Bob Engelhardt wrote:> Winston wrote: >> Bob Engelhardt wrote: >>> Doncha' need a current limiter on the LED? > >> Nup. It's a 'shunt regulator'. >> http://en.wikipedia.org/wiki/Linear_regulator#Simple_zener_regulator > > The wiki ckt has a current-limiting resistor in series with the voltage > source. Not so the posted ckt.It *is* in the posted circuit. Sort of. :) As James mentions, the internal resistance of the PV cell is the current-limiting resistor. --Winston <--The BSA B50T POS used a single power zener across the battery as it's only voltage regulator.
Repaired Harbor Freight digital caliper
Started by ●November 19, 2011
Reply by ●November 23, 20112011-11-23
Reply by ●November 23, 20112011-11-23
Winston wrote:> Bob Engelhardt wrote: >> The wiki ckt has a current-limiting resistor in series with the voltage >> source. Not so the posted ckt.> It *is* in the posted circuit. > Sort of. :) > > As James mentions, the internal resistance of the PV > cell is the current-limiting resistor.I meant the capacitor voltage source. Is its internal resistance a sufficient current limiter? I'm not familiar with super caps, but the common ones that I am familiar with will supply huge currents, momentarily. Bob
Reply by ●November 23, 20112011-11-23
dagmargoodboat@yahoo.com wrote:> On Nov 23, 4:03 pm, Winston <Wins...@BigBrother.net> wrote: > >>dagmargoodb...@yahoo.com wrote: >> >>(...) >> >> >>>I saw a solar-powered Mitutoyo at a flea market and was intrigued, but >>>resisted. >> >>Next time, advise jump on it before someone else does. >> >>I have two of those. They just keep working without >>any issues. Well, except for turning off in low-light >>situations. I just charge it up with the flashlight >>and it works just fine. 'Way better than having to >>run to the store for a $5 battery! They are fine tools >>and have my highest recommendation. > > > Yes, but I got one of the HF's and hacked it up with a Dremel tool, to > mount to the lathe. > > Can't do that with a Mitutoyo! > > -- > Cheers, > James ArthurHey, that's one hell of an idea! :) Jamie
Reply by ●November 23, 20112011-11-23
Bob Engelhardt wrote:> Winston wrote: >> Bob Engelhardt wrote: >>> The wiki ckt has a current-limiting resistor in series with the voltage >>> source. Not so the posted ckt. > >> It *is* in the posted circuit. >> Sort of. :) >> >> As James mentions, the internal resistance of the PV >> cell is the current-limiting resistor. > > I meant the capacitor voltage source. Is its internal resistance a > sufficient current limiter? I'm not familiar with super caps, but the > common ones that I am familiar with will supply huge currents, momentarily.This circuit, yes? D1 .--|>|--+-----+----> (+) to caliper + | | | .------. + | | | | --- --- | ---- | --- \ / ~~> | | C1| --- | ---- | | | LED (red) | | | | '------' | | - | PV | | '--------+-----+---> (-) to caliper Under no circumstances would the voltage across the LED (and capacitor) go above, say 1.8 V because the LED turns any additional voltage into current. In order for C1 to produce a current large enough to endanger the LED or the caliper, it would have to be allowed to charge significantly above the 'zener point' of the LED. It just cannot. --Winston
Reply by ●November 23, 20112011-11-23
On 11/23/2011 4:56 PM, Bob Engelhardt wrote:> John S wrote: >> On 11/23/2011 2:05 PM, Bob Engelhardt wrote: > >>> Doncha' need a current limiter on the LED? > >> >> Not if the PV cell's rated SC current is less than the max LED current >> rating. > > Isn't the capacitor's rated current MUCH more than the LED's? BobWhat has that to do with it? The voltage is clamped. What are you missing?
Reply by ●November 23, 20112011-11-23
I get my LR44's and CR2032's here: http://www.infinitelights.com/alkalinewatchbatteries.html Orders > $20 ship free. I use more CR2032's.
