1. I'd like to build the EZ-Tuner, but I'm not very experienced at homebrewing. Should I take the plunge?

The EZ-Tuner is EZ to use, not EZ to build! This is an advanced project and I hope it will only be attempted by experienced builders. Here's why: First, this is not a "plug and play" project. You won't be able to duplicate exactly the mechanical layout, or use exactly the same parts. You will need the improvization skills and inguenity that only come with experience. Second, like all microprocessor-controlled projects, any significant changes in the EZ-Tuner's circuitry or component selection will require software changes. That's why I'm making the annotated source code available. And lastly, this is a long project, that will take months to complete. Inexperienced builders often underestimate the time required to finish their projects (which is why partially completed homebrew efforts are ubiquitous at fleamarkets). I'm not trying to discourage builders, and I don't want to give the impression that one needs to be an engineer to build an EZ-Tuner, but I think a dose of realism and frank self-appraisal is important before you start ordering parts. End of sermon.

6. How much would it cost to duplicate the EZ-Tuner?

The EZ-Tuner is not cheap! The parts cost is about $1500. Roughly speaking, the prices I paid for the major components (some bought at hamfests, surplus outlets, etc.) are as follows:

 Wattmeter (Bird linesection, elements and meter) $450
Cardwell-Johnson variable capacitors (both): $220
B&W 3inch Lexan Coil Stock: $100
Cabinet (Buckeye Shapeform): $179
Printed Circuit Board Fabrication & Parts: $200
BASIC Stamp BS2sx microcontroller: $60
Vacuum Relays (surplus): $50
LCD serial display $59
Misc (switches, wire, hardware, motors etc.) $200

7.Could I build an EZ-Tuner for less money?

Absolutely! I spared no expense on the EZ-Tuner because of my large time commitment and because I could spread the cost out over a couple of years. With a bit of scrounging, you should be able to build one for about $250. It might not look as pretty, but there should be no sacrifice in performance. About the only component you'll have to shell out list price for is the BS2sx microcontroller. Here's a estimated cost range of parts you can find at hamfests, on EBay, or in well-stocked junque boxes:

Wattmeter: $15 -$50
Variable Caps: $10-$75
Coil Stock (or wind your own!): 0-$10
Cabinet: $50-$100

8. Are there any hard-to-find parts in the EZ-Tuner?

The only hard-to-find part is the two-wire 30 degree (12 steps/rev) Ledex rotary solenoid that turns the inductor switch. I found one in a surplus medical imaging amplifier, and see them pop up occasionally on EBay and at hamfests. As I recall, the amplifier was made by E.T.O. in the 80's.

Fortunately, there are many alternatives to the specified item. Surplus Sales of Nebraska lists numerous Ledex and other motorized switches and motor assemblies in their on-line catalog, and many of these should work with a bit of adaptation. Shindengen of America also manufactures rotary solenoids.. Another possibility is to use a stepper motor instead of rotary solenoid. See Question 14 for details.

9. Can I use a rotary inductor instead of a switched inductor?

Yes, but there are some caveats. First, you'll have to be patient while the EZ-Tuner changes frequency, since it obviously takes time to crank a rotary inductor through its settings. Secondly, you'll have to modify the design to use a stepper motor to turn the inductor. This change will require a software modification. Also, you'll have to rig up a limit switch that tells the microcontroller when the inductor reaches its end-of-travel location. Neither task is terribly difficult, but will require some ingenuity. Frankly, I'd stick with the switched inductor. (See my April 2002 QST article for a discussion of the limitations of roller-inductor tuners.)

10. I'm confused about stepper motors, which seem to come in many sizes and number of wires. Which kind should I use and where do I find them?

Stepper motors for the EZ-Tunervariable capacitors are easy to find, but it is important to use the correct type. Here are specifications to look for:

Type: UNIPOLAR (6-wire) Note that 8-wire "universal" motors will also work, but not 4-wire "bipolar" motors.
Rotation:1.8 deg (200 steps/rev) This is the most common type
Current: maximum of 1.1 Amps (the limit of the IC current switches)
Voltage: 5-24 VDC (My motors were rated at 11.2 V, 0.44A.)

Stepper motors come in many sizes and shapes , but fortunately sizes are standardized. I used size NEMA 23 motors , which have enough torque to turn the variable capacitors. All NEMA 23 motors use the same mounting hole pattern, and most have 1/4 inch diameter shafts. NEMA 34 motors are larger, with 3/8 inch shafts, and obviously these will work also. Some stepper motors have dual shafts (front and rear) and these are preferable because you can use the rear shaft for the limit detect wheel. EBay always lists many stepper motors (I bought mine there for about $15 each). Many electronics outlets also sell surplus stepper motors(Jameco, Marlin P. Jones Associates, All Electronics, etc.)

