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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Ok...so I quickly came up with a circuit this morning that translates the output from the hall effect sensors into a 0-5V range for ADC use. the link has the circuit + calculations, so if anyone sees anything wrong with this, please let me know and I'll correct it. :)

For those thinking of using this as a compass, this is only half of the circuit. Another one is required for the second HES, and I'm working on an algorithm to translate the resulting voltages into a single 0 - 360 degree value. I'll post that once it's done. (hopefully this afternoon)

Once again, thanks for all of the links people!

Circuit and calculations: http://imgur.com/7IP1k.jpg

- P 

EDIT: Yikes...I didn't read through the datasheet properly...That schematic is all wrong...I'll have a new post in a minute!  

EDIT: Ok..I think all I needed to do was remove the bias resistors. It's also now a non-inverting amp. The image linked above is the new schematic with calculations. 

Just wondering what kind of sensor you're planning to use? It would seem that the UGN3503UA that OddBot suggested is no longer in production...

And thanks for posting the circuit. I might use it too :)

OddBots link to his walkthrough had a link to an online supplier who seemed to carry it. I'll double check now. I know sparkfun has a hall effect sensor, but I think it's digital and doesn't give the same kind of response. 

I'm also worried about how sensitive this sensor is going to be...I guess since OddBot is the only one who seems to have used it...would you know if it gives the entire +/-900G as described in the datasheet from the earth's magnetic field?

- P 

In the meantime I found a place that sells the UGN3503U, so I'll be going for that one. 

And I can't help you with your question since I never uses one of these things before and don't know much about them...

Please keep us updated on how this (DIY compass) moves along. I for one am VERY interested in how you manage to make it work :)

I'm going to be placing orders for parts this week, thanks to a new schematic posted here by a very clever person : )

I'll get a video up (I hope..) and all that jazz when I get time, but the project is on a really tight schedule so I have to have it built the day I receive components. You'll hear soon.

Thanks for all the questions/interest/assistance with this everyone!

- P 

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 :)

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