Post by thread:[PIC]: Sssssssssssmokin'

Should have very few insects inside a hot oven. I'll also probably build some hysteresis into the thing to ignore bugs or smoke for a short while (many incompetent cooks like to burn their food just before pulling it out. Blackened redfish? Blackened cheese sandwich? ) but finally hit the panic button if it persists. I am mostly looking for the case where the oven is unattended, the food is left for way too long, and we need an emergency shutdown. Right now I am working on punching more current into my IR diode. Looking through my junk box trying to figure out what a low ESR capacitor looks like. I figure dumping current out of a low ESR capacitor using a low RDSon FET should do the trick nicely. May have to break down and order some today. Junk box is running thin. --Lawrence > > They are, but they are somewhat less sensitive to smoke than the > radioactive types. > The crossed path detection mechanism is correct, the fun is in screening > out small reflective insects, without screening out the smoke :) > -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

Uh oh. Optek has been telling me that IR is the way to go. This is bad news. I actually found that my flashlight set off the detector quite well, it is sensitive to visible light as well as IR. I think it is biased toward the red end because a BLUE led will not set it off at all. Maybe all I need is a stupid flashlight bulb instead of a fancy LED. Or just a red LED. I'll try one. --Lawrence {Original Message removed}

> Right now I am working on punching more current into my IR diode. Looking >through my junk box trying to figure out what a low ESR capacitor looks >like. I figure dumping current out of a low ESR capacitor using a low RDSon >FET should do the trick nicely. Generally, a higher voltage cap at a given uF rating, will be lower ESR. -- Where's dave? http://www.findu.com/cgi-bin/find.cgi?kc6ete-9 -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

At 01:09 PM 12/19/00 -0600, Lawrence Lile wrote: >Uh oh. > >Optek has been telling me that IR is the way to go. This is bad news. IR works well to sense smoke. IR isn't attenuated as much (or reflected by, as much) as visible light, but it's pretty easy to exclude near-IR pollution. I'd definitely want to dump that module. I don't think it's buying you anything. -- Where's dave? http://www.findu.com/cgi-bin/find.cgi?kc6ete-9 -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

Of the various designs I've seen (most of which were copyrighted - sigh) the one that sticks had a tube which the smoke passed through. On one end was the sensor (or on both ends) and inside the tube there were holes (actually smaller tubes connected to the larger one) which would shine IR into the tube. the tube interier was flat black, so you'd get a good bit of IR on the sensor only when smoke was present. But this required several IR leds. Rather than pulsing one LED, why not pulse several high power IR leds? Alternately you could use a fine particle filter, filter a bit of the outgoing air and weigh the filter continuously - Ala the chicken weighing problem. Warm up the filter so there's no condensation and viola! ;-) -Adam Lawrence Lile wrote: {Quote hidden}> > Uh oh. > > Optek has been telling me that IR is the way to go. This is bad news. > > I actually found that my flashlight set off the detector quite well, it is > sensitive to visible light as well as IR. I think it is biased toward the > red end because a BLUE led will not set it off at all. > > Maybe all I need is a stupid flashlight bulb instead of a fancy LED. Or > just a red LED. I'll try one. > > --Lawrence > > {Original Message removed}

>Alternately you could use a fine particle filter, filter a bit of the >outgoing air and weigh the filter continuously - Ala the chicken weighing >problem. Warm up the filter so there's no condensation and viola! ;-) That sounds like a cute idea for a micromachine application. -- Where's dave? http://www.findu.com/cgi-bin/find.cgi?kc6ete-9 -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

Lawrence, You may want to look into the PHOTOFLASH QUALITY low ESR caps. Dumping that much energy from any general purpose cap will cause failures after a short time because of the flexing of the plates against the end caps and connections. At least thats what we found in the oil industry anyway. Just food for thought. Granted, I know you're just developing right now, so any cap should be sufficient for that, but when production come around, go for the better cap for more reliability. Regards, Jim On Tue, 19 December 2000, Lawrence Lile wrote: {Quote hidden}> > Should have very few insects inside a hot oven. I'll also probably build > some hysteresis into the thing to ignore bugs or smoke for a short while > (many incompetent cooks like to burn their food just before pulling it out. > Blackened redfish? Blackened cheese sandwich? ) but finally hit the panic > button if it persists. I am mostly looking for the case where the oven is > unattended, the food is left for way too long, and we need an emergency > shutdown. > > Right now I am working on punching more current into my IR diode. Looking > through my junk box trying to figure out what a low ESR capacitor looks > like. I figure dumping current out of a low ESR capacitor using a low RDSon > FET should do the trick nicely. > > May have to break down and order some today. Junk box is running thin. > > --Lawrence > > > > They are, but they are somewhat less sensitive to smoke than the > > radioactive types. > > The crossed path detection mechanism is correct, the fun is in screening > > out small reflective insects, without screening out the smoke :) > > > > -- > http://www.piclist.com hint: The list server can filter out subtopics > (like ads or off topics) for you. See http://www.piclist.com/#topics spam_OUTjimTakeThisOuTjpes.com -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

