trouble with encoder obex...

kutalinelucas

I've been trying to use the "Quadrature encoder" method from the parallax obex (http://obex.parallax.com/objects/24/), but even though it is very well documented, I'm having difficulties getting it working and was wondering if somebody could see where I'm going wrong...

I have a faulhaber motor (micromo 1624...s) with a built in 2-channel magnetic encoder with 10 pulses/revolution.

All I'm looking to do at the moment is turn the motor untill the encoder returns a set amount of pulses, but I've been working so long now I can't see the wood for the trees...

VAR
  word Ratio
  long Stack[9]
  long Pos[2]                                     'create buffer for 1 encoders + delta
  long Encoder_count
OBJ
  Encoder : "Quadrature Encoder"
PUB Init
  Encoder.Start(11, 1, 0, @POS)
PUB Main
  Ratio := 18000
PUB Toggle  |   Time
  Time := cnt
repeat WHILE (Encoder_count < 50)                                        
  Encoder_count := POS[0]
  waitcnt(Time += 20000 - Ratio)
  OUTA[10]~~                                            'motor1
  waitcnt(Time += Ratio)
  OUTA[10]~                                             'motor2
 
Encoder.Stop
OUTA[10]~
RETURN

POS[0] doesn't seem to leave zero, and i've tried different encoders to no avail...

Any ideas would be brilliant

kutalinelucas

I've just noticed on the encoder data sheet that I have to put a transistor between the output and ground, so I think I'll have to order some bits to get it going...

StefanL38

How about just testing if the encoder delivers incrementing values?

Your program is still small but already includes a lot of variabilities which could cause the problem.

The main strategy for problem solving is narrowing down the areas where the problem could be.

So a first test-prg would only do

CON
  _clkmode = xtal1+pll16x
  _clkfreq = 80_000_000


VAR
  long Pos[2]                                     'create buffer for 1 encoders + delta
  long counter

OBJ
  fdx     : "FullDuplexSerialPlus"
  Encoder : "Quadrature Encoder"


PUB TestEncoder
  fdx.start(31,30,0,115200)
  Encoder.Start(11, 1, 0, @POS)

  counter := 0
  repeat
    fdx.dec(counter)
    fdx.tx(" ")
    fdx.dec(POS)
    fdx.tx(13)  'carriage return
    counter := counter + 1
    WaitCnt(ClkFreq / 2 + cnt)

Did you do something similar to check if the encoder-object delivers positions?

keep the questions coming
best regards

Stefan

kutalinelucas

hey Stefan. This is my first day with spin and my program is already considerably larger than I think i'm ready for...this is one of 5 objects in 3 cogs! to be honest that test code you posted is above my head at the moment, I have however tested the encoders by playing with the conditional statement...and the only one which seems to trigger is IF(pos[0] == 0). I was buggering around with this for a few hours then finally tracked down a data sheet for these motors/encoders (I bought them surplus). The document shows that there should be a bjt transistor between each channel and ground, and a 10k resistor leading to vss...which kind of makes sence as there way no voltage drop across the encoder channels when the motor was spinning. DC circuit theory isn't really my forte so I would never have guessed it. I've ordered some transistors so I'm hoping I will get better results once I've sorted the switching out. Thanks for getting back to me.

PJAllen

I've just noticed on the encoder data sheet that I have to put a transistor between the output and ground, so I think I'll have to order some bits to get it going...

I have some Faulhaber 16/3k minimotors. They have encoders, but they don't need external transistors.

kutalinelucas

ahhh...the data sheet I found is almost identical, just laid out a little different. So would I just pull the vcc to +5v; ground to common; and the 2 enocder outputs directly to consecutive prop pins? I thought vcc needed to be connected to the collector of a transistor...

I was buggering about with the prop program for quite sometime tonigh and i assumed the missing transistor was the problem because the motor PWM routine would only trigger if POS[0]== 0, so the encoder wasn't acatually switching...Either that or I'm not calling the method correctly

PJAllen

Right.
The/Their Vcc could go to 3V3, GND to Vss (Prop Gnd), and the ChannelA/Bs to Prop inputs.
The encoder outs are pulled up (de rigeur common emitter switches) so everything is in readiness.

If you run the motor slowly, you should be able to see the outputs change states with a voltmeter

kutalinelucas

Thanks...I'll give that a try now