tag:blogger.com,1999:blog-2807403883562053852.post3392331945804195406..comments2024-03-27T08:40:31.785-06:00Comments on Clayton Cramer.: Next Obscure Electrical QuestionClayton Cramerhttp://www.blogger.com/profile/03258083387204776812noreply@blogger.comBlogger15125tag:blogger.com,1999:blog-2807403883562053852.post-34897730099515636002018-10-23T12:43:46.653-06:002018-10-23T12:43:46.653-06:00One more thought... Since you are using this to te...One more thought... Since you are using this to tell battery state, you obviously don't want to deplete the battery too much from this circuit. The way to avoid that is to use a higher resistance, which will result in less current through the LED, but also a less bright LED. If you are doing this on your astronomy stuff, where you would be in the dark, a very dim LED (high resistance value) might be best. I'd fiddle with it - get a few resistors of various sizes, or a variable resistor, and see what works best.StormCchaserhttps://www.blogger.com/profile/02998174514362089471noreply@blogger.comtag:blogger.com,1999:blog-2807403883562053852.post-80156873893469680972018-10-22T12:07:56.620-06:002018-10-22T12:07:56.620-06:00I would strongly urge you to put in a resistor, to...I would strongly urge you to put in a resistor, to protect the LED. The LED will have a maximum current rating, so you could calculate the resistor value to allow up to that rating for a drop of, say, one volt, and you should be safe.<br /><br />The resistor value comes from Ohms Law: R = E/I: resistance in ohms = voltage (1V) divided by maximum allowed current in Amperes (not milli-Ampteres). So if the maximum current was, say, 20 mA, use 1/.02 = 50 ohms.<br /><br />JohnStormCchaserhttps://www.blogger.com/profile/02998174514362089471noreply@blogger.comtag:blogger.com,1999:blog-2807403883562053852.post-65188198537291200262018-10-22T07:51:47.884-06:002018-10-22T07:51:47.884-06:00So from reading https://www.radio-electronics.com/...So from reading https://www.radio-electronics.com/info/data/semicond/leds-light-emitting-diodes/characteristics.php, it appears that a red LED with leads across the contacts on the battery pack will light up in the 1.6-2.0 VDC range. No resistor needed? That is all that I need.Clayton Cramerhttps://www.blogger.com/profile/03258083387204776812noreply@blogger.comtag:blogger.com,1999:blog-2807403883562053852.post-18814654582133042092018-10-22T07:44:33.027-06:002018-10-22T07:44:33.027-06:00StormCchasr: Over several tenths of a volt is no p...StormCchasr: Over several tenths of a volt is no problem. Can I leave the resistor out, and just pick an LED that lights up about in the range I want?Clayton Cramerhttps://www.blogger.com/profile/03258083387204776812noreply@blogger.comtag:blogger.com,1999:blog-2807403883562053852.post-33373253969197150082018-10-21T20:23:53.498-06:002018-10-21T20:23:53.498-06:00I could design a circuit to do that to whatever pr...I could design a circuit to do that to whatever precision was needed, but it's probably more than you want to do. <br /><br />With no resistor, or with a resistor, the LED won't go from off to full brightness at one voltage - there will be a range of a few tenths of a volt over which that takes place. The second link has a table giving the "threshold" voltage for given LED colors - but with the caveat that the threshold isn't perfectly sudden.<br /><br />You might find parts of the page at the link below to be useful. <br /><br />And... there are Lithium and also NiMh batteries. I use rechargeable NiMh in my Mac's Bluetooth keyboard.<br /><br />http://www.gizmology.net/LEDs.htm<br /><br />https://www.radio-electronics.com/info/data/semicond/leds-light-emitting-diodes/characteristics.phpStormCchaserhttps://www.blogger.com/profile/02998174514362089471noreply@blogger.comtag:blogger.com,1999:blog-2807403883562053852.post-75550409872467297712018-10-21T19:41:00.446-06:002018-10-21T19:41:00.446-06:00StormCchasr: Don't need variable brightness. O...StormCchasr: Don't need variable brightness. On/off at 2 VDC is all I need.Clayton Cramerhttps://www.blogger.com/profile/03258083387204776812noreply@blogger.comtag:blogger.com,1999:blog-2807403883562053852.post-17596192201482328172018-10-21T19:39:57.782-06:002018-10-21T19:39:57.782-06:00Jim: precision not needed. As long as the voltage...Jim: precision not needed. As long as the voltage is >= 2 or thereabouts.Clayton Cramerhttps://www.blogger.com/profile/03258083387204776812noreply@blogger.comtag:blogger.com,1999:blog-2807403883562053852.post-67697036100341772522018-10-21T19:38:30.423-06:002018-10-21T19:38:30.423-06:00ZendoDeb: Battery tester requires removing