"dungaree" <matilda@downunder.biz> wrote in message news:iHc8g.75088$H71.14012@newssvr13.news.prodigy.com...> Point the LEDs at one another. Digital data should easily > be transferred half-duplex in both directions.Yeah, I did that for a class project some years ago... 1Mbps was fairly easy with pedestrian op-amps doing the heavy lifting, although I had read Phil Hobb's notes on noise in photodetectors to optimize the design somewhat (they helped so much I decided to go out and buy his book). The original goal was to have a full-duplex system via time-division multiplexing, but I ran out of time to do it (initially synchronizing the two ends when they're first turned on takes a bit of effort), so instead I just had a toggle switch that turned everything around. Getting way off-topic here: At the time I argued something along the lines of how RS-232 to fiber optic converters are often used for long distance links in harsh environments (e.g., production floors), and how requiring only one fiber rather than two would save costs. I realize these days that, while, sure, it does save costs, in many plants the labor of installing *any* sort of link completely outweighs the costs of the actual fiber, associated hardware, etc. I do know of a couple of plants where this wouldn't be the case, though -- a sawmill here in Oregon where the owner has literally dozens of little microcontroller-based projects running the place that he designed himself (most are just soldered together on perfboard because they're all one-offs), and a glass factory in Wisconsin where the entire float glass line is overseen by a single PC... running a DOS program designed some time in the late-'80s! (If you asked someone to design such a system for you, these days the response would probably involve multiple PLCs, multiple PCs, etc...) ---Joel Kolstad
using a LED as a light sensor
Started by ●May 6, 2006
Reply by ●May 10, 20062006-05-10
Reply by ●May 10, 20062006-05-10
On Tue, 9 May 2006 23:30:02 -0400, "mc" <look@www.ai.uga.edu.for.address> wrote:>"dungaree" <matilda@downunder.biz> wrote in message >news:iHc8g.75088$H71.14012@newssvr13.news.prodigy.com... >> Seems one could take advantage of opto ability of LEDS >> as a bi-directional optical data coupler. >> >> Point the LEDs at one another. Digital data should easily >> be transferred half-duplex in both directions. >> >> Cool. > >Invented, I think, by Forrest Mims about 25 years ago, and the subject of a >patentability dispute, or something. Google it.I didn't know he invented the idea, but I have his book describing the technique. I think he recommended heatshrink tubing to seal them into a unit. A related idea was used in a microbarometer project in Scientific American's Amateur Scientist column many years back. It used a pair of LEDs to monitor the height of a meniscus of DOT brake fluid in a glass tube for an on/off control loop. Jon
Reply by ●May 10, 20062006-05-10
On 2006-05-08, John Larkin <jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:> Random yellow T-1 LED, -9 volt bias, full sunlight, 2 uA. As a pv, it > makes 1.5 volts into a 10 meg fluke, pointed at the sun, but only > about 7 mv in office/room light.I stuck a 1N914 (glass encapsulated silicon signal diode) under a burning glass a few years ago and got a few milivolts... it'd probably be much more If I had used a high impedance meter. Bye. Jasen
Reply by ●May 10, 20062006-05-10
On Wed, 10 May 2006 10:52:43 -0000, Jasen Betts <jasen@free.net.nz> wrote:>On 2006-05-08, John Larkin <jjlarkin@highNOTlandTHIStechnologyPART.com> wrote: > > >> Random yellow T-1 LED, -9 volt bias, full sunlight, 2 uA. As a pv, it >> makes 1.5 volts into a 10 meg fluke, pointed at the sun, but only >> about 7 mv in office/room light. > >I stuck a 1N914 (glass encapsulated silicon signal diode) under a burning >glass a few years ago and got a few milivolts... it'd probably be much >more If I had used a high impedance meter.I once built a high input impedance amplifier and used two 1N914/1N4148 (or similar diode with transparent case) to limit the input voltage range between Gnd and Vcc. I noticed sudden voltage fluctuations when working with the circuit and suspect some oscillation problems. It took a while, before I realised that the fluctuation occurred, when my finger was close to one of the diode, shading the light from the lamp. The illuminated diode generated a larger current, which caused the fluctuation. Putting black tape on the diodes solved the problem. The moral of the story is to use non-transparent cases in circuits with high impedance levels. Paul
Reply by ●May 10, 20062006-05-10
On Wed, 10 May 2006 23:55:15 +0300, Paul Keinanen <keinanen@sci.fi> wrote: [snip]> >I once built a high input impedance amplifier and used two >1N914/1N4148 (or similar diode with transparent case) to limit the >input voltage range between Gnd and Vcc. I noticed sudden voltage >fluctuations when working with the circuit and suspect some >oscillation problems. > >It took a while, before I realised that the fluctuation occurred, when >my finger was close to one of the diode, shading the light from the >lamp. The illuminated diode generated a larger current, which caused >the fluctuation. > >Putting black tape on the diodes solved the problem. The moral of the >story is to use non-transparent cases in circuits with high impedance >levels. > >Paul >Heat shrink tubing works nicely for such situations. ...Jim Thompson -- | James E.Thompson, P.E. | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona Voice:(480)460-2350 | | | E-mail Address at Website Fax:(480)460-2142 | Brass Rat | | http://www.analog-innovations.com | 1962 | I love to cook with wine. Sometimes I even put it in the food.
