Skip to main content

setting up pwm

There's always an obstacle..

I implemented the pwm module as described in the link in the previous post, but oddly enough, it didn't work.

The error I received:

AttributeError: 'module' object has no attribute 'PWM'

After some time scratching my head, I came to the realization that somehow my python was running an older version of the RPi.GPIO library, as PWM control was a pretty recent addition to the library. 

And indeed it was. 

Not really sure what's happening in detail, but it seems that there are two different... entities? that manage libraries for Python. One is through the usual "apt-get" command and the other is "pip." It appears that Python looks at "pip" first, and it currently linked RPi.GPIO to a really old version of the library. 

Uninstalling that older version ("pip uninstall RPi.GPIO") and using the version I obtained through apt-get ("apt-get install python-rpi.gpio") solved this. 

Now, a less-hacky implementation of PWM. 

Note that the PWM offered in this library is a software-driven PWM, meaning that the cycles it counts are based on the cycle count of the process (program). This can be inaccurate because programs can be put "on hold" by the operating system during heavy load, and during this time on hold, it stops counting. Because PWM relies on timing, this could cause "jitters" in the devices that read the signal. A better implementation is a hardware-driven PWM, which uses the clock cycles in the physical board to count. 

For now, I think the software-driven PWM will be fine.

Time's up for working on this today; I'll change messages into JSON next time, I guess.
Labels:

Comments

Post a Comment

Popular posts from this blog

finally got around to it (nrf24l0+ and servo)

On a previous post , I used the nrf24l01+ wireless chip to communicate between the Raspberry Pi and an Arduino, but only got lights to turn on. I remember being confused as to why servos would not work, and somewhat left it there. I started messing around with it again, and I am concluding that it might have been just a power issue. Here is the servo moving properly: The Arduino is on the ground due to the short length of the wires powering them. Just as a recap, what is happening is: - a C++ program using the RF24 library is compiled in the Raspberry Pi (connected to an nrf24l01+ chip) to broadcast a message. When executed, it will broadcast the message. - the Arduino (connected to another nrf24l01+ chip) programmed to receive messages receives the message, and upon receipt sends a signal to an Arduino that is wired to the servo to move the servo. Two separate Arduinos are used, as it seems that the servo library and the RF24 library do not seem to run properly toget...
Post a Comment
Read more

alcohol sensor (and some patience)

Soldered the alcohol sensor into something that is connectable: I tried to connect this to the Arduino, as I had the appropriate circuitry, but I did not get any legitimate output from it. 5V going in, 5V coming out with no variations. Nothing seems to be awry in wiring, as the circuit seems to be grounded properly (and the 5V current is flowing).  There are a couple of potential factors as to why I'm not seeing any results: - I'm using a 10k ohm resistor, while some guides (and the datasheet for the sensor) asks for 100-200k. However, there seems to be a good amount of people using 10k and getting at least some kind of result. A batch of 100k ohm resistors I ordered is on its way, so I guess I can try with them when they come. - This site  claims that these sensors take 24-48 hours for its signals to be stable. It also tells me that I should not be powering the sensor directly from the Arduino, which I have been doing, out of concern that the power draw of ...
Post a Comment
Read more

how the fingers work

the fingers are moved using wires and tension. each finger is looped through with a wire/string/line in a top-bottom fashion. when the top wire is loosened/bottom wire is tightened, the finger curls in its joints, resulting in a "bent finger".  you don't have precise control of each joint movement, but it is simple enough to be controlled by a single actuator (in this case a servo).  here is me just using my own hands as an actuator: here it is hooked up to as servo and controlled by a potentiometer: the movement is not smooth because 1) it's controlled by a potentiometer that I am controlling, as seen in the background, and I was unable to move it all the way with one smooth finer motion. 2) the tension in the line was not entirely tight. I need to learn how to tie these well. now I have a get a bunch of servos.  much credit and thanks to Inmoov once again.
Post a Comment
Read more