0312038.pdf

By Dale Botkin, NØXAS

The PicoKeyer —

An Ultra Low

Power CW

Memory Keyer

NØXAS redefines “low power” for us with a keyer that

draws 4 nA (that’s 0.004 microamperes!) at idle.

tive on the HF bands, I have used

various electronic keyers with a

Vibroplex paddle. While I have spent time

operating with a straight key, I have never

really enjoyed it or gotten good at it. I have

used built-in keyers in several brands of

gear, including a few from well-known

low-power kit manufacturers. All have

worked well…some better than others.

I recently had the opportunity to up-

grade my home HF station to a Kenwood

TS-930S/AT. While I enjoy the rig, it

lacks an internal CW keyer—so it was

back to the straight key. I felt sorry,

frankly, for some of those operators on

40 meters who were subjected to my fist

during those first few weeks. I wasn’t

getting better, and I decided it was time

to go back to the paddle and the keyer.

Being a hacker at heart, however, I wasn’t

going to go out and buy what I could build

in an evening! I decided I would build a

very simple, barebones keyer to do noth-

ing more than generate dots and dashes

with proper timing and spacing. Like

many other projects, this was a good idea

until it got out of hand.

I knew I had all the parts I would need.

One of my hobbies involves building

projects with embedded controllers,

mostly using Microchip’s PIC proces-

sors. 1 For me, the perfect project is one

that involves an absolute minimum of

parts. First of all, I like to be able to build

without ordering anything, and my “junk

box” is pretty well stocked, but it doesn’t

have everything. Ideally, I like to use a

small microcontroller with as close to

zero external components as can be

achieved. I am also a big fan of design-

ing for as little current consumption as

possible, mainly because I don’t like

changing (or buying) batteries and be-

cause power supplies are always a pain

to build. I guess I’ve gotten lazy in my

old age, but it does make for some inter-

esting design challenges!

run on not much more than a cool breeze.

The hardware design was the simple

part, requiring nothing more than connec-

tions from the key to the PIC and a single

transistor to key the rig. I added the SPST

pushbutton switch and decided to use one

pin for an LED during debugging, leav-

ing one pin unused. I assembled the

project on a solderless breadboard and

wired up the paddle. Now came the tough

part—the software—the heart of the

project.

One of the first steps was to determine

the timing to be used when sending Morse

code. An hour or so of reading various

pages found with a simple Internet search

and I had the “magic numbers” needed to

determine the dot and dash timing for any

given code speed. A couple of hours of

programming later and the chip was gen-

erating properly spaced code from 5 WPM

to as fast as I could send, with the upper

limit set at 60 WPM. The next step was

to add a setup mode for changing the code

speed. While I was at it, I added functions

for setting the weight and selecting Mode

A or Mode B timing.

When I was reasonably satisfied with

the performance, it was time to move

from the solderless breadboard to a “real”

setup and try it out on the air. I used half

of a small RadioShack perfboard and

wired it up as a prototype assembly. On-

air results were good, but there were a

few key things still missing.

The project took on a life of its own

The Design

I wanted to use nothing more than one

chip for the keyer, with a single push-

button for any features that got added

along the way. I also wanted to play with

one of the latest 8-pin designs from

Microchip, the 12F629. These little pro-

cessors cram a lot of features into a very

small package! 1024 words of program

memory, 64 bytes of RAM, 128 bytes

of nonvolatile EEPROM, interrupts,

counter/timers, an internal oscillator, an

analog comparator, and more. The

12F675 shares the 12F629’s features and

adds a 10 bit, four channel analog to digi-

tal converter. These chips are a major leap

ahead compared to the older 8 pin

12C5XX-type devices and their power re-

quirements show it as well. The new pair

will operate down to 2.0 V, and their

SLEEP mode lets them power down and

1 Notes appear on page 40.

From December 2003 QST © ARRL

F or most of the time I have been ac-

over the next couple of weeks. The LED

was replaced with program-generated au-

dio sidetone that could be turned on and

off, and I managed to find a tiny speaker

with low enough current requirements to

drive directly from one of the PIC pins. I

added message memory, beacon mode

with variable repeat delay, then variable

pitch for the sidetone, then paddle revers-

ing for left-handed ops or miswired

paddles. A few bugs were uncovered and

fixed along the way, as I logged more

operating hours with the keyer.

Redefining “Low Power”

Along the way, I got curious about the

current consumption of the chip. I had the

PIC in its low power sleep mode any time

it was not actively doing something like

keying the rig or generating a sidetone.

