[minima] Re: Linear Output Filter Switching
- From: Wayne McFee <nb6m@xxxxxxx>
- To: "minima@xxxxxxxxxxxxx" <minima@xxxxxxxxxxxxx>
- Date: Sun, 2 Feb 2014 10:51:03 -0800
Mark,
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> 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.
>
> Mark
> G0MGX
>
>> 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
>> Mark
>> G0MGX
>>
>>> On 01/02/2014 18:24, mpcharlton@xxxxxxxxxxx wrote:
>>>
>>> Mark
>>>
>>> Have a look at this halfway down the page...
>>>
>>> http://www.vk5tm.com////homebrew/filter/filter.php
>>>
>>> Mark
>>> G6ZQS G-QRP 2247
>>>
>>>
>>>
>>>
>>> -------Original Message-------
>>>
>>> From: Mark G0MGX
>>> Date: 01/02/2014 17:29:09
>>> To: minima@xxxxxxxxxxxxx
>>> Subject: [minima] Re: Linear Output Filter Switching
>>>
>>> Isn't this:
>>>
>>> http://www.g3ynh.info/digrdout/74141.html
>>>
>>> exactly what we need to go from Binary outputs on our 3 digital lines to
>>> individual relays controlling filters?
>>>
>>> Mark
>>> G0MGX
>>>
>>>
>>> On 01/02/2014 15:26, 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<minima@xxxxxxxxxxxxx>
>>> > Reply-To: 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 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>> 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:
>>> >>
>>> >> http://tronixstuff.com/2011/08/26/tutorial-maximising-your-arduinos-io-ports/
>>> >> 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.
>>> >>
>>> >> http://tronixstuff.com/2010/04/30/getting-started-with-arduino-chapter-four/
>>> >>
>>> >> 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>> 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
>>> >> construction!
>>> >> >
>>> >> > Many thanks,
>>> >> >
>>> >> > Mark
>>> >> > G0MGX
>>> >>
>>> >>
>>> >>
>>> >
>>>
>>>
>>>
>>>
>>
>
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