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 Soon

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). 
Note:  R3 on the PCB is not used in this design so you'll have to jumper it with a 30 gauge wire (may already have been done - please check).

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  (like prom night?).
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 inexpensice 6 Digit Digital  Frequency Counter available on eBay can nicely fulfill this need

8. FT-101 Family Interface  - self contained and ALWAYS accurately reflects the bandswitch and mode settings!

    Interfacing the DFD-2 to a Yeasu radio 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 .01 mf capacitor and then run to the rear panel for connection to the DFD-2 proper.  More on this below.

a) Connections and cabling options (pictures have been provided):

1)  You may use the REMOTE VFO PLUG (easiest option) if you:

2)  You may install RCA chassis mount jacks on the rear panel if you:

b) Yaesu FT-101 signals - there are 3 of them.

   The BFO signal may be tapped in either of two different places.  It appears on pin 6 of board 1184A (MODULATOR UNIT) and is carried by a short piece of coaxial cable to pin 5 of board 1183A (LOW FREQUENCY IF BOARD).  Each board has a convenient grounded pin for shield connection, but board 1183A is easier to reach with a small soldering iron.

   After routing the RG-174 from the rear panel to the area of  the board chosen,  solder a .01 disk ceramic capacitor to the center conductor of the cable.  Then solder the free lead of the capacitor to the chosen pin of the board edge connector and the shield to the nearest grounded pin on the edge connector.

  The HFO signal  is available at the test point near the top edge of board 1181A - (HF UNIT)  - install the blocking capacitor (.01 disk ceramic) on the board between the test point and unused pin 15.  This will allow easy removal of  board 1181A.  However,  it requires soldering the coax to the edge connector for board 1181A in a very congested area.  In this alternative installation the cable stays on the underside of the chassis and is soldered to pin 15, with the shield is soldered to pin 18 of the edge connector for board 1181A.

    The VFO signal is available at pin 11 of board 1180A (HIGH FREQUENCY IF UNIT).  After routing the cable from the rear of the chassis, solder a .01 disk ceramic capacitor to the center conductor.  Solder the free capacitor lead to pin 11 and the shield to pin 10 of board 1180A.

9. Enclosure Suggestions

    Selecting a suitable, functional nd 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.  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 4 flat-head screws crazy glued 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.

10. Radio Service Manuals & Schematics

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