Let's Make Robots!

Location, location, location!

Hello everyone!

Now, I'm sure I can't be the first with this problem. A quick scan of the forums didn't turn up much, so I'll ask outright. I have a semi-autonomous robot project (won't bore with details) and I absolutely NEED to have a coordinate system (X, Y, and the direction the robot is facing). This can't involve any GPS or expensive digital compass sensors, and it needs to be pretty accurate. And because this might be asked, I'm running a twin gearbox Tamiya motor and two rubber wheels. It's a pretty small setup. Someone here has to have run into this before...what are your suggestions or solutions?

Thanks in advance! 

- P 

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Well...I'm breaking down and buying this: http://www.sparkfun.com/commerce/product_info.php?products_id=7915

I need this for my thesis project and can't afford not to have it working. It pains me to have to buy a complete unit rather than make it myself, but I've recently found out that the timeline for this is a lot shorter than I thought. Thanks so much for all of the help with this, that's why I keep coming back :P

- P 

you're breaking my heart. I was really hoping for this to work. :/

Anyway good luck with your project. :)

I'm running a 9V through a 7805 voltage regulator. I don't have a processor on anything yet, was just building it on a breadboard first. I've actually taken apart the setup, but might put it together again later in which case I will upload some pictures. I'll try the cap, thanks for the tip!

- P 

I ordered the A1321LUA-T sensors. Unfortunately, I can't get the setup to work. I'm reading just under 2.5V from both outputs, but I can't get a stable enough signal at the output. I've tried the 100K and 1M feedback resistors, and I'm finding the output jumps from 1.6V to 2.54 at random, but as I rotate the setup, nothing changes. I'm going to have a go at it again tomorrow, but I'm not sure what more to try...

- P 

What power supply are you using. Show us a photo of your setup. The fact that your output is fluctuating indicates that your sensors are probably picking up interferance from you processor. Putting a small capacitor across pins 1 & 8 may improve stability. Start off with about 100pF. This circuit will be sensitive to electrical noise.

I don't understand why it has to be so complex..Basically if you have a magnetic sensor in a horizontal position wouldn't you be able to pick up the earth's magnetic fields? (presuming that there is no stronger magnet close by)

I'm still very interested in making this work, but it seems a bit over my head. Hope you'll put it together and make it work some day you get the time. If anyone can it would be you. It's a brilliant idea and I think a LOT of people would be interested in a cheap DIY compass...

The problem with amplifying what is basically a DC signal is that any offset between the inputs gets amplified as well causing the output to swing all the way to one rail or the other. Any other stray magnetic fields will also be greatly amplified. I suspect that we need a more complex circuit that will eliminate fluctuating signals.

Last time I used hall effect sensors I had the opposite problem, I had to eliminate the effect of the earths magnetic field.

Touché! And yes you may answer...

What a bummer about the setup. Unfortunately I can't be of much help here. Never used one of these things (hall effect sensors). Hopefully OddBot will jump in and say something useful soon...:/

Parts have been ordered...next week is looking like a long ways away! I'll document everything to make a walkthrough if this works out.

- P 

Which hall effect sensors did you end up ordering?

PS: Looking forward to hearing more details :)