At 12:54 PM 12/19/00 -0800, James Paul wrote: > Lawrence, > > You may want to look into the PHOTOFLASH QUALITY low ESR caps. > Dumping that much energy from any general purpose cap will > cause failures after a short time because of the flexing of the > plates against the end caps and connections. At least thats > what we found in the oil industry anyway. Just food for thought. > Granted, I know you're just developing right now, so any cap should > be sufficient for that, but when production come around, go for the > better cap for more reliability. He really shouldn't have to go to these extremes. I've seen it done with very simple circuitry. (I used to install them) Synchronus detection, or at least sending a pulse train will help, but I've seen it done with DC. -- Where's dave? http://www.findu.com/cgi-bin/find.cgi?kc6ete-9 -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

Lawrence, since the oven is hot i assume you're placing the electronics and IR emitter/detecter somewhere below 70 degrees C? Are you by chance passing the IR through any sort of glass? Cos if you are, that would explain why your flashlight and a red LED seems to work better. IR gets attenuated through most glass and other optically clear medium. Blue LEDs have little or no wavelengths close to the IR spectrum that's probably why it won't work. Another thought is the heating element in the oven. It'll be emitting heat and some measure of IR as well. That being the case, why not try the reverse of what you're trying to do? Have a light source illuminate a detecter (end to end) through a horizontally mounted tube. Drill a series of holes in the tube to allow a free flow of smoke to pass through the light beam and detect a drop in light level. If costs permits, i would use a microcontroller for better reliability. Instead of just having a preset light level threshold, i'd incorporate a power on self test/calibration to compensate for soot/grease/baked insect build-up in the tube. The light source and detecter's performance will also suffer from ageing and heat over a period of time. A bypass switch would be a nice touch for those who sneak in to reflow solder PCB's when the wife's away. Terry At 01:09 PM 12/19/00 -0600, you wrote: {Quote hidden}>Uh oh. > >Optek has been telling me that IR is the way to go. This is bad news. > >I actually found that my flashlight set off the detector quite well, it is >sensitive to visible light as well as IR. I think it is biased toward the >red end because a BLUE led will not set it off at all. > >Maybe all I need is a stupid flashlight bulb instead of a fancy LED. Or >just a red LED. I'll try one. > >--Lawrence > > >{Original Message removed}

On the advice of most everybody I converted the smoke detector to a photoLED ( Optek OP999) in reversed biased mode. Hook this up to an op-amp, and compare the result to a constant DC voltage. Reverse biased Opto LED's leak more if they are exposed to light, according to theory. This one has 4.7 megohm in series with the reverse biased LED. Supposed to produce about 60 nanoamps dark current (which would drive the whole thing to about 4.7 volts) and maybe 1 microamp light current (driving the thing to about .3 volts) The op amp compares this with a DC signal produced by a pot. Way too high impedances to put into a PIC directly. The IR emitter and detector is arranged in reflective mode, with the detector and emitter 90 degrees from each other, so a reflective object would set them off. In practice, no such thing happens. It makes a great solid object sensor detecting fingers, paper, etc. Won't detect smoke. Had a chat with the OPTEK engineer I'm working with, and this is the arrangement he recommended. Said that the reversed biased LED was much more sensitive than the photologic module I was working with earlier. So far, you can't prove it by me. -- Lawrence "Smokey" Lile -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

The ratio of dark to light current is hard to measure, but I can infer I'm getting about 150 nanoamps dark current, and 595 nanoamps with a solid object in front of the detector. What light current I get with reflected light from smoke I don't know since I've never been able to trigger it with smoke yet.. Remember this arrangement is based on pulsing the IR emitter at high amps for brief periods. I tried an arrangement with a phototransistor and an LED powered with DC yesterday, still no luck. The DC led was probably not bright enough to do any good. All of these have worked fine in detecting solid objects. {Original Message removed}