Need a little design help on my latest project
in [Design]
|
Prev: Magnetism is really -- WHAT?
Next: low-end scope
From: Charlie E. on 3 Mar 2010 12:58 On Wed, 03 Mar 2010 09:43:27 -0800, Joerg <invalid(a)invalid.invalid> wrote: >Charlie E. wrote: >> On Tue, 02 Mar 2010 13:12:46 -0800, Joerg <invalid(a)invalid.invalid> >> wrote: >> Naw, by April the weather will be perfect here and in Phoenix. I >> actually went swimming a week ago, and should be able to again next >> week! Just need a few days in a row of 76+ highs... >> > >Are you in Florida? A client near Palm Beach told me that they regularly >dive into the pool now. Wish I lived there ... No, I am down in Desert Hot Springs, just across the valley from Palm Springs. I only have a solar heater on my above ground pool, so I need temps to be in the upper 70's to low 80s to reall be able to swim comfortably. By July, the pool temps will be in the 90s, even with 'cooling!' Charlie
From: Jim Thompson on 3 Mar 2010 13:12 On Wed, 03 Mar 2010 09:58:40 -0800, Charlie E. <edmondson(a)ieee.org> wrote: >On Wed, 03 Mar 2010 09:43:27 -0800, Joerg <invalid(a)invalid.invalid> >wrote: > >>Charlie E. wrote: >>> On Tue, 02 Mar 2010 13:12:46 -0800, Joerg <invalid(a)invalid.invalid> >>> wrote: > >>> Naw, by April the weather will be perfect here and in Phoenix. I >>> actually went swimming a week ago, and should be able to again next >>> week! Just need a few days in a row of 76+ highs... >>> >> >>Are you in Florida? A client near Palm Beach told me that they regularly >>dive into the pool now. Wish I lived there ... > >No, I am down in Desert Hot Springs, just across the valley from Palm >Springs. I only have a solar heater on my above ground pool, so I >need temps to be in the upper 70's to low 80s to reall be able to >swim comfortably. By July, the pool temps will be in the 90s, even >with 'cooling!' > >Charlie Same here. The solar only seems to buy me about a month on each end of the "season" :-( I like the pool to be 80�F+ (I have a heat pump for the spa :-) ...Jim Thompson -- | James E.Thompson, CTO | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | I love to cook with wine. Sometimes I even put it in the food.
From: Charlie E. on 3 Mar 2010 13:25 On Wed, 03 Mar 2010 10:57:41 -0700, Jim Thompson <To-Email-Use-The-Envelope-Icon(a)My-Web-Site.com> wrote: >On Wed, 03 Mar 2010 09:43:27 -0800, Joerg <invalid(a)invalid.invalid> >wrote: > >>Charlie E. wrote: >>> On Tue, 02 Mar 2010 13:12:46 -0800, Joerg <invalid(a)invalid.invalid> >>> wrote: >>> >[snip] >>>>> >>>> I think Jim needs to order some more global warming before people will >>>> come, or everyone has to bring jackets :-) >>> >>> Actually, the FETs you suggested have spice models on their sites that >>> worked like a charm. Order some complementary pairs this afternoon, >>> some in DIP8 and some in SOT23 form factors. I will crank them up on >>> friday and see how things perform! >>> >>> Naw, by April the weather will be perfect here and in Phoenix. I >>> actually went swimming a week ago, and should be able to again next >>> week! Just need a few days in a row of 76+ highs... >>> >> >>Are you in Florida? A client near Palm Beach told me that they regularly >>dive into the pool now. Wish I lived there ... > >Charlie is near Palm Springs, Californica. > >Virtually the same kind of climate as around here... hot enough to >keep the riff-raff away ;-) > > ...Jim Thompson Yeah, there is still a pretty big distinction between 'locals' and 'snowbirds.' We do have a lot of residents that are here only for part of the year, say from October to April. During that part of the year, traffic is worse, the crowds are worse, but it is also when business thrives. And now that Palm Springs is once again encouraging tourism, after all the spring break madness of the past has calmed down, means we are getting more visitors. Our own town has lots of little spas, some fancy, some basic, that all boast our hot mineral water. We are also getting into the 'vortex' business, as we have high winds (Air), the San Andreas (earth), our mineral water (Water) and of course, high temperatures (both in the air, and in our water for Fire!) So, Welcome to Desert Hot Springs! Now go home! ;-) Charlie
