April Maker Challenge!!!!

Topics generally related to Twin Cities Maker activities
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Nicholas Lee
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Re: April Maker Challenge!!!!

Postby Nicholas Lee » Fri Apr 10, 2009 9:00 pm

yeah. i think modifications count - as long as it is COOL ENOUGH.

just got cracking on some image stuff via processing.
holy crap. this will take a while... i might be happier (read: saner) breaking that project down a bit.
there is an explanation as to why vision systems are a non-trivial task: Edge-detection being one of them.

anyone have ideas on how to EASILY map two discreet balls (for example - two dark solid circles on a white sheet of paper) via processing and a webcam?

uptownmaker
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Re: April Maker Challenge!!!!

Postby uptownmaker » Fri Apr 10, 2009 9:36 pm

jtbarclay wrote:Are improvements to previous projects allowed? I hope so cause I already did the case for my crazy fan, and now I'm about to add one or maybe 2 1F 5.5v caps to yesterdays picaxe controlled zipzap car.

If I figure out what the current draw is at full speed, is there a way to calculate how long this thing will run on a fully charged 1f cap? Full speed is also way too fast for what I want to do with it anyways, so if I pwm control the speed I'm guessing the run time should increase?


A one farad capacitor charged to one volt will contain one coulomb of charge. 5.5V = 5.5C each.

Yes, using PWM to chop the draw WILL grant you longer life. If you REALLY want to go nuts, try using PWM that increases the pulse width to maintain a steady power delivery rate as the voltage drops off due to the cap discharging.

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jtbarclay
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Re: April Maker Challenge!!!!

Postby jtbarclay » Fri Apr 10, 2009 9:52 pm

Sadly the charger for the internal battery is only getting the cap up to 2.7v

And my pwm function is kinda limited

Code: Select all

pwm
Syntax:
PWM  pin,duty,cycles
- Pin is a variable/constant (1-4) which specifies the i/o pin to use.
- Duty is a variable/constant (0-255) which specifies analog level.
- Cycles is a variable/constant (0-255) which specifies number of cycles.  Each cycle takes about 5ms.

Function:
Output pwm then return pin to input.

Information:
This command is rarely used. For pwm control of motors etc. the pwmout command is recommended instead. This pwm command is used to provide ‘bursts’ of PWM output to generate a pseudo analogue output on the PICAXE-08/08M (pins 1, 2, 4). This is achieved with a resistor connected to a capacitor connected to ground; the resistor- capacitor junction being the analog output. PWM should be executed periodically to update/refresh the analog voltage.

Example:
main:
pwm 4,150,20 ‘ send 20 pwm bursts out of pin 4
pause 20 ‘ pause 20 ms
goto main ‘ loop back to start


And the pwmout command can only be used on pin 2, which is not easily unsoldered.

I currently have it at pwm,0,255,10. I don't really understand what duty is, at anything under 200 there is a whining noise, and under 75 it wont even move.

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paulsobczak
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Re: April Maker Challenge!!!!

Postby paulsobczak » Fri Apr 10, 2009 10:57 pm


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jtbarclay
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Re: April Maker Challenge!!!!

Postby jtbarclay » Fri Apr 10, 2009 11:06 pm

paulsobczak wrote:http://en.wikipedia.org/wiki/Duty_cycle

haha thanks

uptownmaker
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Re: April Maker Challenge!!!!

Postby uptownmaker » Sat Apr 11, 2009 11:41 am

What do you have providing the muscle of the drive current?

If you're trying to drive your motor directly from the pin you are almost certainly going to be out of luck. A PIC pin can push maybe 20mA and most motors won't even get out of bed for less than 100.

If your motor is unidirectional, you can get away with a circuit like the one I provided for your fan- driving the base/gate of an N-type power transistor. If you need bi-directional control, that's tougher, because you need an H-bridge and two I/O pins, and you need to change your PWM value because going forward at 75% of the maximum speed will require a 75% duty cycle but going backwards at a 75% speed requires a 25% duty cycle.

I think I just had an idea for another class- power load switching with the Arduino: how to turn on lights, run motors, adjust heating element temperatures and do other high-power stuff with the Arduino.

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jtbarclay
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Re: April Maker Challenge!!!!

Postby jtbarclay » Sat Apr 11, 2009 6:37 pm

nope, it's just bringing pins to the transistor/fet/mostfet/whatever that's on the board already in the car high.


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