[minima] Re: Linear Output Filter Switching

  • From: Mark G0MGX <mark.g0mgx@xxxxxxxxx>
  • To: minima@xxxxxxxxxxxxx
  • Date: Thu, 06 Feb 2014 11:52:06 +0000

Hi Team

I've done a bit more work on the output filter switching using a 4028 (which arrived today!).

The wiki is updated:


Including a link to a simple sketch to try and illustrate how it works and enable others to prototype the ideas as I have.

There will be more on this topic from me....


On 04/02/2014 19:05, Dan Reynolds wrote:
Thanks Mark. I'm learning a lot but you know how it is when you're dreaming - you never learn fast enough. I'm pouring over tutorials on the web to help me understand better.

I think I know what the schematic will look like but I just want to see it from a more credible source than my brain!

I hope to have the Boarduino and the front panel all mocked up by the weekend. I have an Si570 on the way. I'm going to use the WB6DHW Si570 board for the level shifter circuit.
That should also keep me out of trouble with modifying that one library...

Then I can start mocking up / playing with the LPF selection logic perhaps...

Thanks everybody. This is a neat project and I'm going to learn a whole lot!

Dan -- KB9JLO

On Tue, Feb 4, 2014 at 12:53 AM, Mark G0MGX <mark.g0mgx@xxxxxxxxx <mailto:mark.g0mgx@xxxxxxxxx>> wrote:

    Hi Dan & Team

    When I get the CMOS chips I have ordered I will publish to the
    Wiki the schematic for filter switching, details for interfacing
    to the bare bones Arduino and also publish my suggested code
    modifications/changes to control the switching based on radio
    frequency. I will also put extensive comments into the code to
    explain what's going on.

    The ULN2803a does look like a great option - I have just ordered
    some of those from eBay - so I will experiment with this option
    also in due course.


    On 03/02/2014 22:18, Dan Reynolds wrote:
    I wish someone could draw up a schematic and show a modified
    codes segment so someone dense like me can get his head around it.

    I looked at that CD4028 example and Mark, your second chart is
    starting to make sense...
    I think the ULN2803a is a good idea too.
    Do you ground the unused inputs on that chip?
    And then I assume the common on the output side would go to +12V
    for relay energizing power.

    This project could be an excellent learning project for me all
    the way around! :-)

    Dan -- KB9JLO

    On Sun, Feb 2, 2014 at 12:51 PM, Wayne McFee <nb6m@xxxxxxx
    <mailto:nb6m@xxxxxxx>> wrote:


        I'm using a ULN2803a Darlington Driver chip to drive the
        relays for LPF selection in a homebrew amp.  These have the
        back current diodes in them, so no external diodes needed
        across the relays.

        Just a thought, as it saves building individual drivers with
        transistors (like I did in another project).

        Wayne NB6M

        On Feb 2, 2014, at 6:54 AM, Mark G0MGX <mark.g0mgx@xxxxxxxxx
        <mailto:mark.g0mgx@xxxxxxxxx>> wrote:

        Hi Gang

        I've completed a proof of concept of the output filters
        today; it uses a 74141 as a BCD to individual selection
        connected to a 74LS00 used as NOT gates or inverters for the
        output lines.

        I can control this OK from the Arduino code, so I have
        ordered some of these CMOS 4028s as this has a HIGH output
        state when an output is selected whereas the 74141 is a LOW
        state when an output is selected (I have used 74141
        previously to ground cathodes of Nixie tubes!). This is the
        logic of the chip:

        <74141 logic.png>

        So I now wait for the postman before I can complete the
        filter output stage.

        I am thinking that we might like options in the code/filters
        as it seems to me we need to keep the current RX filter
        selection pin usage, but also use this for filter selection.
        We can go with very simple as suggested by Farhan and have 4
        filters, or we can have 5 to include either top band or 60M

        I will post more when I have the final design and code mods
        once built and tested. I am definitely going with a 3 line
        BCD output from the Arduino processor to select filters
        based on radio tuned frequency. This will be accomplished in
        the existing function "setBandswitch". Maybe (only maybe)
        something like this:

        <Filter Ideas3.png>

        In the code we will declare three digital outputs (including
        the existing BAND_HI) and set all three each time we change
        frequency, the state (HIGH or LOW) of each output will be
        dependent on frequency and in accordance with the truth
        table and output usage above.


        On 01/02/2014 18:47, Mark G0MGX wrote:
        very good. That CMOS chip used in the link looks the same
        as the TTL 74141 - but I am no expert.

