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I'm getting sick of Sharps --Is there something better?

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By Chris the Carpenter

May 21, 2009
Chris the Carpenter's picture

Alright, this is it... I am anti-sharp distance sensor. I spent over a week fighting noise on the power side which screwed with my RF reciever. I have fried them because thier pin-out does not match the configuration of a servo connector or the picaxe 28x board. Thier numbers jump all over the place. Now it seems that all four of the ones I have are "worn-out". By that I mean this:

I added a .1uf cap to deal with noise and now it seems they won't output anything without the cap attached. My picaxe will not sync while even just one sensor is plugged in. On top of that, all of them are spitting out a measurement of 50 or so when looking at infinity and the total sensing distance is down to about 10 or 12 inches maybe less. I am sick of dealing with these silly things and do not want to spend more money replacing the ones I have.

The Problem:

I have to have a minimum of 3 sensors on Walter to deal with his width. A SRF05 centered on a servo is a given thus leaving the needed sensors to catch the corners and sides. I have looked at other sonar systems (the ones with just the single black emitter (SRF02?) and even thought about just spending the bucks on 2 more SRF05's. The issue is (especially with the "single emitter" (which fire constantly)) is interference from sensor to sensor. In many instances I will have 2 sensors firing almost directly forward and the ultrasound from one will screw with the readings of the others. (All 3 sensors must be able to turn via servo). I have looked into some of our fellow LMR'ers IR distance systems but I just can't seem to get the distance I need.

What the hell can I do here?!?! Does anyone know of an upgraded Sharp? Is there a quality IR distance sensor out there? Something? Maybe a 180 degree sensor that does not have to be swept with a servo? 

Oh, and I don't have a lot of cash. 

For the love of God, help.

 

Just had a thought:

Has anyone tried any of the home made IR distance sensors with a lens or two to increase distance/ sensitivity? --Maybe I should experiment a bit...

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By Chris the Carpenter
@ Sun, 2009-05-24 19:58
Chris the Carpenter's picture
I hadn't thought of that... Why didn't I? And you are right about the limited current allowed to run directly through a picaxe output. Transistors, here I come.
By OddBot
@ Mon, 2009-05-25 00:55
OddBot's picture
At the end of my tutorial on LEDs you will find information on how to do this.
By Chris the Carpenter
@ Sun, 2009-05-24 16:04
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I am. I am running 2 in parallel with no resistor! No, I think it has to do with phase timing. I am still a little wishy-washy on the concept, but basiclly there are 2 loops of cycles overlapping eachother. A 38kz signal so the sensor works and a 1khz gate on top of that. I am using pulsin on a second picaxe for testing and I discovered that my limited range of numbers coming in is due to the fact that they are getting too big and too little and "looping" -i.e. if it is a byte variable I am using and the number is bigger than 255 it loops back to 0. I think this should just be a matter of playing with the 1000kc part of things to get that final pulse width into somthing more middle-of-the-road. Again, this does indeed work. I think the next step is to add a pot or two so I can fine adjust on the fly.
By robologist
@ Sun, 2009-05-24 19:02
robologist's picture
If you are running the IR LEDs off a PICAxe pin delivering PWM, then you are not driving them to the edge. The PIC will only output about 25 mA per pin. If you are driving the LEDs through a line driver like the ULN2803 with it's own power, then you might be pretty close, even overdriving since those outputs are capable of delivering more current.
By Chris the Carpenter
@ Sat, 2009-05-23 21:36
Chris the Carpenter's picture

Well, I skipped the 556 and instead used the PWM and a simple 1ms pause on and off for the other cycle. I am gettng results.

So far, I am looking at about a 18" range and a limited range of numbers coming in. Never the less, it is indeed showing a number proportional  to the distance of a white piece of paper held in front of the sensor. I'm going to keep doing some tweaking but proof of concept is indeed there. In addition, I am using a 08m so if this turns out to be a usable system, the evenual PCB should be nice and compact --Servo mountable.

By robologist
@ Sun, 2009-05-24 15:49
robologist's picture
For greater range, you might try driving the LED closer to it's edge of specs.
By mintvelt
@ Sat, 2009-05-23 23:02
mintvelt's picture
I like 08Ms! SHARPs ... boooh.... go PWM!
By Chris the Carpenter
@ Sat, 2009-05-23 01:52
Chris the Carpenter's picture
I have just re-read the post a couple times and man, even with my total lack of knowledge on the subject I think I could actually get this going. I mean, with no exterior help. --Not that I still couldn't use it...
By voodoobot
@ Sat, 2009-05-23 02:31
voodoobot's picture

it does sound interesting, just need to research more on the pll aspect of it.

and google is your friend...

http://www.geocities.com/lemagicien_2000/elecpage/irvis/irvis.html

By Chris the Carpenter
@ Sat, 2009-05-23 01:32
Chris the Carpenter's picture

Ok, circuit gurus...

Picaxe can input a pulse width with no problem. And Salvage seems to have given you guys a ton of usful information here...

The question is, why have you guys not already drawn up a schematic, jpeg'ed it, uploaded it, explained it, shown me how to input it to a picaxe, and given me a code snippit? :)

Seriously though, In my brain I understand fully what is going on here with this system --However with no elec. engineering background... I mean, I don't even know how to calculate what capacitor will give a 38k or 40khz signal. (Begging now) is there anyone out there that can make this a little more tangable? 

God Bless and Go forth.

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