Optical Encoder Part help - Page 1
Forum section: electronics / beginners

author: Izrun
author_rank: Newbie
timestamp: November 13, 2013, 03:05:38 pm
content: Hello All,I am at a complete loss and I could really use some guidance. This should really be an easy question. I am trying to build a quadrature encoder like there are in a billion ball mice. In those devices they usually have a single IR detector that has two channels so you can detect direction of rotation. I can't seem to find these two channel, single part devices ANYWHERE. I am so frustrated because I'm sure the part should cost next to nothing. The only device I have found with this functionality is this (http://tinyurl.com/lhjyw82) which honestly isn't a bad option, but there must be more choices. I don't care if it is an all-in-one device like the one linked or just the detector. Any help would be greatly appreciated. Thanks!

author: jeroen74
author_rank: Frequent Contributor
timestamp: November 13, 2013, 03:56:23 pm
content: Likethis?

author: Izrun
author_rank: Newbie
timestamp: November 13, 2013, 04:14:01 pm
content: Thanks for looking into this. Technically yes, that is right. I guess I should have been more specific though. That is one of those high resolution modules that cost ~13 bucks each. I'm looking more like old school mouse ones which are significantly cheaper. I've torn some apart and they are just a little rectangular receptor that from the look of it would be <<$1.

author: codeboy2k
author_rank: Super Contributor
timestamp: November 13, 2013, 06:07:20 pm
content: Do you have a picture of what you are talking about?because the old school mice that I know about have exactly what you linked in your original post.. and they have 2 of these, one for X and one for Y, with large slotted black disks that pass through the gap. And then it can ascertain each of up/down in the Y direction and left/right in the X direction.The image below actually has separate IR transmitter (white) and receivers (black).The other technology used was Logitech's trackball system, which used a spot patterned ball and a just two IR transmitter/receiver pairs.Later mice went to an optical image array that detected changes in direction by comparing previous images to newer images.So I am not sure what you are looking for, because your original link and the link provided by jeroen74 seems like the right thing.Are you looking for a hall effect sensor? these can detect magnetic fields moving in and moving out, but I don't know if any mouse ever used a hall effect sensor.

author: jeroen74
author_rank: Frequent Contributor
timestamp: November 13, 2013, 06:51:49 pm
content: Thisone then? (which showed up as an alternative on the page linked to in the opening post...)One led, two receptors, all in one housing for little money....

author: Izrun
author_rank: Newbie
timestamp: November 13, 2013, 08:30:11 pm
content: Thanks guys. I guess I was just paranoid building a design with only one option. I figured I was missing some huge class of devices. I guess the device I first showed is what is in a mouse, just in a nice little package instead of raw components. I need to work on my confidence. This is my first design since college 12 years ago.

author: codeboy2k
author_rank: Super Contributor
timestamp: November 14, 2013, 12:22:11 am
content: You're welcome.. You can always try to roll you're own with a separate LED and detector, like in that mouse picture I posted.There are many, many ways to optically encode, and these go from the simplest and cheapest LED and Detector (which are transmissive detectors, i.e. they chop a transmitted light), reflective: has the transmitter and receiver above the plane of reflection, which is usually a white/black coded disk, this can give higher resolution. A more expensive approach can involve rows of detectors, and even up to video camera type matrix ccd detectors.and you can encode linearly too. Good for tracked mobile platforms.So spill your beans now.. what are you building

author: Stonent
author_rank: Super Contributor
timestamp: November 14, 2013, 12:45:33 am
content: Quote from: codeboy2k on November 14, 2013, 12:22:11 amEven 2 LEDs can be used as a transmitter and receiver.http://en.wikipedia.org/wiki/Forrest_MimsScroll to the section on using LEDs as narrow band light sensors.

author: Izrun
author_rank: Newbie
timestamp: November 14, 2013, 12:56:34 am
content: You know, the roll your own detector was really my first choice, and kind of what initiated this request, but I could not find dual channel detectors anywhere.You're right that there are so many ways to so this. I really don't know what the bet choice is either. Maybe you might have a better idea.The final product of this will hopefully be a consumer-ish product. Not expecting to sell tons, but trying to make it low cost. What I'm trying I do with this portion of it is basically this. I have a tiny geared motor (for the prototype I'm using the pololu motor with extended shafthttp://www.pololu.com/product/2204) and the encoder module that they sell. The encoder is a reflective one that sits on the back of the motor. My goal for this portion is to basically turn the motor into a servo, where you would say I want to turn it X degrees one way or another. The shaft should also be able to be turned by hand and the device needs to know how many degrees it turned. If you know the gear ratio and you know how much the littlemotor has turned using the extended saft you can figure out how many degrees you have turned. It doesn't have to be perfect, so I think this should work well enough.The whole thing had to be less than an inch wide and can be a little long, but as compact as possible. So to do this in a production environment, I figured it would be a lot more expensive and complicated to have one board on the back of the motor and and a longer one perpendicular to it. I thought I could use this kind of encoder disc and be able to have all my chips and stuff on one board. I thought about Hall effect sensors too, which I might also be trying.I hope this makes sense. I tend to ramble and I'm typing this on my phone