Distance measuring device questions....

[Ppw]

Hi all, first off, i want to make clear that i am a welder/fabricator. Please forgive me for my lack of knowledge in the electrical field That said, i am working on a project and am wanting to build a measuring device that will be part of the project. The measuring device should be as small as possible, have a working range of min 2-3" to a max of aprox 2'. I am looking at the sharp GP2Y0A21YK which seems to have a range of 4" - 31" which should work fine. I don't need constant measuring, I want to be able to have it be triggered with a button when i am ready to take a measurment and have it send the measurment in mills to a LCD or comparable readout.

My question is, is this possible and am i heading in the right direction with the sharp unit? I can't find any info on accuraccy +- though which is an issue. Is there any info available to a newbie somewhere who is wanting to learn to do such a project? Thanks!

Mitch

 

[vne147]

The sharp until if I'm not mistaken produces an analog output meaning that the voltage output by the sensor changes depending on the distance measured. You must then convert that analog voltage to a number using an analog to digital converter. Last but not least that digital number needs to be fed into a display driver that will produce the correct information on the display. I would recommend using 7 segment LED displays as opposed to LCD if you are building it yourself and using discreet ICs. The best solution in my opinion here would be to use a micro controller. It would be the simplest, smallest, and cheapest circuit. Almost all of the above mentioned steps would be handled via software. I might be willing to help you out with that if interested.

 

[Ppw]

Thanks for posting on this vne147! This may be a premature question, but how much space would the system you propose use? For example, could a system like this be do-able while being able to be mounted in a 2.5" x 2.5" x 1.5" pod? (Just pulling those numbers out of my head but i would like it to be in that ballpark). I would certainly like to talk to you a bit more about this, and yes, I would be interested in getting a quote from you. Feel free to PM me. Thanks!

 

[vne147]

OK, I'll send a PM.

 

[Mr RB]

I don't think it will have the accuracy you want. The best you will get will be within a few percent of actual reading, the Sharp sensor outputs in "voltage steps" generated by its internal controller, I think they are about 1:256 resolution, and non linear so they are more accurate up close and quite poor resolution at a distance.

 

[vne147]

I don't think it will have the accuracy you want. The best you will get will be within a few percent of actual reading, the Sharp sensor outputs in "voltage steps" generated by its internal controller, I think they are about 1:256 resolution, and non linear so they are more accurate up close and quite poor resolution at a distance.

Mr RB,

I agree with the non-linearity but where did you get the information on the 1:256 resolution? I didn't see that anywhere in the data sheet. Thanks.

 

[Mr RB]

It's not listed in the datasheet.

I remember seeing on the net someone had made a jig on a big slide rule, and measured quite accurately and charted the result.
Ok I googled for you, it was David Cook on his excellent RobotRoom.com web site;
Robot Room: Sharp Infrared Distance Sensor Test Apparatus, Page 3

 

[vne147]

Wow that guy really did a thorough job testing the sensor. There was some really good info there. Thanks!