the end...ZendoDeb: Battery tester requires removing the end cap and pulling the battery pack.Clayton Cramerhttps://www.blogger.com/profile/03258083387204776812noreply@blogger.comtag:blogger.com,1999:blog-2807403883562053852.post-66818138810991267592018-10-21T19:36:54.310-06:002018-10-21T19:36:54.310-06:00RS: There are lithium AAA batteries?RS: There are lithium AAA batteries?Clayton Cramerhttps://www.blogger.com/profile/03258083387204776812noreply@blogger.comtag:blogger.com,1999:blog-2807403883562053852.post-52187982737244621832018-10-21T15:39:05.601-06:002018-10-21T15:39:05.601-06:00If you are going to get additional resistors, get ...If you are going to get additional resistors, get larger ones, not smaller ones. LEDs will glow on remarkably low current. That LED is capable of tolerating 20 mA. It will probably glow visibly on closer to 2 mA. I would try the included resistors before going to a smaller resistor.<br /><br />Best of luck!<br />WayneWayne Johnsonhttps://www.blogger.com/profile/07652553584958469329noreply@blogger.comtag:blogger.com,1999:blog-2807403883562053852.post-31461749516759904662018-10-21T13:40:38.236-06:002018-10-21T13:40:38.236-06:00Not going to work. Lithium batteries under zero lo...Not going to work. Lithium batteries under zero load have very little voltage drop until they are almost all the way discharged. Lead acid batteries have a nice voltage/charge curve, but li, nope.RShttps://www.blogger.com/profile/06584323173315846013noreply@blogger.comtag:blogger.com,1999:blog-2807403883562053852.post-37541758430579245662018-10-19T16:21:33.830-06:002018-10-19T16:21:33.830-06:00Not sure if https://www.radioshack.com/ can help y...Not sure if https://www.radioshack.com/ can help you out. (The stores closed, but they remain in business on the web.<br /><br />https://www.digikey.com/ should have everything you need, but you might not be able to buy just one.<br /><br />Then there is Parts Express https://www.parts-express.com/cat/electronic-parts/10<br /><br />There are more choices. Depends on the part and the order quantity.<br /><br />But wouldn't your needs be serviced best by a battery tester?Zendo Debhttps://www.blogger.com/profile/00094772654735415974noreply@blogger.comtag:blogger.com,1999:blog-2807403883562053852.post-69616737557480899322018-10-18T20:59:45.166-06:002018-10-18T20:59:45.166-06:00Yes. LED's are diodes, and they only start sig...Yes. LED's are diodes, and they only start significant conduction (pulling enough current to emit much light) at a critical voltage.<br /><br />You cannot judge voltage well using the brightness of an LED. As the voltage goes down, the brightness will change very little, until it suddenly drops rapidly to nothing.<br /><br />If you need to judge brightness, you have to put a resistor in series. BUT... that only works for voltages above the LED's threshold voltage.<br /><br />NOTE: that threshold is not perfectly sudden, but the current is an exponential function of voltage that does a pretty good job of simulating a perfect threshold.StormCchaserhttps://www.blogger.com/profile/02998174514362089471noreply@blogger.comtag:blogger.com,1999:blog-2807403883562053852.post-33499503991876581662018-10-18T17:44:07.318-06:002018-10-18T17:44:07.318-06:00LEDs work on quantum electro-optical principles. A...LEDs work on quantum electro-optical principles. As such, they have a minimum voltage below which they do not emit light at all. The minimum depends on the LED material and the color of light it emits. Longer wavelengths (such as red) are lower energy per photon and need less voltage to light up. That's why blue LEDs may need over 3V while red ones do well with 1.7 or so.<br /><br />That said, they don't have a sharp turn-on at that voltage so I wouldn't rely on it being very precise.<br /><br />One simple way to keep battery drain to a minimum is to enable the LED circuit with a momentary action pushbutton switch ("press to test").Jim Hornhttps://www.blogger.com/profile/00532755731811413741noreply@blogger.comtag:blogger.com,1999:blog-2807403883562053852.post-24946369969312067372018-10-18T14:51:38.734-06:002018-10-18T14:51:38.734-06:00Pretty much any LED has a minimum forward voltage....Pretty much any LED has a minimum forward voltage. You also want to include a series resistor, as otherwise the current drawn by the LED can climb very rapidly with voltage. Possibly tie it with a momentary push button so it only lights when you push the button. If you look on mouser, newark or digikey, you can usually search by forward voltage.Wayne Johnsonhttps://www.blogger.com/profile/07652553584958469329noreply@blogger.com