[minima] Re: Parts list spreadsheet, still work in process

  • From: "Mac A. Cody" <maccody@xxxxxxx>
  • To: minima@xxxxxxxxxxxxx
  • Date: Sun, 16 Mar 2014 00:16:22 -0500

It is better to keep the backlight LED on the 5V buss. Placing it on
the 12V buss would require a larger resistor in order to provide the
appropriate current for the LED.  For example, assume the LED has a
typical forward voltage drop of 4.1V for a current of 100mA.  For a
5V supply, the resistor needed for the current would be 9 ohms. The
resistor would dissipate 0.09 Watts of power.  For a 12V supply, the
resistor needed for the current would be 79 ohms.  The resistor would
dissipate 0.79 Watts of power.  Consequently, a physically larger and
more expensive resistor would be needed.  What I would do, though, is
provide a means to switch the power to the LED backlight in order to
conserve power, especially if operating in the field.

73,

Mac AE5PH

On 03/15/2014 11:49 PM, Mvs Sarma wrote:
Perhaps, we can mod the back lit section and connect it to 12V instead. BUT the series resistor should be re evaluated. Thus we can manage 7805 without heatsink on digital board.
On Sun, Mar 16, 2014 at 10:16 AM, Thomas Sarlandie <thomas@xxxxxxxxxxxxx <mailto:thomas@xxxxxxxxxxxxx>>wrote: 

    Just looked at your spreadsheet. One more thing: You have a 78l05
    on the RF board for the KISS mixer bias but you will also need a
    7805 (to220 package) for the arduino board. Make sure you put a
    heatsink on it. The LCD backlight uses a lot of current and that
    regulator needs to dissipate 12-5=7v * the current used by all
    your circuit.

    Do not share the same regulator for both functions.





    On Sat, Mar 15, 2014 at 9:41 PM, Thomas Sarlandie
    <thomas@xxxxxxxxxxxxx <mailto:thomas@xxxxxxxxxxxxx>>wrote:

        Jeremy,

        Great initiative! Some replies in text based on my experience
        building it.

            Hello,

            I've systematically gone through the schematic and made a
            comprehensive parts list from it. I'm hopeful this will be
            useful to both myself and others!

            
https://docs.google.com/spreadsheet/ccc?key=0AkbVpmVim4O7dGM2SGZaYkJvTU1DNnloak1RZnpDZ2c&usp=drive_web#gid=0

            I still have many questions that I want clarification on
            though. If anyone can give more detail about the following
            please reply:

             1. Is there a recommended inductor type for all of the
                filter components? (A toroid type, etc.)


        I have used what Mark recommended and just had to slightly
        adjust the number of turns. Maybe because my magnet wire was
        smaller.

        I thought this information was on my website but nope :( I
        just added it.

        Value   Qty     Core    N-Turns (Mark)  N-Turns (Thomas)
        .33 uH  2       T37-6   10      9
        .39 uH  2       T37-6   11      10
        .66 uH  2       T50-2   12      10
        .78 uH  3       T50-2   13      11
        3 uH    3       T33     25      24


             1. Can the 3u inductor near T3 be the same type as the
                inductors in the filter?

        I guess you are referring to the inductor labelled "RFC" on
        Farhan's schematic. Farhan said: "The RFC is 10 turns on
        FT37-43" According to toroids.info <http://toroids.info>, that
        is 35 uH.

        So no you cannot use the same inductors. And where did you get
        the value 3uH?

             1. What is the 'BAND SELECT' part connected to PD6 and
                PD7 of the Arduino?

        This is a connector that would go to your power amplifier to
        switch different band-pass or low-pass filters depending on
        the band that you are on. The original idea was to use those 3
        bits to select one band (3 bits = 8 possibilities). We have
        since then explored other options and Farhan has chosen the
        CD4017 option.

        Read "Bandswitching the low-pass filters" on the RF386 page
        for more info on the new design that will only take one line:
        http://www.hfsignals.org/index.php/RF386

             1. Can all 4 relays be of the same type? I know nothing
                about relays; what should I be looking for?

        The two relays in the LPF and the relay in the BFO are SPDT.
        The one that switches the audio and tx/rx (bottom of the
        schematic) is a DPDT. You could replace it by two separate
        relays if you wanted to stick to just one model.

        The most important characteristic is the voltage of those
        relays. Get 12v dc relays. They should be adapted to small
        signals. Some are labelled for "RF signals" and are a bit more
        expensive but I am not sure it makes a huge difference for us.

        I have used BESTAR BS-102B for the LPF and the BFO. Bought
        them in a surplus where they were the cheapest 12v small size
        relays. They seem cheap online too:
        http://www.alibaba.com/showroom/bs--102b--12vdc-bestar-standard.html

        For the DPDT I have used OMRON G6H-2.

        You can see pictures of them on my minima webpage.

             1. There are capacitors labeled "0.01" near Q20, but they
                don't have a unit. What size are these capacitors?

        Micro Farads.

             1. There are unmarked electrolytic capacitors. One is
                near Q11; what size are these unmarked electrolytic caps?

        I have asked about those a few times and did not get a clear
        answer. I have read articles that claim that only the "+"
        symbols call for electrolytics and that it is perfectly fine
        to use the curved+flat symbol for ceramics. This matches what
        you see on the schema: the electrolytics do have a "+" sign.

        I have used the same capacitors than everywhere else for those
        (0.1 uF). I would love to hear from Farhan why some have a
        different symbol!

             1. There are electrolytic capacitors labeled +50, are
                these actually 50u?

        Yes. But I have used 47uF. Much easier to find.

             1. There are four 22p variable electrolytic capacitors;
                Are these trim caps? Can I see an example? What am I
                looking for?

        Look on my pictures or mark's pictures:
        http://www.sarfata.org/ham/images/minima-lpf-top.jpg

             1. I see 2 10k trim pots, a 1 turn 10k variable pot and a
                1 turn 100k pot. Is this accurate?

        Yes. You might want to get a logarithmic pot for the 10k
        because it controls the audio but the 100k must be linear.

             1. There is a crystal labeled 16M connected to X2 of the
                Arduino. Is this a 16Mhz crystal?

        Yes.

        Enjoy!

        73,
        thomas

            Thank you very much!
            73 de K2CHA

            --
            Jeremy Chase
            http://twitter.com/jeremychase






--
Regards
Sarma

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