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It's called a trimming potentiometer, and you've got at least two of them. Changing one changes the frequency of the oscillator, and the phase shift across the other two stages.

You should try it. You don't have to shepherd many products through production to work out that interacting adjustments aren't a good idea.

-- Bill Sloman, Nijmegen

What is your screen size? Web designers need to be aware that not everyone has a large monitor. There are simple javascripts to direct visitors to alternate web pages for low resolution monitors.

On a sunny day (Mon, 8 Nov 2010 09:00:27 -0800 (PST)) it happened Bill Sloman wrote in :

I hope you can see that if you drive into an inductor with those 2560 steps / second, that the current smoothes out nicely between steps. di = dt/L.

Price of a resistor is? Obtainability from Maxim is?

So, why did you stop?

proud on

hardware part of their chips.

before the PIC

IIRC some PICs allow or have a dual speed oscillator. Have not used the feature yet, but precisely for this kind of thing. Still have not looked up the data sheet no?

DDS, so how much does you DDS use?

You are evading the question, how much current does your DDS chip use?

Maybe you should just say you are wrong, apologise to those you have insulted, and be done with it. It would be a plus point for you.

On a sunny day (Mon, 8 Nov 2010 09:15:49 -0800 (PST)) it happened Bill Sloman wrote in :

Sloman falling back into old warming mantra ..

I didn't see that one - sounds even simpler.

I think my way can be done without any "tuning" and can also be driven by a crystal-derived oscillator if needed.

But I haven't really thought it all through.

I can appreciate your efforts there, but I hope you also teach them that the likelihood the people they end up working with in industry will be using the term "rheostat" is rather low. :-)

I was in one of the series of analog design classes where some student pointed out to the professor that his symbol/name for Vgs-Vth of a MOSFET was different than what the professor the prior quarter had used. His response was, "everywhere you work, there'll be a different symbol or name used for Vgs-Vth... you might as well get used to it now!"

For variable resistors, everywhere I've worked it's actually always just been "trimpot" regardless of how it's hooked up.

More memorable professor quotes... some kid in a microwaves lab pointing to a pair of coax cables... "So I just hook those wires together?" Professor (with Indian accent): "In my class you will not call those wires; those are transmission lines!" :-)

---Joel

Since the goal was 40 hours' operation from 4xAA cells, low power is not the overriding concern. A typical AA cell, such as the Energizer E91, can easily supply 50mA for 40 hours.

More likely: the uC would draw 5mA or less, for a total draw under

Yes, agreed. I still prefer the digital approaches--cheaper, lower parts count, greater accuracy, no adjustments, and more repeatable in production. IOW, less hassle.

-- Cheers, James Arthur

You hook the rheostat up to the condenser, and connect that to the grid of the...

Spread-spectrum. It was an example of an analog, RF, digital, software, plus micropower design I did 23 years ago, more complicated and demanding than the current requirement. As for expertise, I'm not going to argue with you over who's more expert than who.

I don't understand your concern. If the entire uC switching at 16MHz draws 11mA (80c51 family), why are you worried about three outputs switching at 20KHz? Even at 1MHz switch rate, f*c*v^2/2 ~=3D 125uW/ output. That's nothing.

You're worrying about things that don't matter.

-- Cheers, James Arthur

On Mon, 8 Nov 2010 09:18:25 -0800 (PST), "Ken S. Tucker" wrote:

--- I'm confused.

Th OP was Mark Weaver, who asked for the device, but the 120° shift-register shifter was mine, not his.

In any case, there was an error in the shifter, which was putting out pulses separated by 60°, not 120°.

Here's the fix:

TRIM FOR 60Hz / +-[POT]-[Rt]-+ | | | +-------+ | +--------+ +-|TH OUT|--+--|> 1D|---+ | |__ | | | | +-|TR | +--|1Q | | | |_ | | | | | Vcc--|-|R | +--|2D | O | +-------+ | | / \ | 7555 +--|2Q | /___\ [Ct] | | | | | +--|3D | | GND | 5Q|---|---->240° +--|3Q | | | | 3Q|---+---->120° +--|4D | | 1Q|-------->0° +--|4Q | | | | +--|5D | | | Vcc--+-----------|6D | | |_ | +--[R]--+--O|R | | +--------+- | HC174 [C] | GND

The LTspice circuit list is at the end of this post and it shows it running with a battery supply (+3V and -3V) and a 2 pole Sallen-Key lowpass on each phase cleaning up the three square waves nicely and, with the dual supply, making _real_ AC!

Nominal current for everything but the clock oscillator is less than

His coil load is going to be about 333 ohms so, with nearly 6VPP available to drive them, (if he uses that much) they'll draw about

Add to that the oscillator, and the total drain from the battery will be around 7mA.

