Has anyone thought of using pyro detectors. These are the detectors used in the outside security lights when they detect motion. The detection circuit in these lights is low voltage and probably could be used. ----- Original Message ----- From: "Giles Honeycutt" To: Sent: Tuesday, August 21, 2001 8:03 AM Subject: Re: [OT] Crocking Frog, People sensor > Adam, > From what I am thinking, a op-amp would be a battery drain unless I use a > high dollar low current device. Perhaps coupling the raw signal (from what > ever) to a np cap directly into a port pin of a sleeping PIC. Wake on > change and... Sounds too easy and cheep... > A photo-transistor... If I use a high value resistance on the collector, it > would limit the current draw. Or on a CDS I see one in the Allied catalog > with a range of 100K - 10Meg... That is a little extreme, what is the input > impedance of a PIC input.... Guess it is time to play and see what I can > do.. I am trying to find the trip voltages for a PIC input and current > leakage... Ok current leakage is 1 uA plus or minus. Now the trip voltage, > looks like 0.15VDC & 0.85XVDD. Too large a range for passive AC coupling.. > I will get back to this later when I have more spare time. > > Best regards, > Giles > > > >From: "M. Adam Davis" > >Reply-To: pic microcontroller discussion list > >To: PICLIST@MITVMA.MIT.EDU > >Subject: Re: [PICLIST] [OT] Crocking Frog, People sensor > >Date: Mon, 20 Aug 2001 21:30:48 -0400 > > > >It sounds to me as though you've got the basic idea. > > > >Use a CDS cell or phototransister in a configuration where it outputs a > >voltage corresponding to light level. > > > >(simplified) > >This voltage level goes two places > >1) into a diode/capacitor high pass filter which then leads to an opamp > >2) through a diode into the other opamp input > > > >The output of the opamp is the derivative of the signal, ie how fast the > >signal is changing. A fast change (from light to dark) results in a > >high voltage, where a slow change results in very little voltage. A > >change from dark to light is a high voltage in the opposite polarity. > >This can go directly to a schmidt trigger. > > > >Saturation is not an issue if you pick the right components for the > >light levels you're expecting, and even then it doesn't matter much. > > > >If the signal is steady, the charge on the cap is equal to the signal > >from the light sensor, and the opamp has a difference of 0 to multiply. > >This is the case whether the sensor is saturated or not. If the sensor > >is saturated, then the light can change dramatically within the range of > >saturation and not trigger the device, but that is a simple problem of > >determining reasonable light levels to design for. > > > >-Adam > > > > > > > > > >Giles Honeycutt wrote: > > > >>OK, their is a 100 ways to do this, but I don't want to re-invent the > >>wheel. > >> Are their any reference designs for something like the crocking frog > >>that > >>makes noise when someone walks in front of it? Are they using a > >>photo-resistor and sensing change with a low pass filter? Are they > >>using a > >>photo diode? Photo Transistor? If so, how do they avoid total > >>saturation? > >> > >>Best regards, > >>Giles > > > >-- > >http://www.piclist.com hint: PICList Posts must start with ONE topic: > >[PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads > > > > > > > _________________________________________________________________ > Get your FREE download of MSN Explorer at http://explorer.msn.com/intl.asp > > -- > 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 > > -- 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