F Knobs vs F Buttons on Signal Generators

My old Marconi 2019A units have up/down buttons, as well as the keypad.

Leon

For development work, buttons (like surface mount components), are a grade #1 PITA. Human friendly alternatives make use of the expensive and lost art of mechanical engineering. I like the spin wheel on my Racal synth. Must be 2Ibs of metal in the flywheel. Best for me is a sig gen based on a magnificently engineered, anti-backlash geared, ball-raced, 2 gang air spaced capacitor, assembled with a high kilopoise lubricant. Seems to have near infinite setability and ineffable smoothness.

Gee... I just got an idea what it takes for a good frequency control knob. No wonder the signal generator designers make units with only control buttons. It's cheaper and simpler than a knob. :P

D from BC

Most of the time you have a laptop or PC at hand and then you can use a mouse and a keyboard for frequency changes, like I've implemented in

.

But I have a very nice optoelectronic encoder here (

), which I plan to integrate, too, which will be read from the software. Then you can focus the value you want to change with the mouse (e.g. frequency or duty cycle) and adjust the value with the knob.

--
Frank Buss, fb@frank-buss.de
http://www.frank-buss.de, http://www.it4-systems.de

If you don't want to roll this all yourself, you might use a Griggin Powermate:

. It's quite popular with the GnuRadio and FlexRadio guys as a tuning knob...

---Joel

Now that's a knob. Great industrial look. Arrff! Arfff! :)

Those little plastic nipple knobs like on those cheapo 2Mhz function generators are the worst.

D from BC

Two of the buttons are up/down. On the particular model I have, you can set the cursor to a digit, and it runs that digit up/down (and the ones to the left if you keep going). Along with a wide array of sweep options, it works for me.

You could do lots of nice stuff with a rotary encoder and speed sensitivity (change faster as it's spun faster - change slower as it's turned slowly). Follow the lead of snooty stereos and make the knob from solid metal for nice heft. Put a GPIB interface on it and you can plug it into mine ;-)

As for generators where the knob IS the frequency setting, and you have to fiddle with where the knob is (within a 270 degree arc, hard-mapped to output) to get a specific frequency, yuck.

--
Cats, coffee, chocolate...vices to live by

On a sunny day (Fri, 04 Jan 2008 12:51:12 -0800) it happened D from BC wrote in :

I have a transmitter with both a dial and push buttons to set either Hz, 10Hz,

100Hz etc. Both are very useful. Problem with the dial is that it sometimes skips steps, so you really have to look at the display (the dial clicks, but the clicks are not reliable steps). The dial is nice for playing around, checking.

If you look at the prices of encoders there's the class that goes up to about 36 counts per turn (~$5, typically mechanical) and the class that goes up to hundreds (~$50, typically optical). The low-count ones are terrible for inputs that require both high precision and large gross movements (like frequency).

The best homebrew compromise to buying an expensive optical encoder is to tear up an old mouse and use one of its optical encoders. I think there are also high-res encoders in VCR heads, which come with nice metal "knobs". ;-)

--
Ben Jackson AD7GD

http://www.ben.com/

Can you use music-style control knobs and get them to control your GPIB/USB chain? I use a Nostromo game pad with its software to control my CAD programs.

Thanks! I saw one once and forgot the name! SWEET!

Like this?

Cool... I didn't know that existed..

I think I found my new toy. :)

D from BC

On a sunny day (Fri, 04 Jan 2008 18:19:50 -0600) it happened Ben Jackson wrote in : I think

I am not aware of that, would be nice though. There is a one revolution tach, and position info is obtained from the head signals. Some old Philips helical scan cassete players used piezo actuators to correct head position. The mass of the head drum is so big (your big knob) that you cannot change its speed a lot in one revolution.

I've made some rotary knobs using an hp 200 pulse rotary encoder, a

1/4-inch thick x 2-inch diameter piece of aluminum on the shaft for inertia and some (switchable) external logic to divide down the pulses for fine tuning. The large disk gives it a nice feel. It turns smoothly and I can give it a strong twist to rapidly get the display to near where I want it to be. al

Since you mentioned GnuRadio, I find it interesting that Griffin specifies compatibility with XP & OS X

--but nothing Open Source.

Yeah, sad but not too surprising...

If I had to guess, I would say that Griffin powermate is probably just a USB HID-type device, so it's likely very easy (for someone familiar with USB HID devices under Linux) to get it working... it might even "just work" right out of the box.

I have one of those cool little Apple aluminum Bluetooth keyboards and I've only ever used it with Windows and Linux boxes -- it's never "spoken" to a Real Apple computer yet, even though it's only advertised as being compatible with them.

Interface standards are a good thing...

I wouldn't even touch a frequency generator that hasn't a rotary knob to set the frequency.

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Reply to nico@nctdevpuntnl (punt=.)
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That expensive? I'm quite sure they can be found much cheaper. 36 counts per turn is fine. Software can determine the actual number of steps depending on the speed.

For hobby purposes, one can also use an old stepper engine from a 5

1/4" floppy drive.

--
Reply to nico@nctdevpuntnl (punt=.)
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Do you mean using the entire stepper motor? One detects and decodes the pulses from the drive coils?

D from BC