Re: [nodejs] raspberry pi 2 B+ and node.js -- a drift and need a life perserver
On Aug 18, 2015, at 8:13 AM, jps birdzbeez wrote:
I am not a programmer and never claimed to be one.. I just read and read and
read.. trying to learn and understand.. but for some reason I am not sure I
am understanding how this works... if someone doesn't mind I need help to
point me in the correct direction to get my project going.. What I am able to
do is make it work in python but I like the idea of node.js over python..
The project is to use my raspberry pi to raise or lower a door (not a garage
door). At the top and bottom are Hall Effect sensors. Before raising the door
I want to verify the door is closed. If it is closed then raise the door till
it reaches the opendoor state. I have not had any luck with node.js
programming.. this is what I have come up with so far..
var gpio = require('rpi-gpio');
var doorclosed = 31; //hall effect sensor when door is closed
var dooropen = 33; //hall effect sensor when door is open
var opendoor = 35; //cause door to open
var closedoor = 37; //cause door to close
function raisedoor(callback) {
//verifydoorclosed(function verified door closed on gpio 31)
gpio.read(doorclosed, gpio.DIR_IN, readInput);
//if doorclosed is = true then opendoor till dooropen is true
if dooclosed = true
gpio.write(opendoor, 1, function(err){
gpio.read(dooropen, true, function(err){
gpio.write(opendoor, 0, function(err){
callback();
});
});
});
}
I don't mind reading if someone has a link that explains what I am missing..
thank you
You said the code doesn't work, but what actually happens when you run the code?
There's one typo, at least: dooclosed should be doorclosed.
if doorclosed = true isn't valid JavaScript. You would need to have
parentheses around the condition. Also, = is assignment; you want == which
is equality comparison: if (doorclosed == true)
I've never used GPIO before, but I took a look at the documentation:
https://www.npmjs.com/package/rpi-gpio
And what you've written doesn't seem to correspond to that API. For example, it
says you must use gpio.setup before reading or writing, and the code you've
shown doesn't do that.
The first time you call gpio.read, you're calling it as if it is a synchronous
function, but the documentation shows an asynchronous function (i.e. one that
takes a callback). It also only takes two parameters: a channel and a callback,
but you're passing three parameters.
In your other call to gpio.read, you're passing three parameters again, where
only two are expected, and the callback you're passing only has an error
parameter, whereas the API expects to provide the value that was read as the
second parameter in the callback.
Your code is also never checking or doing anything with the error parameter.
You always have to check if an error occurred, and if so, do something
appropriate.
Knowing, as I said, nothing about GPIO, I'm just guessing here, but as a
starting point, if you wanted to check if the door is closed, it seems like the
code would be:
function raisedoor(callback) {
gpio.setup(doorclosed, gpio.DIR_IN, function (err) {
if (err) return callback(err);
gpio.read(doorclosed, function (err, value) {
if (err) return callback(err);
if (value) {
// the door is closed
} else {
// the door is not closed
}
callback();
})
})
})
Probably the setup code should not actually be in the raisedoor function, but
instead in an initialization function you call once at the beginning of your
program.
You said you want to raise the door until it reaches opendoor state, but your
code doesn't contain any loops that would be necessary for implementing until
logic. Of course, you shouldn't actually write such loops in node since that
would block the event loop. Instead you'll probably need to check the sensor,
and if it is not yet the right value, use setTimeout to wait a number of
milliseconds and then check again. Or, better yet, it looks like the API sends
change events when a value has changed, so instead, you should listen for
that event.
The similarity of the names of your variables (dooropen, opendoor) is confusing.
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[nodejs] Re: raspberry pi 2 B+ and node.js -- a drift and need a life perserver
Your code doesn't seem correct (nevermind the syntax errors). You also
didn't post any potential results.
These kinds of questions would be better off at stackoverflow.com, but here
are a few pointers.
The thing to realize here is that gpio.read and gpio.write are async
functions, and your first call gpio.read(doorclosed, gpio.DIR_IN,
readInput); seems synchronous, so our check (if (doorclosed === true){} ) will
always fail.
You also seem to have too many params (according to documentation
at https://www.npmjs.com/package/rpi-gpio) at further gpio.read calls, you
only need PIN number and callback. The second thing is that your second
check (whether the door is closed) should most likely be polling, say,
every second or so, because this way it'll make a check right away after
starting the doorOpen, and it'll probably be too fast..
An example of a raiseDoor function would be as:
function raiseDoor() {
// first check that the door is closed.
// the callback we pass in is a function which will receive (err, value)
arguments - err if there was a problem during this call, value if not.
gpio.read(DOORCLOSED, doorClosedCallback);
}
Two things - I wrote the doorclosed in CAPS, to signal the developer (be it
yourself or somebody else) that the this variable is constant, we don't
plan to change it. I suggest doing this for gpio-pin numbers for code
clarity.
