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magnetic rotary encoder problem

Posted by Dylan 
magnetic rotary encoder problem
December 30, 2008 12:44AM
I am only hooking it up to 5v power and gnd.
I get the Ined, quadA, quadB LEDs to light up just by powering it, none of the LEDs change when the magnet is in place or turning.
I'm sure I got it soldered correctly, I even took my webcam and zoomed in on my large tv to see it, plus used a voltmeter to check connection from the led solder to the actual pin on the chip and it shows a solid connection.
any ideas?
Re: magnetic rotary encoder problem
December 30, 2008 02:29PM
Check for shorts between adjacent pins, by measuring the resistance between adjacent pin circuits over at the pads on the other components connected to the pins in question. Also, if you have a camera, take a macro photo and post it, I might be able to check your part placement for you.

Re: magnetic rotary encoder problem
January 05, 2009 12:23PM
here are a few photos from my webcam. I have a high res scan link lower down.

Click here for a really high res scan of it.

I tested them with the voltmeter and there aren't any shorts. When I test pin 7 (gnd, with quada, b,, or index, the LEDs light up a little, but I would assume that's normal because of the power the meter sends through the circuit.
Re: magnetic rotary encoder problem
January 05, 2009 01:03PM
Wow, that's one hell of a webcam! The really high res scan photo did the trick - I can see your problem.

The MAG+, MAG-, PWM led's are on backwards. The silkscreen is a little non-obvious, but you can see it in the photos on the build page - those three LED should have the green colored side of the LED reversed relative to the QUADA, QUADB and INDEX led's. That chip looks like it's soldered on fine.

It's a little fiddly getting the magnet exactly right, and it won't pulse the quad outputs until it's just right, and you need the Mag lights to do that. My magnet has to be about halfway inside the hole in the PCB.

Hope that helps!

Re: magnetic rotary encoder problem
January 11, 2009 12:40AM
ok, thanks, I see it now. I tried getting them off, but it looks like I broke them. I need more of these chips for another project anyway so I'll try to get a few extra from Zach. I am a little concerned that the other 3 LEDs light up with just power connected. I thought the index was only supposed to flash on once per rotation not be on all the time. Could this be a problem with having the other LEDs backward? If someone can test their board with just the 5v power and tell me, that'd help.
My webcam is actually my playstation 2 camera held an inch away from the board and focused properly. It worked well though.
I really need to get some flux for this kind of thing, the soldering on it was a real pain.
I'm still waiting for a pwm setup on the site, but don't see one yet.

thanks for the help. hopefully this board will work once fixed. you think I can put other LEDs on instead?
Re: magnetic rotary encoder problem
January 11, 2009 01:24AM
Nuts, I was going to say something about desoldering SMD parts, but guess it's too late now. The easy way is to use two soldering irons, but you can do it with one if you pile tons of solder on both contacts of the LED, and then pass the iron back and forth until you get both pads melted simultaneously. Or try to angle it so that you're touching the solder on both pads with the iron at the same time. Either way it's messy, and you have to clean up with solder-wick afterwards, and the LED's may or may not survive. A heat gun will do it too, but I don't like to use them, they tend to desolder the entire board for me.

You can also order more LEDs from Digikey, just look up the part #; they ship overnight to the US and Canada. We used to joke that we could get parts from Digikey faster than we could find them in our own store room downstairs.

Having the other LED's backwards shouldn't change anything. I think the chip lights up both MAG+ and MAG- when the magnet is too close or too far, so that's probably what you're seeing, assuming the chip hasn't been zapped. It should actually work fine without all the blinkenlighten, you could hook the PWM output up to a scope or an Arduino and see if you're getting anything out when you spin the magnet.

Re: magnetic rotary encoder problem
January 11, 2009 09:03PM
It wasn't the mags I saw light up, it was the quads. Although I thing I fried my chip. I got the LEDs off and the second one works still, but the first one is dead. I replaced it will a small through hole and that lights up, but to test it, I kinda forgot about my voltage converter for 5v and had it connected directly to 16v... damn. when I first did this, the 3 quad and index lit up then turned off and went to the mags. I kicked myself and then swapped the voltage and now the mags are lit no matter where the magnet is in relation to it. I tried the hole, I tried on top of the chip, as close and as far as possible and everything in between.
Apparently Zach is out of these at the moment too.sad smiley
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