Reply by ●November 23, 20112011-11-23
Winston wrote:> This circuit, yes? > > D1 > .--|>|--+-----+----> (+) to caliper > + | | | > .------. + | | > | | --- --- > | ---- | --- \ / ~~> > | | C1| --- > | ---- | | | LED (red) > | | | | > '------' | | > - | PV | | > '--------+-----+---> (-) to caliper > > > Under no circumstances would the voltage across > the LED (and capacitor) go above, say 1.8 V > because the LED turns any additional > voltage into current. ...Oh ... right ... yeah. Dope slap for me. Bob
Reply by ●November 24, 20112011-11-24
Bob Engelhardt wrote:> Winston wrote: >> This circuit, yes?(...)>> Under no circumstances would the voltage across >> the LED (and capacitor) go above, say 1.8 V >> because the LED turns any additional >> voltage into current. ... > > Oh ... right ... yeah.We are all here to learn. :) --Winston
Reply by ●November 24, 20112011-11-24
> > I suppose nobody under fifty knows how to read a real vernier, or a slide > rule for that matter ;-( >Unfortunately, most of us have to use a digital vernier, because we can't SEE the real vernier!
Reply by ●November 24, 20112011-11-24
On Wed, 23 Nov 2011 06:45:46 -0800 (PST), dagmargoodboat@yahoo.com wrote:>The max. solar panel voltage doesn't matter--the LED regulator clamps >the solar panel voltage, taking care of that.Yeah, but shunt regulators and leaky super-caps are not really appropriate for micropower devices. They waste power. In a previous message, James Arthur measured: Drain: 13.5uA (off), 14.5uA (on) Battery low threshold (blinking display): 1.37V Lowest operating voltage: 1.01V Nominal voltage on a silver oxide battery is 1.5V. Therefore, the operating power is: 1.5VDC * 15uA = 22.5 microwatts. From the standpoint of a resistive load, that's about: 1.5VDC / 15 uA = 100K ohms The first question is whether a small solar cell will product 22.5 microwatts. Testing a somewhat oversized polycrystaline cell that I found in my junk box (quality unknown), it produces 3.0VDC at 6ma with a short circuit load (my milliamps guesser). My guess(tm) is that this cell is about three times as big as will conveniently fit on the calipers, so I'll just cut the current to 2ma . Delivered power with my desk lamp is 6 milliwatts. Yeah, it will a 22.5 microwatt load. The next question is for how long will it run? Assuming the calipers can handle 3.0VDC without damage, how long will a junk 100UF electrolytic cap run the calipers? <http://www.kpsec.freeuk.com/capacit.htm> From 1.37V is roughly 50% of full 3.0VDC charge. That's about 80% of 1RC time constant. 1RC is: 0.8 * 100K * 1000uF = 80 seconds That's probably enough to make a few measurements. Any longer and a super-cap will probably be needed. Picking 50% of full charge out of the hat is rather convenient, as it makes the time to charge from zero to the dropout point the same 80 seconds (yes, I'm lazy). Whether the user really wants to wait 1.5 minutes under a desk lamp for the calipers to be usable is dubious. Of course, a longer run time, means a longer charge time. For example, a 1F 5V 1ua leakage super-cap, will run the calipers for 80,000 seconds, but will also take 80,000 seconds to charge. There are low voltage DC-DC boost/buck switching regulator chips available that can tolerate a wide range of input voltages, and deliver a constant 1.5VDC. In my never humble opinion, what makes more sense is to do it exactly like the typical solar powered calculator. They all have one or two LR44 batteries inside. However, the solar cell does NOT charge the battery. When you turn the calculator on, and there's enough light to run from the solar cell, the battery is essentially disconnected. When there's not enough light to run the calculator, it runs off the battery. No waiting to charge a capacitor from the solar cell. If you're into high tech, there are various energy scavenging devices that can also power the calipers. <http://en.wikipedia.org/wiki/Energy_harvesting> With only 22.5 microwatts required, it might be possible to power the device with a wind up key, piezo pressure, body heat, kinetic magnetic generator, etc. I kinda like the idea of a wind up caliper. Happy Day of the Turkeys. -- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558
