Dave Richards AA7EE

June 27, 2011

The N3ZI Digital Dial

The last 2 QRP radios I built were the Fort Tuthill 80 and the Norcal 2N2/40, both of which I fitted with KD1JV digital dials. I’d seen Doug Pongrance N3ZI’s Digital Dial and was curious, as it drives an LCD display, as opposed to the LED display in Steve Weber’s kit. I figured that it should draw less current and as such, would work well for QRP rigs operating from battery power. That wasn’t quite what I found, though the N3ZI Digital Dial does have other advantages.

The counter comes as the PCB and a small bag of parts packed in a small box.  Doug does sell a serial LCD display to go with the counter, but there are many cheap displays sold on eBay that will also work with this counter. I chose to go the latter route, as I wanted a display that was the same size as the counter board, and Doug’s display is much longer. When ordering the counter kit, you can also order a hardware kit to fix the display to the counter board, if you’re going to use a display of the same size. There are full details at N3ZI’s site that explain what types of LCD his two boards (the full kit and the super kit) will drive.

I bought a nice display with yellow backlight from a vendor on eBay called electronics_lee for $4.80 including shipping from China. Even better, was that instead of the 3 week timeline that eBay gave me for delivery, the display was in my mailbox in just 6 days (5 business days) from the date of ordering from China – and all for $4.80 including shipping from China. Actually, Doug’s LCD is cheap also, it was just that I wanted a smaller one.

It goes together easily, and here’s what the whole thing looks like. In this first shot, you see more of the display I bought from eBay than the N3ZI board:

Here’s the flip-side, showing the counter board. If you want a lower profile, you can mount some of the components on the other side of the board, and mount the crystal horizontally. I just built it “stock”.  Visible are the 2 micro switches that are used to program the IF offsets into the board (it can accommodate up to 9) and to select them when the dial is in use. On the right at the front is the trimmer pot for varying LCD contrast, on the right-hand side near the back is the (black) power jack, and behind the regulator is the signal input jack (white and partially obscured by the regulator):

In this shot you can clearly see the short wires I used to connect the 2 boards.  You can use header pins and a ribbon cable if you want, but this seemed unnecessary, as I don’t expect to be disconnecting and reconnecting the display.  One thing that did offend my slightly OCD sensibilities was that the insulation on the wires I used melted readily when exposed to heat, and you can see the result.  Aaah well, I have to learn to control my inner desire for perfection, or I’ll never get any experimentation accomplished:

Compared to the KD1JV Digital Dial, which is a favorite for many QRP’ers wanting to add a frequency display to their radios, it is quite large. Here’s a comparison shot of the N3ZI counter on top of my Fort Tuthill 80 fitted with the KD1JV Digital Dial:

The full counter kit from N3ZI can supply current for a backlit LCD as well supplying either a +ve or -ve voltage for the display contrast (some LCD’s require a -ve voltage). It’s pretty much a full-service kit to drive most LCD’s. Add to that the fact that you can program in up to 9 different IF offsets including an offset of zero for use as a straight frequency counter, and you have quite a versatile counter for the shack.Two things that I like about the N3ZI counter are

1)        The IF offsets are programmed in manually using the switches – you don’t have to feed it a squirt of RF. You can do this with up to 9 different IF offsets and,

2)        Instead of a trimmer capacitor to fine-adjust the crystal for optimum accuracy, you can calibrate the counter in software using the micro switches.

Comparing KD1JV’s Dial with the N3ZI one again, I measured a current draw of only 20mA on the dials in both my Norcal 2N2/40 Tut80), and with the LED display switched off, which is achieved by holding the control button down for a little over a second, the consumption was just 7mA for both units.  My N3ZI Dial consumed about 34mA with backlight and 18mA without.  The backlight on the display was quite bright, so I increased the value of R3 (the resistor on the N3ZI board that supplies the backlight current) to 100 ohms whereupon the current consumption decreased a little to 28mA with little noticeable decrease in the the brightness of the backlight. All the preceding current consumption measurements for both units were made at a supply voltage of 13.8V.

So what’s the upshot of all this? Well, current consumption differences (which are minimal) aside, I see these main differences:

Programmability – in order to program an IF offset into the KD1JV Digital Dial, you have to feed it with RF at that particular frequency while the counter is in program mode. To program it with a different offset, you would have to follow this procedure again.  You can program an offset into the N3ZI Digital Dial directly with the micro switches, and can do this for up to 9 different offsets, all of which can be selected by the micro switches during use. If you mount the dial in a case, panel mounted buttons can be employed

Size – if space is at a premium, the KD1JV Dial is the one to go with. N3ZI’s counter does take up more space, though it offers more features (albeit with a little more current consumption if you’re using a backlight)

Anti-jitter – The N3ZI Digital dial contains anti-jitter code so that the last numeral doesn’t constantly flicker between 2 adjacent digits, which the KD1JV dials sometimes does

As for me, I’m leaving the KD1JV Dials in my 2 rigs – they’re small and the current consumption is low, but am pleased as punch with the N3ZI Dial as a general counter and digital dial for the shack.

NB – In it’s standard configuration, the N3ZI Digital dial covers 1 – 45MHz but the coverage can be extended above and below that by changing a jumper on the board.

EDIT – I just received this e-mail from Doug N3ZI with some useful information on his counter:

Thank you for the unbiased review and positive comments.

I do have some comments regarding power consumption.  You reported 18mA,  I would expect a few mA less.  But it depends on exactly what VFO  frequency is input, and exactly what LCD is being used.   But one can get much lower power, ~5mA, by powering it off of a 3.3v battery, rather  than the 5v regulator, and without a prescaler.  It will count up to about 8.5MHz in this configuration so it’s OK for a 80M or 40M DC radio.

The micro just checks the frequency occasionally, and if it’s the same as the last reading, it goes to sleep without updating the LCD.  The micro draws about 40% extra power for a few seconds after power up, and
for a few ms when the frequency changes.  But if the prescaler (divider) chip is used and connected to the radios VFO, it will run all the time,  and thus continuously draw 1-3mA depending on the VFO frequency.

If someone is looking for a low power backlit display, the Blue/White ones being sold on ebay are very readable with backlight currents in the 5-10mA range.  And there are some much smaller LCD available in the 8×2
format.

Again, thanks for your report.

73, Doug, N3ZI
http://www.pongrance.com/

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2 Comments »

  1. Will you be offering the counter with I.F. offset again as a complete kit and do you have access the metal tube shield plus preamp for the use of coupling signal from the Local Oscillator tube?
    Thanks, Ken

    Comment by Ken — February 25, 2016 @ 6:48 pm | Reply

    • Ken – you’ll have to ask Doug N3ZI about that. I’m just a happy customer who bought this digital dial from him nearly 5 years ago, and blogged about it.

      73,

      Dave
      AA7EE

      Comment by AA7EE — February 25, 2016 @ 7:33 pm | Reply


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