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Firmata test app

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(@pugwash)
Sorcerers' Apprentice
Joined: 5 years ago
Posts: 923
Topic starter  

After installing the "firmata_test.app" and running it, I discovered that the drop-down menus of all pins show a "servo" mode. I assume to drive a servo motor, perhaps I am wrong.

I have searched the internet for this servo mode without success, to find out exactly what the purpose is.

So I decided to throw my oscilloscope at the problem and this is what I found.

20000101 001918

 

Servo mode is pulsing for a maximum 2.34mS at approximately 50Hz. Adjusting the accompanying slider reduces the pulse time, but the frequency does not change!

Could anybody explain if

1. the servo mode is entirely independent of the Arduino hardware, i.e. a Firmata software mode?

2. what practical purpose could this possibly have to do with servo motors, if any?

 


   
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(@pugwash)
Sorcerers' Apprentice
Joined: 5 years ago
Posts: 923
Topic starter  

Now I am completely on my own here. The answer to question 1 is YES, it is software controlled but not by Firmata!

Judging by what I found in the servo.h library

#define MIN_PULSE_WIDTH 544 // the shortest pulse sent to a servo

#define MAX_PULSE_WIDTH 2400 // the longest pulse sent to a servo

#define DEFAULT_PULSE_WIDTH 1500 // default pulse width when servo is attached

#define REFRESH_INTERVAL 20000 // minimum time to refresh servos in microseconds

24oo microseconds was the maximum pulse width measured. And 1/0.02 gives 50Hz refresh interval.

Only question 2 yet to be answered!

I know, judging by that scan, the circuit could really use a capacitor.


   
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(@pugwash)
Sorcerers' Apprentice
Joined: 5 years ago
Posts: 923
Topic starter  

Bill,

I should have watched your youtube video before I started this! I am doing that now.

I have now got the answer to all of my questions and have my own slider control using Python/Tkinter that controls the angle of the dangle. Haven't hooked up a servo yet, just watching on the oscilloscope.


   
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Robo Pi
(@robo-pi)
Robotics Engineer
Joined: 5 years ago
Posts: 1669
 
Posted by: @pugwash

Bill,

I should have watched your youtube video before I started this!

It's always best to watch Doctor Bill's videos before trying to diagnose anything yourself.

If you think you have a problem
watch a DroneBot Workshop episode
it will save you much frustration
and your cranium won't explode

Servos like a frequency
of 50 hertz vibration
but no one knows why this is so
it's a freakish aberration

They thrive on getting pulses
to push them to and fro
and if you watch them closely
they'll give you vertigo

This poem has been brought to you
by a groggy Robo Pi
And no one in the universe
has an inkling as to why

 

DroneBot Workshop Robotics Engineer
James


   
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(@pugwash)
Sorcerers' Apprentice
Joined: 5 years ago
Posts: 923
Topic starter  

@robo-pi

It's always best to watch Doctor Bill's videos before trying to diagnose anything yourself.

I disagree, I believe you learn a lot more by making mistakes and finding your presumptions to be wrong, than being spoon fed with small palatable, easy to digest chunks! I prefer to fall back on the Grand Masters first when I have exhausted all my own possibilities.

I'd rather be a Sherlock than a Sheerluck! The journey being more satisfying than the arrival.


   
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(@pugwash)
Sorcerers' Apprentice
Joined: 5 years ago
Posts: 923
Topic starter  

This looks better, a 3.3 µF capacitor did the trick.

20000101 051458

   
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Robo Pi
(@robo-pi)
Robotics Engineer
Joined: 5 years ago
Posts: 1669
 

To each their own
a path through life
we wander through this world
Some just smelling flowers
whilst others are unfurled

The mysteries
they come and go
with the answers often fleeting
some content with education
while others see it cheating

Neither one is right or wrong
they're just being who they are
and in the end it matters not
cause life is so bizarre

DroneBot Workshop Robotics Engineer
James


   
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Robo Pi
(@robo-pi)
Robotics Engineer
Joined: 5 years ago
Posts: 1669
 
Posted by: @pugwash

This looks better, a 3.3 µF capacitor did the trick.

Nice fix on the noise. ? 

DroneBot Workshop Robotics Engineer
James


   
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(@pugwash)
Sorcerers' Apprentice
Joined: 5 years ago
Posts: 923
Topic starter  

@robo-pi

Although I come from Wales, I can neither sing nor am I good at poetry, but I thought I would share my favourite poem with you, one I had to learn at school many moons ago.

 

The Rising of Glyndwr

Thunder-browed and shaggy-throated

All the men were there,

And the women with the hair

That is the raven's and the rook's despair.

 

Winds awoke, and vixen-footed

Firelight prowled the glade;

The stars were hooded and the moon afraid

To vex the darkness with her yellow braid.

 

Then he spoke, and anger kindled

In each brooding eye;

Swords and spears accused the sky,

The woods resounded with a bitter cry.

 

Beasts gave tongue and barn-owls hooted,

Every branch grew loud

With the menace of that crowd,

That thronged the dark, huge as a thundercloud.

 


   
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Robo Pi
(@robo-pi)
Robotics Engineer
Joined: 5 years ago
Posts: 1669
 

I got into songwriting a few decades ago and I learned to jingle from that.  And now I can't stop. ? 

It's a disease from which I apparently cannot be cured.

DroneBot Workshop Robotics Engineer
James


   
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Spyder
(@spyder)
Member
Joined: 5 years ago
Posts: 846
 
Posted by: @robo-pi

It's a disease from which I apparently cannot be cured.

I thought you were talking about firmata


   
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Robo Pi
(@robo-pi)
Robotics Engineer
Joined: 5 years ago
Posts: 1669
 
Posted by: @spyder

I thought you were talking about firmata

I never use firmata
I choose to code instead
and I'll most likely be this way
until the day I'm dead

DroneBot Workshop Robotics Engineer
James


   
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