From: Jim Thompson on 3 Mar 2010 16:06 On Wed, 03 Mar 2010 10:25:25 -0800, Charlie E. <edmondson(a)ieee.org> wrote: >On Wed, 03 Mar 2010 10:57:41 -0700, Jim Thompson ><To-Email-Use-The-Envelope-Icon(a)My-Web-Site.com> wrote: > >>On Wed, 03 Mar 2010 09:43:27 -0800, Joerg <invalid(a)invalid.invalid> >>wrote: >> >>>Charlie E. wrote: >>>> On Tue, 02 Mar 2010 13:12:46 -0800, Joerg <invalid(a)invalid.invalid> >>>> wrote: >>>> >>[snip] >>>>>> >>>>> I think Jim needs to order some more global warming before people will >>>>> come, or everyone has to bring jackets :-) >>>> >>>> Actually, the FETs you suggested have spice models on their sites that >>>> worked like a charm. Order some complementary pairs this afternoon, >>>> some in DIP8 and some in SOT23 form factors. I will crank them up on >>>> friday and see how things perform! >>>> >>>> Naw, by April the weather will be perfect here and in Phoenix. I >>>> actually went swimming a week ago, and should be able to again next >>>> week! Just need a few days in a row of 76+ highs... >>>> >>> >>>Are you in Florida? A client near Palm Beach told me that they regularly >>>dive into the pool now. Wish I lived there ... >> >>Charlie is near Palm Springs, Californica. >> >>Virtually the same kind of climate as around here... hot enough to >>keep the riff-raff away ;-) >> >> ...Jim Thompson > >Yeah, there is still a pretty big distinction between 'locals' and >'snowbirds.' We do have a lot of residents that are here only for >part of the year, say from October to April. During that part of the >year, traffic is worse, the crowds are worse, but it is also when >business thrives. And now that Palm Springs is once again encouraging >tourism, after all the spring break madness of the past has calmed >down, means we are getting more visitors. > >Our own town has lots of little spas, some fancy, some basic, that all >boast our hot mineral water. We are also getting into the 'vortex' >business, as we have high winds (Air), the San Andreas (earth), our >mineral water (Water) and of course, high temperatures (both in the >air, and in our water for Fire!) So, Welcome to Desert Hot Springs! >Now go home! > ;-) > >Charlie Someone actually planted a billboard at the NM-AZ border (on I40) saying exactly that... and it took AZ over a year to force it to be taken down :-) ...Jim Thompson -- | James E.Thompson, CTO | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | The only thing bipartisan in this country is hypocrisy
From: dagmargoodboat on 3 Mar 2010 18:21
On Mar 2, 10:11 pm, George Herold <ggher...(a)gmail.com> wrote: > On Mar 2, 9:10 pm, dagmargoodb...(a)yahoo.com wrote: > > > > > On Mar 2, 1:48 pm, Joerg <inva...(a)invalid.invalid> wrote: > > > > Charlie E. wrote: > > > > On Mon, 01 Mar 2010 17:35:29 -0800, Joerg <inva...(a)invalid.invalid> > > > > wrote: > > > > >> Charlie E. wrote: > > > >>> On Mon, 01 Mar 2010 14:30:26 -0800, Joerg <inva...(a)invalid.invalid> > > > >>> wrote: > > > > >>>> langw...(a)fonz.dk wrote: > > > >>>>> On 1 Mar., 20:12, Joerg <inva...(a)invalid.invalid> wrote: > > > >>>>>> Charlie E. wrote: > > > >>>>>>> On Mon, 01 Mar 2010 10:38:45 -0800, Joerg <inva...(a)invalid.invalid> > > > >>>>>>> wrote: > > > >>>>>>>> Charlie E. wrote: > > > >>>>>>> <snip original problem...> > > > >>>>>>>>> Joerg, > > > >>>>>>>>> Thanks for the advice. Yes, I had been concentrating so hard on the > > > >>>>>>>>> amplifiers I never really considered the LEDs. In my mind, they would > > > >>>>>>>>> just 'work' and I could then adjust accordingly. Didn't realize that > > > >>>>>>>>> they would vary that much. Will have to look at maybe adding a higher > > > >>>>>>>>> voltage, and go with the constant current drives for them. This does > > > >>>>>>>>> need to be pretty accurate! > > > >>>>>>>> Where is your VCC coming from? Regulator? If so, what's the minimum > > > >>>>>>>> voltage going into that regulator? If it is a battery that won't drop > > > >>>>>>>> below about 4.5V and has low load ripple (low source resistance, added > > > >>>>>>>> capacitors) fixing this part of the circuit would become fairly simple. > > > >>>>>>> Hi Joerge, > > > >>>>>>> I only have two AA batteries, so voltage is only about 2.5-3.1 volts. > > > >>>>>>> That was why I added in the power supply, to try and stabilize that > > > >>>>>>> voltage. Most of the parts were pretty power tolerant, but I figured > > > >>>>>>> (somewhat correctly) that the LEDs would be pretty voltage sensitive. > > > >>>>>> That will require switch mode conversion, no other choice. > > > > >>>>>>> What do you think of this idea? Take an LED driver chip, like an > > > >>>>>>> LM3519 to do the voltage step up and current control, and then three > > > >>>>>>> fets to switch that current to each of the LEDs. Means a chip, a > > > >>>>>>> small inductor and schottkey, a couple of caps, and three fets. > > > >>>>>>> Shouldn't take up too much board space or budget... > > > >>>>>> Nope, it ain't quite that easy. It doesn't have an external sense > > > >>>>>> resistor and, consequently, the "accuracy" to which it holds the current > > > >>>>>> is really horrid. Look at the Iout versus Vin, that's just not good > > > >>>>>> enough. If you want to use a chip (or three) you need to find one with > > > >>>>>> at least and external Rsense. > > > > >>>>>> It is usually easier and less expensive to boost that voltage from the > > > >>>>>> two AA cells to 5V and add the analog current source circuits I > > > >>>>>> mentioned in my other post (one per LED section). The PIC could be > > > >>>>>> supplied directly from the AA