Look at my Wave Generator, or "Garage Tek Introduces..."

Regurgitating last weeks question in more convenient form,

I wanted to get some opinions on the appearance of this wave generator I made, and maybe some comments.

The basic specs are;

50 ohms output impedance (changes somewhat with increasing frequency) 1MHz in 6 ranges coarse freq control fine freq control 9 volt battery compartment (no ext. DC) level control 0 to 5 volts dc no offset control, inherent offset 2mV typical max 250 mA ouput current capacity (400mA peak) 10 mA nominal current draw for light loads BNC output Banana-Lug outputs LED power light (yellow). Dims when unable to sustain 5 volts internal regulation.

Dubious aspects are limited to square wave output only, which becomes a trangular wave at 500 kHz due to slew limiting.... and the lettering is a funky but decent looking labelling tape.

Future mods will include getting rid of the odd knob, so all 4 knobs will be the same

Please have a look at it and tell me what you think some well-funded person would pay for it if they actually wanted one... and comment on how you'd change the appearance please.

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I do plan on selling these.

Thanks!

Geoff

Reply to
engineer
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Um, how do you plan on 5V driving 250mA into 50 ohms? If you can do this, I'll buy one. Just to be part of the revolution, you see. The revolution in physics and the imminent collapse of the universe.

Reply to
a7yvm109gf5d1

It's a pretty case. The frequency range should be labelled properly. Any photo's of the inside?

Ken

Reply to
Ken Taylor

I didn't make the claim that it could defy physics.. but the output can tolerate 250mA continuously, 400mA peak.

Maybe you'd be interested in my Universe Support Sticks? A copy of Ohm's Law perhaps?

Reply to
engineer

The silly range numbers 1,2,3,4,5,6 are right beneath 1Hz, 10Hz,

100Hz, 1kHz, 10kHz 100kHz..each denoting the lower end of those ranges There are photos of the inside of the prototype, but i havent coated the boards yet on the first batch of four.. and maybe I my well-made circuits like their privacy;)
Reply to
engineer

Drive 250ma into a coil, swith the coil for the pulse duration to 50 ohms,for short pulses:done!!

Reply to
Sjouke Burry

This coil is supplied with the device? How come all the function generators since the last six or so decades don't have this feature?

Reply to
a7yvm109gf5d1

How can a 9V battery supply 250mA to a 50 ohm load? If your output impedance is determined by the output impedance of your transistors, common design practice is to "make up" the rest with resistors. So if you short the output, you get 9V across ~50 ohms. My copy of Ohm's Law gives me 100mA in a SHORT CIRCUIT condition. IN DC. The RMS value for a

50% square wave would be 50mA. But you knew that, right? Are you selling negative resistors to go along with this device? Or a new Big Bang? What does "tolerate" mean? If you chose transistors with 400mA collector current, it is dishonest to market your "device" as being capable of " 250 mA ouput current capacity" if you can only ever supply 100mA with the supplied battery. If you use 100A transistors, would you claim 100A output current capacity as well? Or maybe you meant I can shove 400mA "peak" (how long?) with my macho power supply into the output and it won't matter? Here's a question: Do you even know why generators have a 50 ohm output impedance?
Reply to
a7yvm109gf5d1

A good alkaline 9 volt will deliver at least 450 mA when the generator is driving a short circuit.

I didn;t intend to write the feature list with any hand-holding features.. just that facts and you can sort out what the deal must be, I make no claims to magic.

The currents I've measured were by fancy schmancy scope across reistors of known and tested value.

I don't know the history of the 50ohm standard, and I know plenty so work on someone else buster.

Reply to
engineer

So your "fancy schmancy scope across reistors of known and tested value" showed that you can magically get 250mA thru 50 ohms from a 9V battery ?:-)

...Jim Thompson

--
|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
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Reply to
Jim Thompson

In case anyone doesn't know ohms law and could'nt figure out what I said in English,

I never, ever, made or inferred any claim of driving 450 mA in 50 ohms.. god, you people are helpless, thank god I won't work for you.

Exact measurements;

450 mA into a short,

3.12 volts = 0.312 Amperes at 1 kHz into 1 ohm

2.04 volts into 10 ohms @ 1 kHz =.204 Amperes (x 2.04 volts= .416 watts )

4.0 volts into 51 ohms @ 1 kHz = .0784 Amperes -> .313 watts

4.48 volts into 100 ohms @ 1 kHz = .0448 Amperes 0.2 watts

The bloody output is nominal 50 ohms, about 40 internal and 10 on the outside, from the chips perspective it's an ideal device driving through a 10 ohm resistor. The ouput impedance varies up to 1 MHz and passes through 50 somewhere on the 100ks, impedance doesnt make a hell of a difference unless driving a coaxs, but if you were smart then maybe I'd work for jerks like you, but your NOT so I WONT.

