ping - ultra sonic range sensor(28015)-(filter)

tehmoordar

Hi,

is it possible that in the presense of motors the range sensor some times just gave erroneous data erratically. Like I use the term rollover to tell the distance is like 200 or 300 feet. I have tried to see the signal on oscope and there I see little noise continously on the screen alongwith pulses.
How can·I filter out these noises or how can I clean my signal. I need help in cleaning the signal.
Thanks

Doug Pientak

Hello,
The motor in your circuits is likely causing the noise.· To be sure look at the noise you mentioned and turn off the motor.··If the noise is gone when the motor is off then you know you are on the right track.·
To help with the noise from a motor I would need more specific details about how the motor is being driven.· Here are some things that might help:
-Isolate the motor driving circuit from the rest of your circuit.·
-If you have a wires going to the Ping))) (like the servo extensions)·be sure they don't go anywhere near the motors or motor driving circuits.· If needed use a shielded cable.
-Add Schottky diode to motor for back EMF. and add·some large capacitors.·
I hope this helps, let me know if you have any questions.·
Doug P.
Parallax Inc.
dpientak@parallax.com

tehmoordar

hi,
I am using board of education, on which is mounted the dual micro motor controller from pololu. Also is mounted the ping sensor.
I am using two power supplies one for basic stamp giving like 11v and other power supply for pololu dual micro controller and supplying 5v.
You ar eright if I turn of the motor then ping sensor works fine
I am already using capacitors 0.1 uf --- You want me to add Schottky diode -- what effect this will have on the motors or range sensor.
Let me use shielded cables for range sensor and motors and I will get back to you.
Thanks

tehmoordar

Hi,

I replaced the wires with shielded wires but my problem is not solved, Nows thats what is happening I am reading the signal from range sensor and encoder in Basic stamp editor and as well as in through DAQ card in my labview code as well.

Now range sensor works fine if only basic stamp is working and what so ever is the speed of motor but once I connect my labview which is connected through BNC connector 2120 of national nstruments· the range sensor starts blinking rapidly- if I slow down my motors then range sesnor works fine with both BS II editor aswell as NI labview.

I have held the motor in air just motor in air no circuit but simple 5V from power supply signal going to BS II and lab view as I increase the voltage the led blinking speeds up. take out the lab view signal wire then speed of motor has no effect and range sensor works fine.

Is this some ground loop thing going on -- like computer grounded, basic stamp grounded, motors grounded -- these making one big loop,

I tried to break the loop using 9 V battery instead of power supply for basic stamp and motors but it has no effect on the problem but but problem is the ground looping I feel-- what do you feel is my problem.

Thanks

Doug Pientak

Hello,

Can you draw me a schematic of how you have things connected? I can then explain how to install the schottky diode. Most speed controllers control the speed of a motor by PWM of some sort. When you turn a motor on and then off the motor creates back EMF (large noise spike). This noise spike is what is causing the Ping to act wired. The diode will force this noise back into the motor. You need a schottky diode to handle the fast speed of the noise.

If all you have is .1uF capacitor you need to increase that to a 100uF or even 300uF if you have them (larger the better). You may need to put capacitor in a few locations, ie. large cap at the motor driver, large cap at the stamp and digital electronics. These caps should be connector to the power for that circuit and physically very close (no more then .5").

Try the caps out first that may fix your problem. I don't think you have a ground loop but I can tell more when I see a schematic.

Hope this helps,
Doug

tehmoordar

HI,
I am sending you my schematic layout. Iam using pololu dual micro motor controller (www.pololu.com), it can·handle upto·2 motors upto 2amps. My motors consume more than 2 amps so I am giving them very less voltage 3V that is 3V at the motor controller motor supply from my power supply#2 but motor controller logic supply is coming from basic stamp which is connected to power supply#1. Now then two motors are connected on four terminals at motor controller. this motor controller works on the PWM principal. My motors are DC motors (www.hobbyengineering.com· item# 1205)

Now sensor has three legs(+5V, gnd, signal out) power is being supplied by basic stamp and signal is· going into input/output of the basic stamp II. The same signal is going into BNC connector as well to see it in labview too.

Now basic stamp is also connected to computer and BNC connecter is also connected to computer(daq card inside computer)

Now computer and 2 power supplies are connected to power socket in wall.


Thanks

tehmoordar

Hi
I have used the capacitors, I am using the shielded wires but still the moment I switch motors on I can see the behaviour of range sensor changes. I can see Rf creating trouble for range sensor
I need to put diode as you suggested but how?
thanks