[minima] Re: Linear Output Filter Switching

  • From: Mark G0MGX <mark.g0mgx@xxxxxxxxx>
  • To: minima@xxxxxxxxxxxxx
  • Date: Tue, 04 Feb 2014 06:53:33 +0000

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 (5MHz).

    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 stop-band.
    > 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 designs.
    > 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
    > maybe with the tubes others are suggesting! I've never built
    > 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
    >> 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 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
    >>      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 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
    >>      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 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
    >>          Wayne NB6M
    >>          > On Jan 31, 2014, at 1:24 PM, Mark G0MGX
    >>          <mark.g0mgx@xxxxxxxxx <mailto: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
    >>          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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