outputs based on
        frequency something like this:
        > <Filter Ideas.png>
        > But someone far cleverer than I would need to explain how to
        create relay on/off switching based on the logic states of
         the three lines - I have no idea how to do that!
        > If we were to implement something like this was the
        intention to use these additionally switched filters in RX as
        well as TX?
        > I would be interested in your thoughts and ideas on how you
        saw this working before I head down the wrong road with my
        > Many thanks,
        > Mark
        > G0MGX

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