Reply by ●May 10, 20062006-05-10
dungaree wrote:> Seems one could take advantage of opto ability of LEDS > as a bi-directional optical data coupler. > > Point the LEDs at one another. Digital data should easily > be transferred half-duplex in both directions.I have written long threads about this in other groups before. My simple led communications circuit connects a single led to a pair of transistors, one npn, one pnp. To get the most out of the led in receiving mode it is connected directly* to the base of a grounded-emitter npn. This way the led is loaded up which is needed for higher speed coms and the npn is quite happy as it is after all a current amplifier. For transmitting I run a pnp from the supply down to the led via a current limit resistor. Because this would be clamped by the receiving npn *I use a 10K in the base of the npn which has negligible effect in receive mode. Of course this circuit is short-range up to a few meters and can be affected by direct sunlight but is well suited for indoor use such as a hand-held instrument to machine interface. The single led coms circuit (I hate trying to do ASCII circuits) +V +V | | E 10K PNP B ----1K---< TxD | C | | |-----> RXD 100R | | C |--------------10K----- B NPN | E | | + | LED | - | | | GND GND BTW, for daylight and fluro sensing I use clear green leds. *Peter*
Reply by ●May 10, 20062006-05-10
On Wed, 10 May 2006 23:55:15 +0300, Paul Keinanen <keinanen@sci.fi> wrote:>On Wed, 10 May 2006 10:52:43 -0000, Jasen Betts <jasen@free.net.nz> >wrote: > >>On 2006-05-08, John Larkin <jjlarkin@highNOTlandTHIStechnologyPART.com> wrote: >> >> >>> Random yellow T-1 LED, -9 volt bias, full sunlight, 2 uA. As a pv, it >>> makes 1.5 volts into a 10 meg fluke, pointed at the sun, but only >>> about 7 mv in office/room light. >> >>I stuck a 1N914 (glass encapsulated silicon signal diode) under a burning >>glass a few years ago and got a few milivolts... it'd probably be much >>more If I had used a high impedance meter. > >I once built a high input impedance amplifier and used two >1N914/1N4148 (or similar diode with transparent case) to limit the >input voltage range between Gnd and Vcc. I noticed sudden voltage >fluctuations when working with the circuit and suspect some >oscillation problems. > >It took a while, before I realised that the fluctuation occurred, when >my finger was close to one of the diode, shading the light from the >lamp. The illuminated diode generated a larger current, which caused >the fluctuation. > >Putting black tape on the diodes solved the problem. The moral of the >story is to use non-transparent cases in circuits with high impedance >levels. > >Paul >The early GE plastic transistors used a beige translucent epoxy. Just when you had your diffamp all tuned up, microvolts of offset, the boss would step up behind you to check your progress, block the light, and mess it all up. Fluorescent lights would cause "unexplainable" hum, too. John
Reply by ●May 11, 20062006-05-11
On Thu, 11 May 2006 09:05:26 +1000, Peter Jakacki <peterjak@tpg.com.au> wrote: [Snipped]> >The single led coms circuit (I hate trying to do ASCII circuits) >Download AACircuit from http://www.tech-chat.de/index.html This is a CAD to draw ASCII circuits. Regards Anton Erasmus
Reply by ●May 11, 20062006-05-11
Anton Erasmus wrote:> <peterjak@tpg.com.au> wrote: > > [Snipped] >> >> The single led coms circuit (I hate trying to do ASCII circuits) >> > Download AACircuit from http://www.tech-chat.de/index.html > This is a CAD to draw ASCII circuits.A very nice package. I have v 1.28.6 here, from about a year ago. Has it changed to any great extent? -- Some informative links: news:news.announce.newusers http://www.geocities.com/nnqweb/ http://www.catb.org/~esr/faqs/smart-questions.html http://www.caliburn.nl/topposting.html http://www.netmeister.org/news/learn2quote.html
Reply by ●May 15, 20062006-05-15
On Thu, 11 May 2006 12:52:35 -0400, CBFalconer <cbfalconer@yahoo.com> wrote:>Anton Erasmus wrote: >> <peterjak@tpg.com.au> wrote: >> >> [Snipped] >>> >>> The single led coms circuit (I hate trying to do ASCII circuits) >>> >> Download AACircuit from http://www.tech-chat.de/index.html >> This is a CAD to draw ASCII circuits. > >A very nice package. I have v 1.28.6 here, from about a year ago. >Has it changed to any great extent?The latest one still seem to be V1.28.6 beta. Regards Anton Erasmus
