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Author Topic: How to build a cw practice key..  (Read 4968 times)

Posts: 56

« on: February 21, 2007, 05:57:14 AM »

I want something i can set on the couch or wherever and do my practice. One i can here , but not real loud.. I have built one (( BY ACCIDENT)) probabily 4 years ago or so , but have  no idea how to go about it now.I remember i had a buzzer , battery , and button. I built them out of scrap parts i had. Any ideas let me know..

                                    Roy & Mary

Posts: 8911


« Reply #1 on: February 21, 2007, 06:09:33 AM »

Lots of options if you search google :

cw practice oscillator

Most of them use parts that might still be available at Radio Shack.



Monkey/silicon cyborg, beeping at rocks since 1995.

Posts: 104

« Reply #2 on: February 21, 2007, 12:40:59 PM »

A practice oscillator that I plan to prototype soon (as something for some local cub scouts (ages 7-8) to "build" inexpensively, if it works) is:

- two short lengths of wire, each soldered to an unpainted steel thumbtack (this is the limit of the prep work I'll do for the cub scouts)

- those thumbtacks are pressed into opposite sides of the squeeze-side of a wood clothes pin (the clothes pin is the one part I'm still missing for the prototype) - place them so that when the clothes pin is squeezed, the thumbtacks contact each other (with care, you might be able to place them so that they have a very narrow gap when relaxed)

- one of the wires connects to one lead of a piezo-buzzer (Radio Shack has two that buzz in the 100's of Hz instead of the 1000's of Hz; one of these can operate on 1.5V) - for the kids, this can be a simple twist-connection with a little electrical tape

- the other wire and the other buzzer lead are placed on opposite terminals of a AA battery and held in place with a rubber band

Total price: $3.29 plus tax for each buzzer, plus a pack of thumbtacks, a bag of clothes pins, a bag of rubber bands, and a few packs of el-cheapo AA batteries (the buzzers draw 15mA - at this rate, the battery isn't going to drain anytime soon).  I wouldn't be surprised if you have all those parts (except the buzzer) already around the house to build one of these.

It might need a current-limiting resister to protect the buzzer.  It might not even work (this is why I plan to prototype it before suggesting it to the den leader).  A variation would be to forget about the clothes pin and thumbtacks, and connect the buzzer & battery to a telegraph key if you already have one (or if you feel like building the $5 key that was in QST a few months back).

Take care,

Posts: 17476

« Reply #3 on: February 21, 2007, 10:11:34 PM »

There are two items of equipment that you are talking about.  One is
the key itself - a switch designed to be opearted quickly by hand, and
the other is a code practice oscillator that makes an audio tone when
two wires are connected together (usually by the key, but you can use
it for other purposes as well.)

For the key itself you need some means of closing a circuit with a
spring return.  A momentary push-button will work but won't go very
fast.  Probably the simplest one is to use a teaspoon from the thrift
shop:  find a thin sheet of wood or plastic for the base and mount a
larger block of such material on top of it - the exact dimensions will
depend on the spoon that you get (it has to be metal, of course.)
Attach the spoon handle to the top of the block with the bowl of the
spoon hanging off the side of it.  Using two screws through a metal
bar across the handle is best, as it allows the bowl to be moved closer
or further from the block to adjust the tension.  Then put a screw into
the base right under the bowl of the spoon so when you press down
on the bowl it contacts the screw.  Attach one wire to the spoon handle
and the other to the screw, so that pressing on the spoon completes
the circuit.  This will take some adjustment - you want a fairly small
gap so you don't have to press the spoon down too far to make contact,
and enough tension to spring the spoon back away from the contact
when you let up on it but without being too hard to press.  Adjust the
tension by pulling the bowl out further from the support block so
more of the handle extends past it, and adjust the throw either by moving
the contact screw  up and down or bending the spoon handle a bit.  The
exact settings are a matter of personal preference.

The "noise maker" part can be a simple buzzer and battery or at two
transistor circuit connected to a speaker.  Here is one using a NE555
timer IC:

Here is one using discrete transistors:  you can use 2N2222 or 2N3904
transistors (or just about any NPN type) and put a speaker or headphone
in the collector lead of one of the transistors (in place of one of the
resistors marked R3.)

Posts: 16

« Reply #4 on: February 24, 2007, 04:23:35 PM »

If you have some paddles, I suggest the pico keyer. It costs about $20 shipped. It is very simple and when you are done, you will have a programmable keyer for your rig.

I believe there is a review on eham too.
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