cell if it's happy with 2.5V. > > > > >>>>> something like:http://www.national.com/ds/LM/LM2705.pdf > > > >>>>> could be used either as constant current or as high voltage supply > > > > >>>> AFAIK those become iffy unde 2.5V. Something like this could work, and > > > >>>> it's cheap: > > > > >>>>http://www.diodes.com/datasheets/AP6714.pdf > > > > >>>> If Charlie would prefer a nicely regulated 3.3V as well which would be > > > >>>> nice to keep the detector side in check he could use the same chip for > > > >>>> that rail. > > > > >>>>> I think you could have three npns floating on top of a shared sense > > > >>>>> resistor > > > >>>>> to do the switching between leds. > > > > >>>> That's a good option. Just make sure any load change reactions have > > > >>>> petered out when the measurement window cometh. > > > >>> Joerg, et.al. > > > > >>> Ok, I think I like the idea of using the 1253adj in the current > > > >>> feedback mode, with three transistors to switch the anodes of the > > > >>> LEDS. Now, for a really controversial subject - transistor selection! > > > >>> I could just throw 2N2222s in there, but are there any better options > > > >>> available, like logic-level FETs that I should use? Looking through > > > >>> the Digikey selections, I found AO9926B, dual FETS that look pretty > > > >>> good, while still being big enough to solder by hand! > > > > >>> Any good, cheap through hole logic level FETs for prototyping? > > > > >> Don't you need P-channel? These look good but there won't be much in > > > >> through-hole, that era is over: > > > > >>http://www.diodes.com/datasheets/ds30933.pdf > > > > >> But make sure the source doesn't get much above 3.3V or it won't turn > > > >> off and your current regulator could hang. IIRC on of your LEDs may > > > >> require more than 3.3V. So you could, for example, hang a BAV99 up front > > > >> to drop 1.2V and a resistor from gate to source. > > > > >>> Thanks again for all the great advice! > > > > >> As one SW guy put it, we are here to serve :-) > > > > >>> Charlie > > > > >>> (at least, this has been on on-topic discussion... ;-) ) > > > > >> Yeah, amazing, not even the slightest rant. > > > > > Ok, this has been bothering me all night. The circuit is now looking > > > > like > > > > > Vout from regulator > > > > | point A > > > > FET switch > > > > | point B > > > > LED > > > > | point C > > > > FB resistor > > > > | > > > > GND > > > > > (Ok, it isn't ASCII art, but hopefully gets the point across...) > > > > > So, working from the bottom, point C is at 1.21 volts. The green LED > > > > has a Vforward of 3.4V, so B is at 4.6V. I have 3.1VDC (typically) > > > > from the PIC pin to switch the FET. Not an easy problem. > > > > It is easy: Spring for two logic level FETs that are guaranteed to have > > > low Rdson at 3V drive. One P and one N. The P-channel goes where your > > > FET switch ist between points A and B, source to point A. It's gate has > > > a resistor of 10k or whatever to "Vout from regulator". Now place a > > > N-channel, source to GND, drain to gate of the P-channel and it's gate > > > is directly driven by the PIC. > > > > > Unfortunately, the RGB LED is common cathode, so needs to be switched > > > > above, not below, so need to somehow raise the level of the turn on > > > > signal to be able to control the FET, and still be able to turn it > > > > off. Of course, this is just one of three circuits, so I need to be > > > > sure the others don't turn on at the same time... ;-) > > > The RGB LED is common-cathode? Oh. Then this would work: > > > +3.3v > > -+- > > | > > .--------+--------+--------. > > | | | | > > |<' |<' |<' |<' > > -| Q1 -| Q2 -| Q3 -| Q4 > > |\ |\ |\ |\ > > | | | | > > | | | | > > | | LED-R |LED-G | LED-B > > | V ~> V ~> V ~> > > | --- --- --- > > | | | | > > | D1 | | | > > +---|<---+--------+--------' > > | | > > |_ L1 --- C1 > > )|| --- > > )|| | > > _)|| === > > | > > +--->Vsense (to switching current regulator, > > | e.g. ZXSC310) > > .-. > > | | > > | | Rsense > > '-' > > | > > === > > GND > > > This approach is efficient, stable, inexpensive, small, and provides a > > wide-compliance range. It needs no level-translation, which saves six > > parts or so. A resistor-DAC to the Vsense node could modify the > > individual LED currents, if desired. > > > -- > > Cheers, > > James Arthur > > > > > Dang, Sorry I don't get this. I turn on one of the transistors and > nothing happens right away because of the inductor. But current > starts to flow with an L/R time constant... now what? > > George H. Summary: Q1 is the switch for a switching regulator IC. Bang Q1, and it produces a negative current source at the LEDs' common anode. Q2-4 control the individual LEDs. The switcher I suggested--the ZXSC310--is neat because it's cheap and has a very low sense voltage (25mV), reducing losses, but just about any IC would do. -- Cheers! James Arthur |