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51
Electronics / 50$ robot - Led supposed to light up??
« Last post by washb0ard on July 16, 2014, 05:31:23 PM »
Hello all,

 I see the below piece of code in the photovore_v1.c.. And based on how the Led is wired up in the pcb. I am confused whether it is supposed to glow when LED_off is called, can someone please explain?

 I feel that when LED_on is called a digital is in output on the pin DP4 which is connected to the negative of LED and the positive of LED is connected to 5V(Vcc). Since there is no potential difference iam not sure if it supposed to glow

Code:
        configure_ports(); // configure which ports are analog, digital, etc.
   
   a2dInit(); // initialize analog to digital converter (ADC)
   a2dSetPrescaler(ADC_PRESCALE_DIV32); // configure ADC scaling
   a2dSetReference(ADC_REFERENCE_AVCC); // configure ADC reference voltage

   /*********ADD YOUR CODE BELOW THIS LINE **********/
   delay_cycles(500);//a small delay to prevent crazy oscillations
   LED_off();//turn LED on

52
Software / Re: Problems uploading to Axon II using McUber
« Last post by Hero I on July 15, 2014, 03:48:25 PM »
Did you install the USB drivers, and does your PC properly recognize that the Axon is plugged in?

Yes and yes.
53
Mechanics and Construction / Re: bandwidth of two wheel inverted pendulum
« Last post by Billy on July 14, 2014, 11:09:12 PM »
As for using a physical filter at the output of the accelerometer, I would suggest going with a digital filter instead, such as an IIR.

He/she needs an anti-aliasing filter. That is always physical. The IIR or FIR can be used for tuning.

Everything else you said was spot-on!
Late to conversation. My apologies.
54
Electronics / Re: Servo Problems
« Last post by Billy on July 14, 2014, 10:59:12 PM »
what do you mean by  isolation or the servo pulses being irregular(do you mean the servos might be the problem)?


Isolation is a means to leave two circuits unconnected electrically, but allow for information (signals) to pass from one circuit to another. There are several types but include using light to send signals in an optocoupler (optoisolator), or to use magnetic field in a signal transformer or digital isolator. I have even seen a large 50 Hz 3 phase power source isolated from the 60 Hz 3 phase power supply by using a large motor to turn a large generator. In that case the signal was mechanically transmitted.
Here is a link you should have read prior to posting your question, but I'll you slide by on this one: http://en.wikipedia.org/wiki/Galvanic_isolation
It's not the best wiki page I have seen but least they took the time to include diagrams.

Your cell phone allows your parents to send a text saying to come home without you having to actually see your parents, so that would be called social isolator.  Angry mom or happy mom, all you see is the words sent by mom. You don't see the upset look on her face because you're late for dinner AGAIN! You only get the clear, quiet, no-attitude message to come home.  Same with electrical isolation; you get the signal without the electrical noise that is on the other circuit. Angry circuit or happy circuit, you only get the message sent.  Motor (servo) circuits can be noisy (angry) and that noise interferes with the communication between uCs (mom) and other electrical parts (you).

My comment on the pulses being irregular meant simply that the pulses from the uC may not be the same distance apart or not the correct width every time the uC sends one. Maybe your SW is thinking about something else when it should be thinking about sending pulses.

I don't know anything about Ardinos so do not know how the pulse trains are generated. If they are generated by flipping bits in an interrupt routine then maybe you're taking too long in the interrupt and missing the start of the next scheduled call, or maybe you're modifying a variable that gets used in the interrupt when the interrupt gets called, so it's not the value you want it to be. Can't help you there.
55
Electronics / Re: Servo Problems
« Last post by vipulan12 on July 13, 2014, 05:22:44 PM »
Thanks for the advice, I ll try that and see what happens
what do you mean by  isolation or the servo pulses being irregular(do you mean the servos might be the problem)?
56
Electronics / Re: Replacing two analog POTs in mobility scooter bot
« Last post by tgibbons on July 13, 2014, 04:24:56 PM »
Thanks for the feedback on the voltages. That had not occurred to me. You were correct that 2.5v on the main control circuit was stop and 0v was full reverse and +5v was full forward.