Although it has now been updated, at the

time, the data sheet for the 12F629 was

pretty sketchy about sleep current. I knew

it would be low, but I needed to determine

whether the CR2032 PC motherboard

clock lithium cell I was using would last

long enough to be practical as I salvaged

the battery from a defective old PC

motherboard I was scrapping. While it was

still reading a healthy 3.1 V, I was plan-

ning to switch to a couple of AAA alka-

line cells if needed. After connecting my

Fluke 77A meter in series with the bat-

tery I was surprised to see it reading 0.00

mA while the chip was idle. Thinking the

meter was simply not accurate at low cur-

rents, I tried my Micronta bench meter on

the 3 µA range. I was quite surprised to

see it read 0.004 µA or 4 nA while sleep-

ing! I abandoned the thought of alkaline

cells—that little lithium battery would last

quite a while! I’ve been using that same

salvaged cell for a few months now, and

it still reads a tad over 3 V when the keyer

is idle.

Figure 1—The completed PicoKeyer in a plastic case. A 1 / 4 inch phone plug is shown

for comparison.

magnetic speaker with a drive require-

ment of only 15 mA. Other piezo or mag-

netic speakers can be used—but be

careful not to exceed the 20 mA current

capacity of the PIC output pin. If you are

building the keyer into a rig, you can sim-

ply inject the sidetone signal into the

radio’s audio stages. A volume control

might be a good idea. If you need more

audio than the PIC can provide directly,

a small audio amp like an LM386 could

be used for more punch. This would of

course require a more robust power

source. The signal produced is a square

wave; some filtering can be used to ap-

proximate a sine wave, if desired.

Q1 is a 2N7000 MOSFET, and is used

to key the radio. You can use a 2N2222A

or a similar NPN transistor with a cur-

rent limiting resistor on the base or emit-

ter. This works, but it requires more

current. Since the MOSFET is a voltage,

rather than current, operated device, it is

ideal for super low power designs such

Construction

I built my keyer on a small piece of

RadioShack perfboard. The few connec-

tions required are pretty simple and

straightforward. Power to the PicoKeyer

chip, U1, is supplied on pin 1, while pin

8 is ground. The photo on the previous

page shows the completed keyer as it ap-

pears before packaging. Figure 1 is a view

of the finished product in a mini plastic

case. Its size relative to a standard 1 / 4 inch

phone plug reveals how small this keyer

really is—and that’s complete with power

supply and speaker! The complete sche-

matic and parts list is shown in Figure 2.

Pin 2 is the sidetone output. If you are

building a standalone keyer you will

probably want a small piezo or low cur-

rent magnetic speaker connected to the

chip through a capacitor. I used a small

Figure 2—The schematic and parts list for the PicoKeyer. The battery is a PC clock

motherboard cell, but any 3 V dc cell can be used.

MN 56701; tel 800-344-4539; www.

digikey.com).

S1—SPST pushbutton, momentary.

SPK—Soberton GT-111PS, Digi-Key

433-1023-ND (see text).

U1—Microchip PIC12F629 with PicoKeyer

code. Available blank from Digi-Key

(part no. PIC12F629-I/P-ND) or

preprogrammed from the author. 2

From December 2003 QST © ARRL

B1—CR2032 lithium battery with holder

or any 3-5 V dc cell (AA or AAA cells

okay).

C1—10 µ F, 6 V electrolytic capacitor.

JP1—Beacon mode switch or jumper

(see text).

Q1—2N7000 MOSFET, Digi-Key

2N7000FS-ND (Digi-Key Corp, 701

Brooks Ave South, Thief River Falls,

as this one. Q1’s gate is connected to pin

3 of the keyer chip, with its source con-

nected to ground. The drain lead is used

to provide positive keying for the radio.

Pin 4 is used to select beacon mode. If

you do not intend to use the beacon fea-

ture, you may simply connect pin 4 to the

positive supply on pin 1. If you wish to be

able to use beacon mode, install an SPDT

switch or a jumper to connect pin 4 to ei-

ther the positive supply or to ground.

The pushbutton switch is connected to

pin 5 of the chip. Since the 12F629 has

internal pull-up resistors, no external re-

sistor is needed to keep the input from

floating.

Pins 6 and 7 are the paddle inputs.

When grounded (or driven low by other

circuits), the keyer will produce a con-

tinuous stream of dits or dahs with proper

spacing. If both inputs are grounded, al-

ternating dits and dahs are sent.

Once all the connections are made,

apply power to the keyer. You should hear

the keyer send 73 in Morse code at 13

WPM via the sidetone only. This indi-

cates that the chip is powered up and

healthy. If you do not hear 73 , recheck

your wiring and reapply power. If every-

thing is okay, you’re all set to start using

the keyer! The default settings are

13 WPM, normal weighting, message

memory empty, Mode B timing and a

beacon delay of five seconds.

