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rwaldron / galileo-io

Intel Galileo & Intel Edison IO Plugin for Johnny-Five
http://johnny-five.io
MIT License
101 stars 26 forks source link

PingFirmata on the Edison #55

Closed WoodyWoodsta closed 8 years ago

WoodyWoodsta commented 8 years ago

I see that no-one appears to have run into this issue wherever I search, so I may as well open an issue here!

I'd like to make use of the ping functionality for the HC-SR04 ultrasonic module on my Intel Edison (which is connected to the Arduino breakout), and I am not able to get the I2C backpack, so I understand that I need to have a custom firmata installed. However, there is no such version available for the Edison as far as I can see.

What exactly is required for there to be support for this functionality? The Johnny-Five site just states "hardware support missing" but I would like to know what hardware requirements this needs.

This is a fairly critical part that I need for my thesis and I'm willing to put some time into helping out getting this functionality up and riding, if the hardware allows.

reconbot commented 8 years ago

You're going to need an i2c backpack for the Edison to use an ultrasonic sensor that requires precisely timed pulses like the HC-SR04. Or you'll need a different sensor that has an analog out or i2c out on it itself. There's a huge list of parts that will work with the eidson on the proximity api page under "analog" and "i2c".

http://johnny-five.io/api/proximity/

To elaborate the Edison is't capable of precisely timing the pings and reads because all your code runs in userspace and can't make guarantees about when it will get the notice that a signal has been received.

WoodyWoodsta commented 8 years ago

After more reading, I understand that this is also due to Node's event loop and that watching a file change (the GPIO pin) in an "asynchronous" manner is still bound by the event loop reaching the point where it can fire a handler. What a pity, I will have to see what kind of accuracy I can get out of a pure js approach.

I still would not mind knowing why this cannot be rectified in the firmata. Unfortunately I'm not too clued up on how the protocol works!

reconbot commented 8 years ago

There is no firmata on the Edison. Even with c++ this is difficult or impossible to use achieve with sysfs. (File based gpio)

On Sat, Sep 17, 2016, 1:52 PM Sean Wood notifications@github.com wrote:

After more reading, I understand that this is also due to Node's event loop and that watching a file change (the GPIO pin) in an "asynchronous" manner is still bound by the event loop reaching the point where it can fire a handler. What a pity, I will have to see what kind of accuracy I can get out of a pure js approach.

I still would not mind knowing why this cannot be rectified in the firmata. Unfortunately I'm not too clued up on how the protocol works!

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WoodyWoodsta commented 8 years ago

Right! This makes a lot more sense to me now. Thanks for your help.