        This does seem to be the way to go

        On 01/02/2014 18:24, mpcharlton@xxxxxxxxxxx
        <mailto:mpcharlton@xxxxxxxxxxx> wrote:
        Have a look at this halfway down the page...
        G6ZQS G-QRP 2247
        /-------Original Message-------/
        /*From:*/ Mark G0MGX <mailto:mark.g0mgx@xxxxxxxxx>
        /*Date:*/ 01/02/2014 17:29:09
        /*To:*/ minima@xxxxxxxxxxxxx <mailto:minima@xxxxxxxxxxxxx>
        /*Subject:*/ [minima] Re: Linear Output Filter Switching
        Isn't this:
        exactly what we need to go from Binary outputs on our 3
        digital lines to
        individual relays controlling filters?
        On 01/02/2014 15:26, farhanbox@xxxxxxxxx
        <mailto:farhanbox@xxxxxxxxx> wrote:
        > Mark,
        > There's something not right about the curve. The
        stopband is quite nominal. You must get atleast 60 db
        > Sent from BlackBerry® on Airtel
        > -----Original Message-----
        > From: Mark G0MGX <mark.g0mgx@xxxxxxxxx
        > Sender: minima-bounce@xxxxxxxxxxxxx
        > Date: Sat, 01 Feb 2014 13:47:38
        > To: minima@xxxxxxxxxxxxx
        > Reply-To: minima@xxxxxxxxxxxxx <mailto:minima@xxxxxxxxxxxxx>
        > Subject: [minima] Re: Linear Output Filter Switching
        > Hi Team
        > I've started the output filter Wiki page here:
        > http://www.hfsignals.org/index.php/Final_Output_Filters
        > and have so far put info on 4, 11 and 19MHz cut off Low
        Pass Filters. I
        > am very unhappy with the 19M filter sweep, so will let
        you guys take a
        > look before doing any more. The next filter needs to be
        30M cut off - we
        > already have one of those!
        > As an aside I have dug out my CD from EMRFD and mine is
        a 2002 version
        > of the software which I can't find a filter designer? I
        can enter values
        > myself but cant get the software to come up with the
        filter for me -
        > hence I have stuck with what I know and used QUCS for my
        > I do think that we could still use the existing D5 line
        for output _*as
        > well as*_ the existing input filter switching just so
        long as the line
        > stays HIGH for > 15MHz and LOW for <= 15MHz. This would
        give us room for
        > a 1.8M filter and another if we find we need i. I  have
        only focused on
        > those highlighted yellow below, but clearly with the
        three digital lines
        > we could have up to 8 filters if we needed them.
        > I personally like the idea of simple logic chip or BCD
        type logic to
        > control relays as I feel that we want to avoid more
        programming and
        > complexity where it's not needed. The 74LS139 idea is a
        great one and
        > probably the way I plan to go, but lets see what we decide.
        > I've tried to explain some of this in the Wiki - please
        take a look and
        > lets decide between us how we are going to do this part
        of the project.
        > We could of course go with the idea of a separate
        amplifier completely,
        > maybe with the tubes others are suggesting! I've never
        built anything
        > with tubes....
        > Mark
        > G0MGX
        > On 01/02/2014 06:48, Mark wrote:
        >> Thanks to everyone for the suggestions and ideas.
        >> If we go with 4 filters have we scrapped top band?
        >> I'll try and run some designs for the four suggested
        filters and build
        >> some prototypes and stick the results on the wiki.
        >> We can then decide and discuss what we think we should do.
        >> M
        >> From: Ashhar Farhan <mailto:farhanbox@xxxxxxxxx>
        >> Sent: 01/02/2014 05:00
        >> To: minima@xxxxxxxxxxxxx <mailto:minima@xxxxxxxxxxxxx>
        >> Subject: [minima] Re: Linear Output Filter Switching
        >> Mark,
        >> 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>
        >> <mailto:on30ng@xxxxxxxxx>> wrote:
        >>      I'm not any kind of an expert but could you use a
        >>      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
        >>      relay(?).
        >>      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
        >>      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...
        >>      73
        >>      Dan -- KB9JLO
        >> https://sites.google.com/site/on30ng/
        >>      On Fri, Jan 31, 2014 at 6:10 PM, Wayne McFee
        <nb6m@xxxxxxx <mailto: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
        >>          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
        >>          construction!
        >>          >
        >>          > Many thanks,
        >>          >
        >>          > Mark
        >>          > G0MGX


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