Six Digit LED Frequency Display for the:

Heathkit SB, HW, HR Series

Kenwood TS-520(S / SE)

Heathkit SB-104 / 104A 

Yaesu FT-101 Series - Available NOW

dfd2 upgrade  

1. Introduction

    The PCB (and the software) have been redesigned to allow a 6 digit LED display (TM-1637 chip - controlled serially by the PIC processor) to be used.  Jumpers (options) on the new board allow the design to serve the Heathkit family of radios, the Kenwood TS-520S / SE, the Yaesu FT-101 and (later) the Collins radios.  It can also be used as a simple frequency counter. Thus far, the code has been written for the Heathkit and Kenwood TS-520 radios and for the Yaesu FT-101 family.   

Note: Bare-bones boards with pre-programmed PIC processors are available for others who might like to build one.

Also Note: The main thing to remember about this display is it's inherent and consistent accuracy.  As it constantly measures the frequencies of the HFO, BFO (Carrier Oscillator) and VFO the display is always smack on even were one of the oscillators were to drift slightly.  This is a step above some of the other frequency displays (like the Yaesu 601B) that measure just the VFO frequency and then compute a result based upon previously customer-entered frequencies.  There are no switches for band or for mode selection.  It just transparently works.

This website will first show how how to build and test the board and it includes references to the Mouser parts used.  Later sections show how to interface it with the desired radio.  

If you are interested, then please read on.
 
2. Design and Schematic - Phase 4 Board (Current)

   P/C board design:
3. Construction Details (read on down)
1) Refer to the printed circuit board layout and to the schematic as you procede.  Mount components on the silkscreened side of the board:

Important Suggestion - when soldering the pin headers (next step), you might first want to first place them in a spare integrated circuit socket or in a female header pin set (usually available on eBay).  This way, the heat of your soldering iron will not melt the plastic and cause the pins to seat unevenly.  I've soldered hundreds of pins this way and it always works.    

2) Mount the Pin Headers on the board . Note: no need to install PICKIT3 header or resistor R4 as they are used by me only for in circuit programming:
3) Install three (3) 16 pin sockets for the HFO, VFO and BFO (CD74HC4046).  The notches point towards the inside of the P/C board.  Solder carefully.  Follow the silkscreen patterns.
          4) Install the 16 pin IC socket for the CD74HC153 with the notch pointing toward the bottom of the board. 
5) Install the 18 pin IC socket for the PIC16F628A microprocessor with the notch pointing toward the bottom of the board.
6) Install the (9) .1mf ceramic capacitors. (C2, C3, C4, C5, C9, C10, C12, C13, C14 )
7) Install  C6, C7, C8 -.01 mf ceramic capacitors,  80-C324C103K3G5TA
8) Install the (6) 1N4148 input protection clamping diodes  (component names not marked on board) for the HFO, VFO and BFO
9) Install R1 (100 ohms), R2 (1K ohms) and 3 (1K ohms) - all 1/4 watt resistors). 
Also Note:  R3 on the PCB is not used in this design so you'll have to jumper it with a 30 gauge wire.

10) Install the polarity reversal protective diode D7 (1N4001, or equiv), 
11) Install C1, C11- 10 mf elecrolytic capacitors (watch the polarity and soldered connection spacing),
12) Install the 5 volt voltage regulator (LM7805)  - IC-7
13) INITIAL POWER TEST - Apply 13 VDC to the power connector and verify that +5 VDC is present on pin 14 of the microprocessor socket, on pins 15 and 16 of the CD74HC153 socket, and on pins 16 and 3 of  each CD74HC4046 socket.  REMOVE THE POWER and verify that ground is present on pin 5 of the microprocessor, on pins 1, 8, 10, 11, 12, 13 of the CD 74HC153, and on pin 8 of each CD74HC4046 socket.  Leave the power off until step 17.

