Digital Encoder Interfacing

blittled

I'm setting up a Boe-Bot with a protoboard and was wondering if there was an object that interfaces with the Boe-Bot Digital Encoder. If not, is there a way to use CTRA/CTRB to count both the positive and negative edges of a pulse? That way I can get 16 counts per revolution. Thanks!

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MagIO2

I don't know the specs of the Boe-Bot encoders, but shouldn't this driver do the job?

http://obex.parallax.com/objects/24/

Besides that -·how would counting the edges work?
First of all you have as many positive edges as negative edges (plus/minus 1) by nature of digital signals. But what about the direction? That's where counters can't help you i guess. You really have to analyse the signals for detecting the direction the encoder has been turned in.
I think there exist at least two types of encoders. The one type I found in a mouse I dissassembled (the mouse wheel) gives two signals where both change within one step but with a little timeshift. The encoder I bougth only changes one signal with one step. But for both the signal sequence·looks the same:

turn in one direction                      turn in the other direction
00                                         00
01                                         10
11                                         11
10                                         01
00                                         00

Post Edited (MagIO2) : 6/29/2009 12:22:29 PM GMT

agfa

you could use two counters per wheel and set one to count pos edges and another to count neg edges and total them. you could also create a simple routine in spin ,or PASM if speed is an issue, to do the same with out the counters. if your refering to these encoders http://www.parallax.com/StoreSearchResults/tabid/768/txtSearch/encoders/List/0/SortField/4/ProductID/80/Default.aspx i don't think they have a quadrature output.· determining direction wouldn't be needed since the direction you are driving the wheels is known.

agfa

MagIO2

That's what wikipedia says about the boe-bot device:
"Rotary sensors with a single output are not encoders and cannot sense direction, but can sense RPM. They are thus called tachometer sensors."
And that's how I understood the word encoder. Ok ... boe-bot is only using a tacho and that can be done by a counter of course. At least one for the right wheel and one for the left. Counting positive AND negative edges increases accuracy. You can have a look at the Propeller App Notes AN001 - it shows how to set up the counters for edge count. Find it in the download section or the sticky.

blittled

Thanks for all your input. MagIO2, you are right they are tachometers and I already know the direction of rotation. I read ANN-001 and it mentions that the counters can count on negative or positive going edges but not on both. Since the tachometers moves slow enough a simple spin program that checks the state of each tach and increment a variable when there is a change of state should work. I just thought there may be an object since I saw a thread mention a rotary encoder object but I couldn't find it in obex.

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
What electronics need - MORE POWER!!!!!!!