A good alkaline AA cell can supply 10mA for about 300 hours until its output voltage falls to 1V,:

So it looks like this rig out to be able to give him over 7 times the battery life he was looking for.

Somewhat less, because I haven't considered what it takes to run the coil drivers, (having not put any in yet,) but certainly less than a mA apice, I'd think.

Any suggestions?

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SYMATTR Value 2.25e-8 SYMBOL res -624 80 R90 WINDOW 0 65 62 VBottom 0 WINDOW 3 70 60 VTop 0 SYMATTR InstName R2 SYMATTR Value 1e6 SYMBOL res -480 80 R90 WINDOW 0 -30 53 VBottom 0 WINDOW 3 -28 56 VTop 0 SYMATTR InstName R3 SYMATTR Value 1e6 SYMBOL Opamps\\LT6004 -432 80 R0 SYMATTR InstName U1 SYMBOL cap -496 752 R0 WINDOW 0 -41 34 Left 0 WINDOW 3 -88 65 Left 0 SYMATTR InstName C4 SYMATTR Value 1.13e-8 SYMBOL cap -624 640 R0 WINDOW 0 -55 -2 Left 0 WINDOW 3 -87 35 Left 0 SYMATTR InstName C5 SYMATTR Value 2.25e-8 SYMBOL res -624 720 R90 WINDOW 0 65 62 VBottom 0 WINDOW 3 70 60 VTop 0 SYMATTR InstName R4 SYMATTR Value 1e6 SYMBOL res -480 720 R90 WINDOW 0 -30 53 VBottom 0 WINDOW 3 -28 56 VTop 0 SYMATTR InstName R5 SYMATTR Value 1e6 SYMBOL Opamps\\LT6004 -432 720 R0 SYMATTR InstName U3 TEXT -2352 560 Left 0 !.tran 1 startup uic TEXT -2352 592 Left 0 !;ac oct 128 1 100 TEXT -288 720 Left 0 ;>PHASE 1 TEXT -288 400 Left 0 ;>PHASE 2 TEXT -288 80 Left 0 ;>PHASE 3

--- JF

Right. Even if your newsreader is dumb as a stump, the poster should be smart enough to trim the quote before replying.

ll

nd.

I prefer names that refer back to hardware I can buy.

Which you can't be bothered to specifiy.

Any good product won't need any adjustment at all.

-- Bill Sloman, Nijmegen

"Rheostat" is a quite common term, even now. Digital pots will show "rheostat connections" and some are only "digital rheostats".

That's the great thing about standards; there are *so* many to choose from.

The part is usually called a "pot" if it has three connections, no matter how many are used. Its *usage* will often (correctly) be called a "rheostat" (or "variable resistor" ;-).

Or in power lab, "Oh, Shh....".

If Slowman were worrying about things that didn't matter, he would be very worried about himself!

Have for at least 20 years. Slowman is simply clueless.

insist

without

The ADuM3470 certainly gets up to 24V (regulated) and they show 30V (+/-15V) applications.

I hate people calling me just because I was browsing for parts. If I need help I'll *ask*. I hate stores where the sales people hover.

eal

=A0I

What you seem to miss is that in order to know when to switch (at a

I'm worrying about things that certainly used to matter, and I note that it was Jan Pantelje - not you - who first produced a concrete example of a microprocessor that could produce good PWM in Mark Weaver's application without drawing excessive amounts of current. Your 80C51 doesn't seem to be the NXP part

since your 11mA is higher than the typical current drawn at 16MHz for the NXP part, if lower than the worst case (see figure 21) so one might wonder which actual part (if any) you had in mind.

-- Bill Sloman, Nijmegen

an

You and Rich Grise don't understand any of the phsyics, so you feel free to confuse anthropogenic global warming - which is a well-founded scientific hypothesis - with some kind of revealed religion.

It's an argument from abject ignorance, but - precisely because you are depressingly ignorant - you don't realise quite how stupid it makes you look.

-- Bill Sloman, Nijmegen

On a sunny day (Mon, 8 Nov 2010 15:42:29 -0800 (PST)) it happened Bill Sloman wrote in :

Nobody understands 'phsyics'.

Well, the warmist "religion" is well known. A couple of entrepreneurs trying to sell windmills and useless photo voltaics. They do this by appealing to fear (for warming, if tha does not happen to happen to cooling, and human compassion for melting polar bears etc.

The ones who actually install the solar panels on their roof in the Netherlands are not so much stupid looking, but just plain stupid, and you and your climate jive friends are the ones misguiding them. Do you actually have your own solar panels, or windmill, on the roof, over there? If not nothing but words. If you were really as intelligent as you think you are then you would have come up with a new form of energy long time ago, after all a PhD in chemistry and electronics should turn up something useful.