Home made optical rencoder issues

[Bill Legge]

I spent quite some time fiddling with home made units - got them working in the end:

1. Whilst the disks may have nice sharp/defined edges, the light source and detector probably occupy some 'area' and are not 'points.' so the interrupt is not a clean ON/OFF?

2. In one application I used the MC14490 de-bounce chip (Cost about $3 with 4 channels with internal pull-ups) and my problems went away - application was a tipping bucket rain gauge.

3. In my home made motor feedback project I had to 'sharpen-up' the pulses by using a 74LS14N Hex inverter Schmitt chip. The OSMC DC motor driver sprang into life and I had proper closed loop speed/position control.

4. Can you used some square wave source to emulate the interrupter to find out if it's dirty pulses or a frequency problem?

I've not used any software de-bounce but presume its fine as long as the delay is acceptable and info is not lost?

Good luck - let me know how you get on.

Gerards Bill Legge

[Elnino]

Thanks for the reply Bill, It looks like this might be more of a problem than i anticipated. I tried putting the disks closer to the photo transistor in hope that it might produce a squarer signal but that did not work.

supplying a square wave to the chip works fine. Even manually pulling the pin low with a mechanical switch does not produce unwanted pulses!

I might also try increasing the value of the pullup resistor so that it is much easier for the transistor to pull the pin low. I read on here someone using the sensors from an old ball mouse had to go in the order of 10m to get to pull low at all. These sensors are more sensitive/powerful but it might help reduce the issue of non-saturation of the transistor on the edge of a trigger point.

If all else fails i'll have to look at one of the chips you mentioned. I don't really want to go adding debouncing to the code and miss pulses at higher rpm.

Thanks for the input!

Andrew

[mackrackit]

Does the black portion of the disk completely cover the receiver and then some?
Use a very small clear opening and a wide dark for slow apps, also works for high speeds too.

[aratti]

Without the chopper disks, if i break the beam on the sensor with something opaque, i get an increment of 1 on the counter and same when the beam returns to unbroken. This works as expected. If the sensors are left alone, i do not get any increment. With the encoder disks in place i can rotate them at pace and get believable increments. My encoders are ~50 pulse/rev and i can get about 50 pulses if i manually rotate it about 360 degrees.
My problem is when i rotate them slowly - i.e just a small movement might increment the counter by 10 or 20. My assumption is that the sensor is on the edge of the opaque bit on the encoder and 'flaps' a bit. But, i do not get this when i manually break the beam which seems odd.

That simply means that your disk is not sufficiently opaque. Tray with two disks one on top the other (even three if you have room), this will increase the opacity by a factor of 2 or 3.

Al.

[Elnino]

thanks for the input people, i really appreciate it.

I am going to try printing them on another printer first. The other one i have is a Xerox which has the ability to 'pile on' the toner and make it really thick. The other hp laser i have is a little on the pathetic 'economy' side.

The awkward thing is, the data sheet does not really give specifics on the working area of the sensor, only where the optical center of it is. i.e it does not tell me the minimum width over the optical center to sufficiently break the beam.

I think i should be able to get it to work without any extra electrics or de-bouncing but it might take a bit more trial and error. I don't think its a debouncing issue as it does not bounce when i break the beam with something random - even a piece of torn off paper seems to be fine... It mush just be my dodgy disks.

[boroko]

I remember reading somewhere that someone was having similar problems with printed disks. The issue was that since the detection was IR, the visible black was not being seen by the sensor. You might try something else for those detectors as a test, say stripes of black tape.

Just a thought.

Bo

[Acetronics2]

Hi,

Did you had a look to Parallax kit of 44 " stripes " wheel encoders ???

http://www.active-robots.com/product...lwatcher.shtml

look same as you try to do ...

Already working.

my two cents...

Alain