View Full Version : Looking for others with experience using micro switches as wheel encoders for t

Russ Ferguson
10-21-2004, 12:59 AM
I recently purchased the "Boe-Bot Digital Encoder Kit" and am very pleased with it.

It appears to me that a micro switch would come close to providing the same feed-back as the optical interupter. Does anyone have articles on using micro switches as wheel encoders with the new Boe-Bot wheels?

I purchased a set of micro switches·to start experimenting with and will share what I learn.

10-21-2004, 01:56 AM
The big difference between Encoder's and a micro-switch is switch-bounce.
The Encoder's will have no bounce. The micro-switch will 'bounce' for a
few milliseconds.

When you're trying to read the edges of the encoder signal, to know when
your wheel has turned a certain amount, debouncing the micro-switch
becomes a pain. It may even limit the maximum speed you can go,
if you are going to keep up with tracking the wheel position.

Just a thought.

Russ Ferguson
10-21-2004, 03:40 AM
The code that came with the "Boe-Bot Digital Encoder Kit" only looks to see it the state has changed since the last status check. The code does not watch for the instant that the state changes.

I am going to assume that a simple RC debounce circuit will make the status clean enough.

Thanks for bringing this up.

10-21-2004, 03:58 AM
Sure. I don't know how repeatable the mechanical switch-point will be. If it moves around a lot, it may throw off your wheel movement measurement. Otherwise, why not give it a shot?

Russ Ferguson
10-21-2004, 09:27 PM
The wheel does have alot of play in and out. It is probably not a good idea to try to run the switch arm directly on the side of the wheel, perpendicular to it.

I quess that I am going to look for some type of a cam to fasten to the inside of the wheel. The cam action will be on the edge and not on the side.

Chris Savage
10-21-2004, 11:55 PM
To elaborate on Allan's comparison, the Parallax Encoder is optical, and therefore not subject to "wear."· The Micro-Switches are mechanical, and thus have a "MTBF" rating for contact lifetime.· Depending on how often the switches are closed (Which will affect resolution), the switches could wear out pretty quickly.· I'm sure Tracy Allan could do the math!· http://forums.parallax.com/images/smilies/tongue.gif

Chris Savage

Knight Designs
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