Reply to
engineer

Appearance is good.

-- You should add a duty cycle, or mark vs. space time control.

Since you've got a stable 9V supply, you could also use an output buffer to push it to 8-9V output. If you intend on using this for digital circuits, then simply fixed 5V would be fine, too.

Is that an amplifier spec, or the "low" voltage?

As mentioned, 5V through 50 ohms isn't exactly 250mA...

Why? Is battery internal resistance limiting, or is it the regulator? It seems to me a circuit should not be produced that can be fiddled with through the output! ;)

You should build a buffer stage with 2N4401's and -03's, or at least get a fast, moderately high current, rail-to-rail buffer (op-amp, or something digital).

Humm no more than $50 I think. (Not that I care, I have my own 20MHz benchtop function generator. :)

Kits might be a good idea.

Tim

-- Deep Fryer: a very philosophical monk. Website:

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Reply to
Tim Williams

Did ANY of you heroes notice I asked a friggen question ? Hell no, you were too busy being internet assholes.

Reply to
engineer

[snip]

Clearly. Plonk!

...Jim Thompson

--
|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
 Click to see the full signature
Reply to
Jim Thompson

why does an led dim on a sagging regulator due to inablity of the dying battery to feed the regulator to that level...

the answer is that 5 minus 2.2 is 2.8 .. when the regulator output sags to 4 volts because the battery has dropped to 5, etc, it boecomes

4-2.2=1.8

2.8 and 1.8 across the same resitor suggests two rather unique currents.

It costs $35 in parts, and I make the boards... kit's are a good idea, but kit's aren't as close the right category for me to do that... and there are oodles of kits out there (and not so many surface mount) and where is the money, in selling a classroom's qty at $400 net or a kit at $4 net... this isnt a serious business, its fodder for a line that supports serious business.

Ok, enough of that.. let's let the jerks get back to making noise

Reply to
engineer

Well clearly, if it can supply 400mA short circuit, it simply isn't 50 ohms! Everything connecting to 50 ohm line is supposed to have a 50 ohm input or output impedance.

Consider you have this connected to a long length of coax, and a pulse (from elsewhere, or from the device itself via a reflection from another mismatch) reaches the output terminal. The wave will be superimposed on whatever the output is, so we don't care about output state, only output resistance. (Note that, if output impedance varies with state, which it can depending on what you've used, we WILL care about state.) If the output is 400mA short circuit and 5V open circuit, that's an impedance of 12 ohms. This will reflect a pulse about -3/4 amplitude (that is, somewhat attenuated, and going the opposite polarity), making for a real ugly signal on the line and causing glitches with the driven input(s).

A triangle wave at 500kHz is a 1µs rise or fall time, out of 5V is all of

5V/µs slew rate. That's pretty pokey. Nonetheless, you will observe transmission line effects in cables over 10' long, and especially in longer lengths.

Well, I honestly don't know why you put a BNC on the damn thing then. LOL

CAT5, twin lead, extension cord, well absolutely any transmission media, has a characteristic impedance that must be matched for clean operation at high frequency. It is utterly inescapable and you are at best daft to ignore it when working with anything over a megahertz!

Tim

-- Deep Fryer: a very philosophical monk. Website:

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Reply to
Tim Williams

Oh, well then you could've said internal resistance (battery voltage sag). Fair enough.

Now limit the output so it doesn't do it ;o)

Tim

-- Deep Fryer: a very philosophical monk. Website:

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Reply to
Tim Williams

The approach was to make a tool that that was good in its ability to do what it does while staying simple enough to keep costs in the low range for anyone who wants to spend less than $300 (Here comes Thompson's claim I want $299..) for that level of functionality.

Every once and a while I have to fiddle with the internet only to be reminded what kind of assholes americans usually are...like Thompson.

Reply to
engineer

Well first you said you had a 50 ohm output impedance. Now you are saying you in fact have a much lower output impedance, but usually drive 50 ohm loads with it. That's okay for many applications, it just won't behave like a 50 ohm output impedance would.

If you actually had a 50 ohm output impedance, the current through a shorted output jack would be twice that through a 50 ohm load resistor (ie, 50 inside plus 50 outside = 100 ohms). And you would need a much, much higher internal voltage to get 450 ma through that short and the internal impedance, unless you have some sort of clever active impedance doodad in your box.

Reply to
cs_posting

The BNC is on because the ouput spectrum goes up to . oh forget it, you people are tedious

I'll be taking the web page down

and trying to avoid further ineraction with the cosat-to-coast asshole contest so visible on the net

Reply to
engineer

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