14) Install the 4 pin 'canned' crystal oscillator (Mouser - 520-2200BX-200).  This is a 4 pin DIP and it must be properly installed.  Pin #1 of the oscillator has a pointed edge.  Here are some pictures showing how to orient the package before soldering it - pin1_1      pin1-2     pin1_3.
15) Referring to the printed circuit board layout, install the integrated circuits by straightening the pins (rolling them on a hard surface) and then my 'rocking' them in.....noting  their orientation.  If you encounter any resistance check it out before proceeding.   New integrated circuit sockets sometimes offer insertion resistance the first time they are used.
16) Wire the 6 Digit LED Display (available on eBay, Amazon.com and Walmart for under $10).  Pick your desired color and be sure it has a TM-1637 serial controller.  They come with a 4 pin wire wrap connector that must be soldered to their backplane, as shown here.  Four (4) connections need to be made for Power VCC (+5VDC), Ground (GND), Digital I/O (DIO) and Clock (CLK) - as shown in the schematic.   Double check to ensure that you have made the right connections (especially VCC and GND) before powering it up.
17) Power up your board.  Since it will not be connected to a radio, you'll see a negative number similar to F1572.22 . until the display has been connected to your radio's HFO, BFO and VFO points.
If you find that the display is too bright for your liking (most probably only on WHITE displays), you may tone it down a bit by shorting the DIM pins on the board.  Since the unit has been programmed to update the display ONLY WHEN the received FREQUENCY HAS CHANGED, you may not see the display change immediately.
4. Heath SB-300 / 301 / 303 / 313 / Kenwood TS-520S

    Using 2 to 3 foot lengths of RG-174 (or equivalent), install PHONO plugs on one end and and solder the other end to the HFO, VFO and BFO DDS VFO P/C board connection points.  Either tag or color code these connections and insert them into the SB-300, SB-301, SB-303 (etc).  Jacks are on the radio's rear panel.  These are the easiest interfaces.

    Note:  For the SB-303 place a 47 ohm resistor across the VFO coax connection from the radio to the DFD-2.  If this resistor is not placed, the frequency display may become intermittent.

    The Kenwood TS-520S HFO, VFO and BFO plug-in connections are on the rear panel ( rear mounted jacks).

    Power (12VDC) can be suppiled via an inexpensive wall-wart and / or is available from the radio itself (TS-520S)  Good luck on finding the original GD-5 plug that powered the Kenwood DG-5 digital display.  Small female jacks can readily be installed on the TS-520S rear panel to provide a source of fused 12VDC for your counter - just attach the lead to the DG-5 connection points.

5. Heath SB-100 / 101 / 102 / HW-100 / 101 

    CAUTION: - if you are unsure, unfamiliar or unable to work safely within a tube radio where potentially lethal voltages lurk, please don't consider this product unless you have a competent and experienced helper with you.  I will not be responsible for any harm to either you or to your radio as a result of attempting this conversion.  If you have any doubts - don't try it or check with your 'Elmer'.
6. Heath HR-1680 

7. Heath SB-104(A)  

        Not Required! - an inexpensive 6 Digit Digital  Frequency Counter available on eBay can nicely fulfill this need

8. Enclosure Suggestions - Express Yourselves!

    Selecting a suitable, functional and reasonably attractive enclosure is a matter of personal choice and handcrafting ability.  I'm not terribly dextrous when it comes to ccrafting items like this one, but I did build a couple of enclosures whose details I'll share with you.

    For one enclosure for a TS-520S, I used a small plastic clamshell type of enclosure found on eBay.  I used a piece of plexiglass (Lowes) as the front panel and mounted the 6 digit LED unit on its rear - looked reasonably OK. Since it was physically light, I added a couple of  flat electrical box covers (from Lowes) inside  to both weigh it down (so it would not move on my desk) and to provide a heat sink for the voltage regulator.  The regulator does not get all that hot, but inasmuch as I had installed the flat electrical box covers beneath the board for weight I decoded to use it as a 'sink'.  I had some spacers from another radio that I had cannibalized, so I used those.  (Simple 4-40 machine screws, washers and nuts would have worked just as well.)  

   The 6 digit LED is mounted on the front along with an OFF - ON power switch on the rear panel.  The power connector, 3 RCA inputs and an optional switch to activate the counter feature are located on the rear panel.  I put sticky feet on the bottom.  I'm sure that those of you with better mechanical skills could whip up something a lot nicer.

   For another enclosure (for the FT-101) I used a small metal clamshell enclosure from Amazon.  It has metal covers on the front and rear.  I cut a piece of plexiglass to serve as the front cover and carefully drilled holes in the 4 corneers to match up with he openings in the cabinet.  The LED display itself mounts on the inside of the plexiglass held in place by 2 flat-head screws drilled thru to the plexiglass.  The printed circuit board is mounted on spacers within the box which is also used as a (rather generous) heat sink.  A couple of ventilation holes were drilled in the botton and top. Stick-on rubber feet keep it stable on top of the radio or on the operating desk.  Since the box is heavy metal, there's no need to weigh it down.

