Thanks Art and all others for your kind help on this subject. /Ake -----Ursprungligt meddelande----- Fr=E5n: pic microcontroller discussion list [mailto:PICLIST@MITVMA.MIT.EDU]F=F6r Art Skickat: den 19 april 2004 15:34 Till: PICLIST@MITVMA.MIT.EDU =C4mne: Re: SV: [EE:]Light detector OK, I think that noise might be an issue-LSR's aren't known for being quiet. I use alot of the Burr-Brown opt201/301 photodiode/integrated amp assembly's in my work, but I need low noise and high sensitivity. I have not tried the Taos parts yet, but they are on my list of devices to try for less demanding aps. If you don't need extreme sensitivity, I suggest you avoid the Burr-Brown parts and go with the TAOS units. The Taos parts have some hysterisis built into them and the photodiode active area is small, so they are less expensive to manufacture. My guess is that they would be just the ticket for you. I'd also guess that you will need some simple software hysterisis too, but you probably have a good handle on that already. To do it right, you probably do need the A/D converter and the programmable hysterisis available from the pic software. Have fun and be sure to get the free samples from TAOS, they are good about that aspect as well. Regards, Art At 04:25 AM 4/19/04, you wrote: >Art, > >I just plan to use it for ambient light levels. Actually I'm only >interested in if there is lights on (sun, lamps) or if its dark. I need >the threshold to be user settable as "dark" is a subjective thing. The >thought is that a node send out a message (VSCP) when the transition >occurs (with hysteresis of course). This message can be used by other >nodes to turn on/off lamps or do other things. > >I found a Light to voltage sensor, TSL250 from TAOS, that was rather low >cost and I will probably use that instead of the LDR. > >For those interested I why I need this: >VSCP, stands for Very Simple Control Protocol and is a very, *very* >simple higher level protocol over CAN/TCP/UDP and such. It is event >driven and all that a node does is that it sends out its event when it >occurs or at even intervals. Other nodes can "do stuff" or react on >this event (light a lamp, log to a database) etc. It's really stupid but >makes a system that is very easy to configure. More information is >available at http://www.vscp.org > >I have been working with this since 1984 (yes I know I'm slow...) when >the node was a 6800 and I think the manufacturing cost was about $250 >and RS-232 was the only communication option. Now the node is based >around a 12F675 or 18F248/258 using CAN and the cost is very low. Still >this is may something that never will be finished but its a fun ride >soldering, thinking about it, trying it out... > >/Ake > >-----Ursprungligt meddelande----- >Fr=E5n: pic microcontroller discussion list >[mailto:PICLIST@MITVMA.MIT.EDU]F=F6r Art >Skickat: den 18 april 2004 22:21 >Till: PICLIST@MITVMA.MIT.EDU >=C4mne: Re: [EE:]Light detector > > >You didn't say what data rate you were trying to receive. LDR's have >really >poor frequency characteristics, don't expect much better than 5 to 20 >Hz, >especially with a 500k series resistor. > >When I first read you message, I thought you were just trying to detect >ambient light levels, but not sure. > >Phototransistors are good for low data rates, up to 10Khz or a tad >higher >if you are using them in small signal mode. Otherwise, look at a >photodiode >for big bandwidth and a very large dynamic range. > >Smile, it can always be worse:>: > >Art > >At 02:05 PM 4/18/04, you wrote: > >I am in need for a low cost light detector that has a use settable > >trigger point for the light/dark threshold. My first thought has been >to > >just set up a voltage divider in the following way. > > > > +5V > > | > > | | > > | | 500K > > | | > > | > > | > > |--------- PIC ADC > > | > > | > > | | > > | | LDR > > | | > > | > > | > > --- > > > >The LDR has >500K resistance in darkness and 3K-20K at 10 Lux. > > > >One could use a PIC output pin to feed the divider instead of the +5V > >and just activate this when a measurement is needed. > > > >Is there any drawbacks with such a scenario? Is there a better way to >do > >this in a low cost way? > > > >/Ake > > > > --- > >Ake Hedman (YAP - Yet Another Programmer) > >eurosource, Brattbergav=E4gen 17, 820 50 LOS, Sweden > >Phone: 46 657 413430 Cellular: 46 730 533146 > >Company home: http://www.eurosource.se Kryddor/Te/Kaffe: > >http://www.brattberg.com > >Personal homepage: http://www.eurosource.se/akhe > > > >-- > >http://www.piclist.com hint: The PICList is archived three different > >ways. See http://www.piclist.com/#archives for details. > >-- >http://www.piclist.com hint: The PICList is archived three different >ways. See http://www.piclist.com/#archives for details. > >-- >http://www.piclist.com#nomail Going offline? Don't AutoReply us! >email listserv@mitvma.mit.edu with SET PICList DIGEST in the body -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email listserv@mitvma.mit.edu with SET PICList DIGEST in the body -- http://www.piclist.com#nomail Going offline? 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