11. What tools and test instruments do I need to build the EZ-tuner?

In addition to ordinary hand tools, I used a band saw, drill press, chassis punches, belt sander, sheet metal brake and a sheet metal shear to build the EZ-Tuner. The chassis punches, brake and shear made life easier, but aren't really necessary.

The circuit boards were designed using "Circad 98" (download a free evaluation version at http://www.holophase.com), and the controller circuitry was tested and debugged using a DVM, a signal generator (HP 8640B) and an oscilloscope (TEK TDS-420A). I also used an MFJ-259B impedance andalyzer, an Autek RF Analyst model RF-1, and an AI1H Resistance Substitution Box to set the inductor taps. You wouldn't need all this test equipment, since you'll be dealing with a proven design, whereas I was starting from scratch. Also, part 3 of my QST article (June 2002) describes a way of setting the inductor taps that uses only a 50 ohm dummy load and a transmitter with extended frequency coverage. Lastly, you'll need a computer with a serial port to upload the software to the EZ-Tuner.

12. How difficult is it to load the software into the EZ-Tuner Microcontroller?

It is very easy and requires no special equipment. First, connect the EZ-Tuner programming port to a serial port on your PC, using an ordinary serial cable. Then, download the free Basic Stamp editor from http://www.parallaxinc.com to your computer. Next, download the EZ-Tuner software and save it as a file on your hard drive. Finally, using the Basic Stamp editor, open the file, click on "RUN," and the software will be loaded instantly into the EZ-Tuner. You use the same procedure to modify or update the software.

13. How about software upgrades? Will you make them available?

The software for the EZ-tuner is freely available to all, and users are encouraged to improve the code. I'm sure that others will come up with good ideas and be able to make significant enhancements. I'll post revisions and upgrades on this site, as they are developed.

14. Can I use a stepper motor instead of a rotary solenoid to turn the inductor switch?

Yes. In fact, a stepper motor will make for faster and smoother operation, because it turns both in the CW and CCW directions, whereas a rotary solenoid only turns in the CW  direction, (Thus, 1 CCW step of a solenoid requires 11 CW steps.)

If you plan to use a stepper motor, however, note that its steps must be compatible with the inductor switch indexing. Thus, you can't use a common 1.8 degree stepper motor, because a 30 degree indexed switch is not an integer multiple of 1.8 degrees.

One option is to use a 9-position 36 degree indexed switch and to eliminate two of the minimally used taps on the coil. Then, 20 motor steps of 1.8 degrees each would advance the switch exactly 36 degrees, or one position.

A second option is to use a common 7.5 degree stepper motor, since 4 steps would give exactly 30 degrees. Two possible candidates (I haven't tried them, so make sure they're unipolar types) are sold by MECI (http://www.meci.com) and are listed on their website. The specifications are:

Motor #1: (MECI Part No. 420-0046 @ $3.49/ea) - 7.5 degrees, 5VDC/3.5 ohms
Motor #2 (MECI Part No. 420-0144 @ $1.25/ea) - 7.5 degrees, 12VDC/17.5 ohms

A third option is to gear down a common 1.8 degree stepper motor, so that with multiple steps it will give any desired switch indexing. This is actually quite easy to do. Check out my new "Stepper Motor Hints" page for details.

And . . . all else fails, you can always use a d.c. motor with a gearhead reducer to turn the switch. Small gear-reduced surplus motors are readily available.

15. Can you supply construction drawings, or at least give some of the internal dimension to make it easier to copy your layout?

Sorry, detailed construction drawings aren't available, but here are a few key measurements to get you started:

(1) Cabinet: 17"W x 7"H x 16"D. These are outside dimensions. The inside dims of the Buckeye cabinet are considerably smaller. (See the bulletin board/discussion group page for more details.)

(2) RF compartment: 16"W x 4.875"H x 14"D (inside dimensions)

(3) Chassis-plate-to-front-panel-gap: ~2" from chassis front edge to inside front panel (not criticall

(4) RF Compartment & Chassis Vertical Clearances (top to bottom):

Afew additional comments: First, I recommend using my measurements only as a general guide. There's no substitute for laying out the actual components to make sure everything fits. Second, if you use longer variable capacitors than my specified Cardwell-Johnson types, you'll probably have to use a deeper cabinet. There isn't much extra front-to-back clearance between components. In fact, when you're laying out the front panel, make sure the back of the meter, encoders, and pushbutton switches don't bump into the stepper motors. I made a scale drawing of the front panel with "shadow" outlines of all the parts to make sure that two components didn't try to occupy the same space! And finally, unless you're wedded to my particular cabinet (which, admittedly, is a beauty), then you might want to use a slightly larger cabinet. You'll save design time if you don't have to plan for a tight fit.

16. Is it desirable to use sockets for the IC's on the EZ-Tuner circuit boards?