Since this was a control voltage, I was able to control it with a PWM output from an Ardunio Uno. I was happy to find a digital PWM output would work for this, so I was able to replace both pots with the digital output from the Ardunio. 

Now on to replacing the mechanical steering...
57
Electronics / Re: Servo Problems
« Last post by Billy on July 13, 2014, 02:39:33 PM »
i first tried grounding everything together, that worked but the twitching came back
i also tried changing the batteries which also worked for a little while but the twitching returned


In every system where there are issues that can be attributed to noise, one of your first actions should be to stabilize the supply. Think of the batteries as the power source for your power supply. The power supply at each part being bypassing capacitors.
http://en.wikipedia.org/wiki/Decoupling_capacitor
On each of your power lines, and including at the battery, try install a 10uF electrolytic cap in parallel with a 1uF ceramic cap. Install these at the batteries, and if possible at the power connectors to the servos.

You said you power the uC from a 9 volt battery. That is OK but the negative terminal of the 9V battery must be connected to the negative end of the AA battery pack. That assumes you do not have any isolation between the servo circuit and the uC. Isolation is an advanced topic that you should consider if you still have issues.

Final thought: your description makes it sound like a noise issue, but of course it's possible you have a SW issue and the pulses to the servos are simply irregular.
58
Software / real time operating system
« Last post by ansh on July 13, 2014, 08:26:04 AM »
    
I am not really going to design I just want to learn something before design
I want to design my real time operating system , so I need features , requirement component and tool

I need to develop program For real time operating system
my effort
1)basic tool
compiler
linker
debugger

2)language
c language

3)requirement
requirement of real time os should be fast

features
kernel - micro kernel
scheduler - real time scheduler
multitasking - multitasking
scheduling - preemptive scheduling


I think I have forgotten some features
59
Electronics / Servo Problems
« Last post by vipulan12 on July 12, 2014, 06:19:05 PM »
hey guys, I was working on a biped robot that uses the UNO and 10 servos, and by changing the angles i should be able to make the robot walk however for some reason my servos tend to twitch like crazy
i am powering the 10 servos using 8 AA batteries(6 volts in parallel) the arduino is not powering any of the servos
the arduino is being powered by a nine volt battery (seperately)

i first tried grounding everything together, that worked but the twitching came back
i also tried changing the batteries which also worked for a little while but the twitching returned

a friend said that I should power the servos using the batteries and the arduino in parallel(could this potentially damage my arduino?)

what exactly is the cause of these twitches?
they mainly occur at  the moment the servos are powered(just by flipping the switch pn the battery pack)
60
Electronics / Re: Odometry "like" an Optical Mouse
« Last post by bdeuell on July 11, 2014, 05:58:15 PM »
I had to look up how an optical mouse works ... (http://computer.howstuffworks.com/question631.htm) but it seems to me like you could build a scaled up version with a light and camera. The challenge seems to be in the software to process the images ... and i'm not much help there. However if my understanding is correct I don't see why it couldn't track orientation as well. My thought is the software would compare two images and find the transformation that provides the best fit. The best fit would look for a transformation that would include translation in x and y as well as rotation about the z-axis. Of course adding another degree of freedom (rotation about the Z-axis) to the transformation increases the processing required.

I am looking at a sensor for a project at work that detects translational motion using Laser Doppler Velocimetry. There is a version that can detect both x and y translation but not rotation. I would think you could use two sensors a fixed distance apart and calculate the rotation from the difference in the two sensor movements. However these sensors run about 10k for a single axis detection capability so they are probably outside of your price range.

... just some thoughts on the problem, probably not very helpful.

If you do find any sensors capable of measuring the translational movement of an irregular surface without contact (even if it is only in one axis) I would be interested.
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