I have had good results using various LEDs as Laser Detectors. Connect LED up to a digital voltmeter and shine Laser onto front of diode. Different types of LEDs give different results. The LED will give you best results when connected to an OPAMP current to voltage converter. This is simply an inverting configuration. (+) to Ground, (-) to LED, other side of LED to Ground. 1 Megohm feedback resistor between output and (-) will yield -1 volt out for each +1 microamp produced by the LED sensor. Reverse LED to reverse output polarity. If you arrange it so that the output goes positive, then you can use a single-supply type OPAMP (use a rail-to-rail type). I generally end up using a 10 Megohm feedback resistor. I have found the RED LEDs to be the best for visible RED Lasers such as the cheap Laser pointers. Again, try different types of RED LEDs to determine what works best with your particular style Laser. I have had best results with clear red units as opposed to diffused red units. By the way, because the LEDs are supplying current into the virtual ground or null point, they operate very fast. Try it. I think you will like it. Fr. Tom McGahee ---------- > From: Tony Nixon > To: PICLIST@MITVMA.MIT.EDU > Subject: Laser detector > Date: Wednesday, August 18, 1999 1:21 AM > > Hi all, > > Previously, I mentioned that I built an amphometer using a 16F84 a dual > comparator and two LDRs. As a vehicle passed over the top of the LDRs, > the light level change altered the output states of the comparators and > the PIC calculated the speed from the difference in time. Pretty simple, > and it was verified with high speed video and is quite accurate. The > problem is varying light levels and the need to compensate for this to > avoid false triggering. > > After much mucking about, I decided to still use the PIC section, but > use 2 laser modules instead so that each beam can be broken as the > vehicle passes. These are only $8 each for a 3-4.5V 5mW device complete > with lens. > > Has anyone used LDRs as a detector for laser light, or should I use > something else? > -- > Best regards > > Tony > > http://www.picnpoke.com > Email sales@picnpoke.com