   Also, Mouser sells some interesting enclosures that would also fit the bill.  Here's just one series: http://www.busboard.com/documents/datasheets/BPS-DAT-(BOX2-P14)-Datasheet.pdf  You'll want to get one that has removable front and rear covers.

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9. FT-101 Radio Family Interface  - self contained and ALWAYS accurately reflects the CLARIFIER, BANDSWITCH, VFO and MODE settings! - New!

    a) The DFD-2  - A Time Proven Design Applicable to Several Radios

    Neil Hecht (SK) was the genius who founded www.aade.com.  He cleverly designed many products including digital displays for many of contemporary analog radios including the DFD-2 solution for the Heath SB series and many other rigs.   I used the essence of his hardware design and wrote my own hand assembled code not only for my original DFD-2 (both LCD and 6 digit LED interfaces) but also for the FT-101 version.  This required some significant changes to acommodate the FT-101 frequency conversion scheme.  The software simply reads, 'massages' and outputs an accurate digital display only when the computed frequency actually changes.  This way, needless circuit noise is eliminated.

    The Heathkit (SB-300 / 301 / 303) and Kenwood (TS-520S / SE) radio designers provided rear mounted HFO, BFO and VFO signal pick-off points providing an easy inteface to the DFD-2.  Yaesu did not do the same as they apparently had no plans to equip their radios with digital displays 'back in the day', mainly because (I assume) popular, easily programmed processors like the Microchip PIC  and Freescale's HC05 / 8 series were not available then.  Heath used them to provide true transceive operation with their matching SSB transmitters (SB-400 / 401) and Kenwood was apparently more foresighted with a true, outboard digital display in mind.

    On his website Neil offered plans to interface the DFD-2 design with the Yaesu FT-101 series. Iinterfacing is a bit move involved as RG-174 miniature coaxial cable needs to be run withn the radio to the circuit boards providing the VFO, HFO and BFO (Carrier Oscillator) signals.  Each lead is connected to the points shown below through a small capacitor and then run to the rear panel for connection to the DFD-2 proper.. Three signals (HFO, BFO (aka Carrier Oscillator) and VFO) need  to be routed to the DFD-2 unit itself.

    b) Connecting the DFD-2 to the FT-101 Radio - Three Possible Options

    These signals can be 'picked' off points on various circuit boards and then run to connection points on the FT-101's rear panel. Here are some connection options including the one that I used::

1. Repurposing the Existing Rear RCA Jacks - Somewhar Challenging

    One could 'repurpose' 3 of the existing RCA jacks  in the center rear of the radio).  They are labeled AF IN, IF OUT, SPEAKER, PTT, PATCH, REC, TONE, A-TRIP.  The target jacks themselves must be physically replaced because they are old with their inside them brittle (connections soldered to them are subject to breakage should the inserted RCA phono plug be twisted).  

    After deciding which of the 3 functions you plan to sacrifice, you'll find that removing these RCA connectors with a small socket is virtually impossible because the Yaesu techs soldered the coax shield connections to a central ground 'spine'. The solder blobs interfere with the socket wrench so one must remove the whole panel (two screws).  Ideally one should be able to remove the whole panel from the back of the radio to service it, but regrettably there is very little slack in the wiring to permit this.  So, you must sever all of the connections (except for the external speaker connector which unscrews) and sever the heavy wire that connected the 'spine' to the chassis.  

    Once done, the whole panel can be removed and the desired 3 RCA connectors replaced with 3 new RCA connectors to which the appropriate lengths of RG-174 coax will be connected for the VFO, HFO and BFO (Carrier Oscillator). IMHO, the only one signal worth reconnecting would be the external speaker which screws back in and is grounded to the chassis along with the 'spine'.  Finally, the unconnected  severed leads should be removed (not just taped) lest they other problems later on - the schematic shows their connection points within the radio.  Have fun - I did!.  Go To Picking

2. Repurposing the External VFO Connector - Relatively Easy

     I replaced the rear panel octal External VFO socket with a small piece of grounded printed citcuit board materail on which 3 RCA phono jacks (with ground lugs) had been mounted.  These would become the connection points for the HFO, BFO and VFO. Ideally, this should be mounted inside the chassis for a more professional appearance. I prepared three (3)18 inch lengths of RG-174 with a male plug soldered to each end to connect radio to the display proper  If you decide to do your coversion this way be sure that the RCA jacks are securely tightened to thie piece of metaal or printed circuit board (I used some Crazy Glue just to be sure they would not twist..
  3. Mounting the 3 Jacks on the Rear Panel Adjacent to the Regulator Board  - Untried as of yet - Requires Drilling - Tempting.............

