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squide
01-13-2004, 08:01 PM
This is from a previous post, and I'm including the "Electrical" part of the query into this forum:

Hey everyone! I'm having a few problems with the EDURobot, and I was hoping I could get a little help here.

Banner Sensors (QS18VN6LV) - We learned that the first sensor we worked with was bad (after a week or so), and after getting our second one to work it also went bad. We have a third sensor working, but in summary it's been a pain. After looking through the manuals for the sensors, we learned that the sensors were not working due to an "output overload" (blinking green light). One sensor blinked when it detected dark, the other blinked only when it detected light. How do we circumvent this error?

Thanks!

KenWittlief
01-13-2004, 09:45 PM
the banner sensors do not detect light - they send out a red laser spot that is modulated in frequency, and it looks for that specific beam to be reflected back - usually from retroreflective tape - but they will bounce of a white surface a few inches away. with retro-reflective tape you can see the tape up to 20 feet away!

if you are getting output overload errors on the sensors you have one of the outputs shorted. The banner sensors have 4 wires - one for +12V, one for Gnd (or negative) one that acts like a closed switch when the sensor sees the beam, and one that acts like a closed switch when it doenst

you should connect the gnd and one of the 'sense' wires to the digital input of the RC - and dont connect anything else to the sense wires. Make sure the unused sense wire is not shorted to ground or power

if you had 3 fail on you, I suspect you are connecting one of the outputs to gnd or +12V - we smoked one last year (they are expensive too!)

squide
01-14-2004, 02:02 AM
Thanks for the info! So we have 2 that are shorted, and we have one that works just fine. I looked up the price for them and they are about $60 each!

KenWittlief
01-14-2004, 09:24 AM
sometimes when the output is shorted the sensor still works. the led on the sensor will go on when it sees the retro-tape - so you could use it for demo purposed, but the output signal is dead so its no good for your bot.

PS - never throw any fried parts away - throw them on the dead pile, and at the end of the year glue them all together and make an award out of them for someone on your team.

squide
01-14-2004, 12:06 PM
Yeah, the sensors are still responsive which was pretty deceiving since we were trying to get them to work. The sensors are also good as necklaces/leis :D

Sparks333
02-03-2004, 08:59 PM
Hi!
Hey squide, the reason you have an overload is that the input for the sensor is 12vdc. Therefore, if you have it hooked up incorrectly, the signal will also be 12vdc when the switch is closed. That's really bad. the controller is only supposed to be getting 5vdc signal or 0vdc signal, but never 12vdc. The robot controller is pretty tough, so I do not think you will have fried it, but you will not get a consistent reading until you fix this. I have a schematic that I will be posting soon.

-Sparks333

seanwitte
02-03-2004, 09:18 PM
Hi!
Hey squide, the reason you have an overload is that the input for the sensor is 12vdc. Therefore, if you have it hooked up incorrectly, the signal will also be 12vdc when the switch is closed. That's really bad. the controller is only supposed to be getting 5vdc signal or 0vdc signal, but never 12vdc. The robot controller is pretty tough, so I do not think you will have fried it, but you will not get a consistent reading until you fix this. I have a schematic that I will be posting soon.
-Sparks333

The inputs are pulled up to 5 volts internally, so they're expecting to see either an open circuit or ground. The Banner sensors have an open collector output so its just like a switch. Its either open or grounded, there is no output voltage.

Sparks333
02-03-2004, 09:35 PM
Uh, yeah. I just now read that. Listen to him, he has all his homework done!!!

-Sparks333

wills
02-04-2004, 01:52 AM
Hey, a former FIRST employee here - now that I'm back in graduate school I read the forums here to satisfy my addiction.

I wrote this (for last year's EDU robots); it's a harness to up the voltage.
http://www.usfirst.org/robotics/primer/SensorHarness.pdf
I haven't looked at the new EDU robots, so check that this is still relavent