Second thing, now we need to write this doorClosedCallback. It will be
called when that gpio.read above reads the sensor value.
function doorClosedCallback (err, value) {
// check for errors
if (err) {
console.log('Error checking if the door was open', err);
return;
}
// if no errors, we can see the door position.
if (value === true) {
// door is open, skip.
console.log('Door open, ending.');
return;
} else {
// door is not open. We need to do two things:
// 1. kick off the door motor (write to 'opendoor' PIN)
// 2. start polling - check every second if the door is now closed, and
when it is, stop the door motor.
gpio.write(OPENDOOR, true, doorInMotion);
}
}
As you can see, I'm writing true, and again offloading this check of the
work complete to another function - that way it's easier to reason about
those simple functions with simplified jobs.
So let's write it:
function doorInMotion (err) {
// it will only receive an error if our gpio.write(OPENDOOR) failed -
meaning, if we failed to start the door motor.
if (err) {
console.log('Door start failed.', err);
return;
}
// now is the trick. We want to check every second if the door is open.
If yes, write a zero to opendoor pin, so that we stop the engine.
// we do this every second, and we save this interval.
var interval = setInterval(function() { // this inner function runs every
second, until somebody calls the interval.cancel();
// every second, check the door sensor.
gpio.read(DOOROPEN, function(err, value) {
if (err) {
console.log('Error reading door-open value.', err);
return; // also could be a good idea to stop the engine here,
because due to error, we don't know if the door is open or not, maybe
sensor has failed.
}
// anyway, if the sensor didn't fail, we can check the DOOROPEN pin
value:
if (value !== true) {
console.log('Door not yet open, keep the motor running.');
} else {
console.log('Door is finally open.');
// now stop the door
gpio.write(OPENDOOR, false, function(err) {
if (err) {console.log('Error stopping the door motor.', err);
});
}
});
}, 1000);
}
This is just one, basic solution example, it can probably be made better
and simpler. But I think it should at least get you started.
On Tuesday, August 18, 2015 at 5:49:40 PM UTC+2, jps birdzbeez wrote:
I am not a programmer and never claimed to be one.. I just read and read
and read.. trying to learn and understand.. but for some reason I am not
sure I am understanding how this works... if someone doesn't mind I need
help to point me in the correct direction to get my project going.. What I
am able to do is make it work in python but I like the idea of node.js over
python..
The project is to use my raspberry pi to raise or lower a door (not a
garage door). At the top and bottom are Hall Effect sensors. Before raising
the door I want to verify the door is closed. If it is closed then raise
the door till it reaches the opendoor state. I have not had any luck with
node.js programming.. this is what I have come up with so far..
var gpio = require('rpi-gpio');
var doorclosed = 31; //hall effect sensor when door is closed
var dooropen = 33; //hall effect sensor when door is open
var opendoor = 35; //cause door to open
var closedoor = 37; //cause door to close
function raisedoor(callback) {
//verifydoorclosed(function verified door closed on gpio 31)
gpio.read(doorclosed,
[nodejs] Does one call to http.get() pull all data chunks?
Hi all, I was doing the HTTP COLLECT tutorial that comes with Node.js. I originally had a loop to keep doing http.get() until it came back error or end, but later removed the loop and it still worked, which implied to me that one call to http.get() pulls *all* chunks of data from the URL. Does one call to http.get() pull all data chunks? Thanks, SteveT -- Job board: http://jobs.nodejs.org/ New group rules: https://gist.github.com/othiym23/9886289#file-moderation-policy-md Old group rules: https://github.com/joyent/node/wiki/Mailing-List-Posting-Guidelines --- You received this message because you are subscribed to the Google Groups nodejs group. To unsubscribe from this group and stop receiving emails from it, send an email to nodejs+unsubscr...@googlegroups.com. To post to this group, send email to nodejs@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/nodejs/c44a8186-6914-451e-96c7-e74260714a49%40googlegroups.com. For more options, visit https://groups.google.com/d/optout.
[nodejs] Re: raspberry pi 2 B+ and node.js -- a drift and need a life perserver
Forgot the interval.cancel():
On Wednesday, August 19, 2015 at 11:28:41 PM UTC+2, Zlatko wrote:
So let's write it:
function doorInMotion (err) {
// now is the trick. We want to check every second if the door is open.
If yes, write a zero to opendoor pin, so that we stop the engine.
// we do this every second, and we save this interval.
var interval = setInterval(function() { // this inner function runs
every second, until somebody calls the interval.cancel();
// every second, check the door sensor.
gpio.read(DOOROPEN, function(err, value) {
if (err) {
console.log('Error reading door-open value.', err);
return; // also could be a good idea to stop the engine here,
because due to error, we don't know if the door is open or not, maybe
sensor has failed.
}
// anyway, if the sensor didn't fail, we can check the DOOROPEN pin
value:
if (value !== true) {
console.log('Door not yet open, keep the motor running.');
} else {
console.log('Door is finally open.');
// now stop the door
And stop the interval here too: clearInterval(interval);
gpio.write(OPENDOOR, false, function(err) {
if (err) {console.log('Error stopping the door motor.', err);
});
}
});
}, 1000);
}
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