    When the Regulator board is removed there appears to be enough space on the back panel to mount the 3 RCA jacks, running tye coax leads thru the existing grommet..  I suppose that this could be done were one very careful, taping over the open sockets while providing ample pieces of heavy duty tape to also catch any metal filings.  But, this would keep me personally awake at night.  Anyone brave enough to try it???
                Note:  Tag the rear panel connections after you have made them.  If you forget which is which, just turn the radio on and  measure the output of each with your digital meter or a suitable freqjuency counter.  The
    c) Assembling the DFD-2 Circuit Board

             Note: Before starting with the conversion ensure that your FT-101 is working properly.  Especially check the 6 volt source and the frequwncy setting trimmers on the modulator board for accuracy.  If the 6 volt siurce is hard to adjust or drifting over  time you might want to convert the regualtor to an LM-7806....relatively easy to do.

    Follow the instructions on this webpage to build the DFD-2 board itself.  All the parts are listed with the latest parts and a Mouser Electronics parts list (see above).  

Also Note: The only changes are that the input resistors for the VFO and BFO are changed from 1K to 100 ohms.  This reduces any unnecessary loading on the FT-101's BFO and VFO circuitry.   

    d) Packaging the PCB and LED Display

    I strongly recommend that a metal box be used to house your display and LED.  While I purchased mine on Amazon (Eightwood Aluminum Enclosure Electronic Project Box Case DIY 3.94 x3.94 x1.97 inch (LWH), there are undoubtedly others eleswhere - like on eBay -that would suffice..  The PCB is mounted inside the box on standoffs - the box also serves as a heat sink for the LM-7805 voltage regulator.  Some holes are drilled on the top for ventilation purposes, stick on heet are provided on the bottom, and RCA phono jacks are mounted on the rear along with an OFF - ON switch.  The metal box nicely attenuates any electrical noise from the box while the rear panel provides a uniform ground for the shields of the 3 coaxial cables terminated there. For the front panel I traced a piece of Plexiglass (Lowes) which is easily cut, sounded the corners with my wife's nail file, and used some black tape on the outside from which Icarefully removed a portion for the display to shine thru.

    Note: As mentioned before, it's very important that the shields from the 3 coacial cables be consistently grounded - near the pick off points, at the rear panel mounted RCA jacks and at the display, proper.  Likewise, the shield connections at each of the 6 RCA pluds must be carefully soldeded.


    e) Radio Connections

    You'll have to prepare three (3) cables (RCA plugs on both ends) to connect the rear mounted RCA radio jacks to those on the display.  Try to limit them to 18 inches - or less.  This is to limit the loss within the and to ensure a consistent display output.  Using the 100pf 'blocking' capacitors (instead of the .01 mf units recommended by Neil reduces the coupling between the radio and the display and also the signal loss within the radio.  So far, it's worked fine for me.

    Important Note:  You'll most probably have to make up your own cables as the ones sold on eBay for VCR use are just too lossy.

    f) Display Power Supply Considerations

    I had originally planned to use a power source within the FT-101 for the display but was later reluctant to use the 12 VAC filament winding as a source of AC for a new, inboard internal DC rectifier(which would obviously have to be fused - requiring tet another rear panel hole).   So, I used a wallwart Type device.  I you go this route you might try to find a wall wart that uses a transformer driven one as these are more electrically 'quiet'.

    g)  Operational Aspects
        Note:  You may notice the display changing when you are transmitting - this does not affect the output frequency or purity of your signal - just the displayed signal.  This may be caused by transmitting into an antenna with a high SWR, an improperly grounded  transceiver, or missing grounds on any of the coaxial cables installed for the DFD-2.

    h) Other Considerations
     i) Birdies - Ckeck Your Coiaxial Cable Grounds

    Now even radios designed with integral digital displays will evidence some birdies and artifacts when not connected to an antenna and this conversion is similar in that regard.  However, with an antenna connected and the preselector properly tuned  the only birdie I've noticed is around 14.167.  Most potential birdies can be either outright eliminated or severely attenuated to the point where they are masked by normal band noise by properly connecting the coaxial cable shield wires and ny using a metal enclosure for the LCD / control board.

    j) Possible Subsequent Enhancements

  A smaller 6 digit LED display could be used and mounted within the radio in the space where the current analog dial resides.
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10. Radio Service Manuals & Schematics

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