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Old 07-14-2009, 04:05 AM   #2001 (permalink)
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Two extra instructions..OUCH!....ha ha ha...
Seriously though, the OC lock out circuit has been designed into the product so the related piece of software should be a "must include". So add the extra instructions (clean up the development notes etc) and mark it compulsory.


As far as the pull down is concerned the jury is out...a uP can fail with the output high as well.

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Old 07-14-2009, 04:46 AM   #2002 (permalink)
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Quote:
Originally Posted by MPaulHolmes View Post
The 1N4148 diode pulls PWM low while !CLEAR is active
Actually this is not guaranteed. The ATmega8 output when low can be as high as 0.7V. The diode forward voltage will be 0.7V or more meaning you are only certain of pulling the PWM signal down to 1.4V which is around the threshold of the input low condition of the CMOS NAND gate input. If you really want to have a hardware circuit I would use an AND gate with PWM and !CLEAR as inputs. (or a NAND gate followed by a NAND Invertor). Or (shudder) a transistor circuit.

Having diodes in digital logic circuits is something to avoid....except zeners as voltage protection devices.
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Old 07-14-2009, 12:12 PM   #2003 (permalink)
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I resoldered the stuff that I removed in the debugging process. It's all a go, I repeat, everything is a go! With it all working perfectly, I believe. I am going to put it in the car later.

I have a way to tune my PI loop now. I'll use the serial port to output the current so I can look at step response. I'm getting a super cheap laptop on Craigslist if it isn't sold already. This is going to be awesome! I remember Jay's graphs if his robot PD loop, and I'm going to try something similar. I can't wait to get good solid data! Then Joe and Adrian can tune to their motors too, and we can get something of a library together, so we know the just right P and I for each motor type.
//////////////////////////////////////////////////////////////////////////////
R12 keeps pwm output low as the default
R11 keeps the current draw from the PB1 down
The 1N4148 diode pulls PWM low while !CLEAR is active

ya!
Paul, what specs do you need in the super cheap laptop? I picked up a pile of laptops a while ago that were chucked out from the college (we have an electronics Bone Yard!), and I believe some of them work, I just haven't cleaned them out yet. If any check out, you can have one. (Runs to Bone Yard.....)
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Old 07-14-2009, 12:29 PM   #2004 (permalink)
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Quote:
Originally Posted by squiggles View Post
Actually this is not guaranteed. The ATmega8 output when low can be as high as 0.7V.
Hey Squiggles!

On pg. 265 of the ATMega8 datasheet, it has a graph called:

Figure 149. I/O Pin Sink Current vs. Output Voltage (VCC = 5V)

The current will be 5v / 10K for the pulldown, plus 5v / 1K for the PWM series resistor. That makes 5.5mA, which makes for approximately 0.2v. 0.2v + 0.7v is safely under for the HC74 family to be considered low. I see what you mean, though.



TheSGC: I need something that will run AVR Studio from Atmel, and that can function as a hyperterminal. I need to be able to get AVR Studio onto the computer, and I have one of those little plug things that go into the usb port. The older one I have doesn't have the right drivers to be able to read it. I think that's it.
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Old 07-14-2009, 12:33 PM   #2005 (permalink)
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AVR Studio® 4 is the new professional Integrated Development Environment (IDE) for writing and debugging AVR® applications in Windows® 9x/NT/2000/XP/Vista(32- and 64-bit) environments.

AVR Studio 4 includes an assembler and a simulator.

haha! I guess it needs at least Win 98. haha! I heard win 95 doesn't work.

EVRag was going to loan me his, so I might not need a permanent one for a little while.
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Old 07-14-2009, 12:55 PM   #2006 (permalink)
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Originally Posted by MPaulHolmes View Post
AVR Studio® 4 is the new professional Integrated Development Environment (IDE) for writing and debugging AVR® applications in Windows® 9x/NT/2000/XP/Vista(32- and 64-bit) environments.

AVR Studio 4 includes an assembler and a simulator.

haha! I guess it needs at least Win 98. haha! I heard win 95 doesn't work.

EVRag was going to loan me his, so I might not need a permanent one for a little while.
I have one here, a Gateway Solo 500 MHz Celeron, 32 MB Ram and a 4 GB hard drive and I am installing a fresh copy of Windows 2000. The battery is probably shot and there is a chunk missing from the case, but it is working and almost done with the Windows 2000 install. I will even install AVR Studio and make sure it works!
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Old 07-14-2009, 01:14 PM   #2007 (permalink)
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Old 07-14-2009, 06:28 PM   #2008 (permalink)
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Quote:
Originally Posted by MPaulHolmes View Post
Hey Squiggles!

On pg. 265 of the ATMega8 datasheet, it has a graph called:

Figure 149. I/O Pin Sink Current vs. Output Voltage (VCC = 5V)

The current will be 5v / 10K for the pulldown, plus 5v / 1K for the PWM series resistor. That makes 5.5mA, which makes for approximately 0.2v. 0.2v + 0.7v is safely under for the HC74 family to be considered low. I see what you mean, though.
Actually you mean 5v / (10k + 1k) = 4.55mA + the uA feeding gate inputs, when the Output pin is high.

I believe the graph on P265 is showing you how much current an output pin can sink at a particular voltage. So a max of 30mA at 0.7V 25DegC

The table on page 242 shows that an output pin can be a max of 0.7V when the output is set low. Way back in my schooling days this was the figure we designed too.

Last edited by squiggles; 07-14-2009 at 06:45 PM..
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Old 07-14-2009, 07:44 PM   #2009 (permalink)
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Quote:
The current will be 5v / 10K for the pulldown, plus 5v / 1K for the PWM series resistor. That makes 5.5mA, which makes for approximately 0.2v. 0.2v + 0.7v is safely under for the HC74 family to be considered low. I see what you mean, though.
Hi Paul, I don't think your calcs are quite right here. The resistors do indeed add in series, but the current therefore drops.

Anyway I think this is how it is ..
(approximated I/Os as 25R source / sink resistance)

PWM !CLEAR D3Anode D3Kathode (Volts)

LO LO 0 0
LO HI 0 5
HI LO 0.8 0.1 PWM source 4.1mA, !CLEAR sink 4.0mA
HI HI 4.5 5 PWM source 0.45mA

The above of course assumes that the I/O's were set as outputs! LOL.

cheers Rob
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Old 07-14-2009, 07:47 PM   #2010 (permalink)
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Hmm, see my table's screwed up, but you get the idea!

Rob

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