If you have experience programming

PIC processors, the HEX code is available

at the ARRL Web site: www.arrl.org/

files/qst-binaries/picokeyer.zip . A pro-

grammed version of the processor with the

latest revisions is available from the

author. 2

button immediately. You may then verify

or change that item. A short press of the

button will exit setup mode, or you may

press and hold the button to keep cycling

through the choices. When you exit the

menu the keyer will end with the Morse

prosign SK .

Menu Selections

The menu selections are as follows:

U (tUne/straight key mode): In this

mode, either paddle input will act as a

straight key. This is useful for sending a

steady carrier for tuning.

S (Speed): Use the paddles to raise or

lower the speed. After each paddle hit the

keyer will send the new setting.

T (Tone): Turns the sidetone output ON

(Y), OFF (N), or sets RIG (R) mode. In

either the ON or OFF settings, the rig is

not keyed when in setup mode. RIG mode

is useful if you wish the transmitter out-

put to be active even in setup mode.

M (Message): Hitting either paddle

will play the current message, followed

by the Morse prosign AR. To record a new

message, hit either paddle again. The

keyer sends K and waits for your input.

Enter the message, making sure to exag-

gerate word spacing. When you’re fin-

ished sending the message, press and

release the pushbutton, and the keyer will

send R to confirm. You may then replay

the message by hitting either paddle. It

may take a couple of tries to get the hang

of the timing, but it’s not too picky un-

less you send the characters too slowly.

W (Weight): Adjusts the weight. Ad-

justment range is from 0 (50% “light”)

to 9 (50% “heavy”), with 5 being the nor-

mal weight setting.

C (Curtis mode): Selects Mode A or

Mode B timing. This determines the be-

havior of the keyer when the paddles are

released after a “squeeze.” In Mode A,

the keyer will complete the element (dit

or dah) currently being sent. In Mode B,

the keyer will “remember” seeing the

other paddle, and will send one last ele-

ment. For example, say you are sending

the letter C. In Mode A, you would not

release the dit paddle until the start of the

last dit. In Mode B you would need to

release both paddles as soon as the sec-

ond dah has started. The keyer will “re-

member” to send the last dit.

P (Paddle): Selects the dit paddle.

Simply hit the paddle you wish to use for

dits. Note that in the menu mode, the

“normal” dit and dah paddle inputs are

used regardless of whether the paddles

have been reversed or not.

B (Beacon delay): Sets the delay be-

tween message transmissions while in

beacon mode, from 0 to 99 seconds.

A (Audio tone): Sets the audio

sidetone frequency. After each paddle hit,

a slightly long dash is sent.

When you are finished altering the

keyer settings, press and release the

pushbutton. The keyer will save all set-

tings to its internal nonvolatile EEPROM

memory and send SK . At that point you

are back in iambic keyer mode, ready to

go!

I have been using this keyer for a few

months now and several other hams have

built them as well. One of the things I

like is the ability to change features very

quickly; it took about an hour of revising

the program code to make a version pin

compatible with the popular RockMite

transceiver. 3 Another couple of hours and

I had a version that used a potentiometer

to set the speed instead of the menu; it

was even less time to produce one to re-

place another 8-pin keyer chip that used

a different pinout. While I still enjoy sol-

dering, I also like this facet of our won-

derfully diverse hobby. Besides, I can

write code while in an airline seat—an

environment in which a soldering iron is

somewhat impractical!

Notes

1 www.microchip.com .

2 A pre-programmed version of the 12F629 PIC

processor with the author’s latest HEX code

is available from the author for $8.95

( www.hamgadgets.com ).

3 D. Benson, K1SWL, “The RockMite—A

Simple Transceiver for 40 or 20 Meters,”

QST, Apr 2003, pp 35-38.

Operation

Operating the PicoKeyer is simple and

straightforward. To use it as a normal

iambic keyer, simply apply power and

connect the paddles. Dual or single lever

paddles can be used. To send the contents

of the message memory, press and

quickly release the pushbutton once.

While the message is being sent, any

paddle or pushbutton input will immedi-

ately end the transmission.

To enter setup mode, press and hold

the pushbutton. The keyer will step

through the setup menu choices, with

about a one second delay in between.

When you hear the character for the item

you want to check or change, release the

Photos by the author.

Dale Botkin\, NØXAS, was first licensed in

1981 as KA5MSS, although that call and

HL9CA both lapsed without ever having been

used. Dale was relicensed as a Technician in

1994, with subsequent upgrades to General

and Amateur Extra. He enjoys casual opera-

tion using low power CW and PSK31 on the

HF bands. He also operates VHF and UHF

mobile and makes an occasional FM satel-

lite contact. As is obvious, Dale is an avid

radio experimenter, especially with embed-

ded microcontrollers. You can contact him at

16624 Elm St, Omaha, NE 68130 or at

n0xas@arrl.net .

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