Post by thread:[EE]: Cheap light level sensor

Hey, I'm still thinking about how to sense fuel levels in a fuel tank I'm building. I'm leaning toward the idea of a clear shaft tapered at several lengths. Can anyone suggest a cheap way of sensing the reflected light? The only cheap sensors I can find appear to have a sensing distance of only a few mm at best (I'd be using a ~12" shaft). Am I looking at the wrong type of sensor for this purpose? Thanks, Dave -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email spam_OUTlistservTakeThisOuTmitvma.mit.edu with SET PICList DIGEST in the body

>Hey, >I'm still thinking about how to sense fuel levels in a fuel tank I'm >building. I'm leaning toward the idea of a clear shaft tapered at several >lengths. Can anyone suggest a cheap way of sensing the reflected light? >The only cheap sensors I can find appear to have a sensing distance of only >a few mm at best (I'd be using a ~12" shaft). Am I looking at the wrong >type of sensor for this purpose? > >Thanks, >Dave I would try two approaches: 1. ultrasonic distance measurement - put sender and received on the top of your fuel tank. send chirps and listen the echo to calc the distance 2. capacitive (may be dangerous if not well isolated) - if your tank is with metal walls (it should be if it's fuel tank) put well isolated metal rod inside the tank and make high approx.200kHz frequency generator - the fuel level will change the capacitance of your rod-tank wall system with 10 to 100 pf depend on your tank volume - then all you have to do is to measure the frequency on the output Best regards Tsvetan --- PCB prototypes for $26 at http://run.to/pcb (http://www.olimex.com/pcb) Development boards for PIC, AVR and MSP430 (http://www.olimex.com/dev) -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email .....listservKILLspam@spam@mitvma.mit.edu with SET PICList DIGEST in the body

Range of a light sensor depends almost entirely on the optics of the situation. If your shaft makes a good light pipe (the outside should be polished) you may well get the range you need. Simple amplitude sensing will be cheap and may be good enough. For a little more cost you could flash the light source and measure reflection vs. time. Each step in diameter would produce a reflected pulse of different amplitude depending on whether it is wet or not. I am afraid the timing will be faster than a PIC can handle without hardware help. My suggestion is to build a sensor and try it. Even if it doesn't quite work you will learn a lot. Sherpa Doug > {Original Message removed}

Since what you are really looking for is the level of reflected light, then you can simply use an LED to provide light and a [cds cell, photodiode, LED, etc] to sense the amount of light returning. Any sensor that outputs light and returns information on how much light is returning should work. The few mm sensor should work well, since the light will travel much better and further inside the tube. -Adam Dave VanEe wrote: {Quote hidden}>Hey, >I'm still thinking about how to sense fuel levels in a fuel tank I'm >building. I'm leaning toward the idea of a clear shaft tapered at several >lengths. Can anyone suggest a cheap way of sensing the reflected light? >The only cheap sensors I can find appear to have a sensing distance of only >a few mm at best (I'd be using a ~12" shaft). Am I looking at the wrong >type of sensor for this purpose? > >Thanks, >Dave > >-- >http://www.piclist.com#nomail Going offline? Don't AutoReply us! >email listservKILLspammitvma.mit.edu with SET PICList DIGEST in the body > > > > > -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email .....listservKILLspam.....mitvma.mit.edu with SET PICList DIGEST in the body

The trick that has not been mentioned is to switch the transmitting LED of and on at a suitable frequency, and then use the photodiode with an amplifier. Because you are sensing an AC signal it is a lot easier to get decent gain if you need it. with the right settings this should enable you to sense accurately with minimal component count. -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email EraseMElistservspam_OUTTakeThisOuTmitvma.mit.edu with SET PICList DIGEST in the body

Go capacitive. I think it will be easier in the long run. Here is my favorite book on capacitive sensors of all types: Capacitive Sensors : Design and Applications, by Larry K. Baxter, ISBN: 078035351X. I actually own a copy. LOTS of ideas for different applications in this book. Have fun, Tony {Original Message removed}