wpmcnamara

Member Since: January 6, 2010

Country: United States

  • Something on the order of 12,500G, assuming a 90mph fastball. ∆v of around 27km/s.

  • It would be interesting to program the Clock Select to use the 128kHz internal oscillator and see if the problem remains. The one problem being that you have to suffer through the Arduino bootloader and initialization at 128kHz. Alternatively, you could switch the Clock Select to “external clock” and drive XTAL1 with a full swing square wave. You do run into that “don’t vary the clock by more than 2% per cycle” note that you reference in the video, but it would seem that it shouldn’t cause problems since, as you also not, we aren’t worried about any of the peripherals in this little experiment.

  • The AVR 328P is rated to run down to 0Hz – it is a static core. The same 128kHz oscillator that drives the WDT can be used as the system clock, as can an external 32.768 kHz watch crystal, so you have not done anything from a slow clock perspective that isn’t fundamentally possible.

    I had the same though about the WDT, but it’s max timeout is 8 seconds, not minutes, and certainly not 10’s of minutes. Interesting puzzle you’ve got there…

  • Since we are being pedantic, there are only 29 bits of control per LED. 8 bits for R, G, and B and 5 bits for global drive current. (229)250=27250. That’s a lot a different “colors”.

  • Actually, it has to do with encoding. Up to 2400bps the baud rate and bit rate were equal. After that, you got increases by encoding multiple bits per symbol. 9600bps was four bits per symbol at 2400 baud. 14.4kps, 28.8kbps, and 33.6kbs were encoded on a 3429buad symbol stream.

  • You can cut the price differential to $0.12 per part if you can figure out how to read a potentiometer without using an ADC. But that requires the same math that you have to know to use a 555. :)

  • Take your IRF510. It’s good for up to 5.5A or so. Taking one of the precision gear motors that Sparkfun sells, we find that its stall current at 12V is 1A. So, no immediate problem there. The rDS(ON) is 0.54 ohms. Call it 0.5 ohms for easy math. Fully on, the IRF510 will dissipate about 1/2W at full motor current. By the time the FETs resistance equals that of the motor (12 ohms), the FET will be dissipating 3W due to the voltage drop. Well within it’s capability, but pretty wasteful. This, by the way, is why motor control is PWM, whether with FETs or BJTs. Handling large currents through any sort of variable resistance results in a lot of heat.

    Now, for the professional reason its a bad idea. Assuming you burn one staff day using a 555 for your design and one hour for a microprocessor solution. Totally unrealistic, but it will help prove the point. Using Jameco, because that’s where i was looking at the IRF510 datasheet, the cheapest micro with ADC capability (gotta read that potentiometer) is $0.89 qty 100. The cheapest standard 555 is $0.17 qty100. Let’s assume the quantity discount stops there. Lets assume your engineering time costs $120 an hour. It cost you $120 to design in the microcontroller and $900 to design in the 555. Wow, it’s a lot cheaper to use the micro right? What happens when you make 100,000 of the widgets you just designed. Each micro controller widget costs $0.72 more to make. All of the sudden you spent $72000 more in parts to save $780 in engineering costs.

    The above is a very quick lesson on why something that makes sense in the hobby realm or as a one off solution makes no sense, and may very well doom a product, that will be commercially produced. There is absolutely nothing wrong with using a microcontroller to solve a problem that could be done with a slightly more complex and time consuming, if cheaper job, when you are doing it for yourself. But claiming that the cheaper solution has outlived its usefulness because its old and a bit more complex to understand (depends on your point of view) won’t get very far when presented to people who do design work for commercial projects.

  • I can’t quite make it out in the picture, but who makes that power strip in the last image? I could certainly put a few of those to good use.

  • Perhaps a bit nit-picky as the data sheet calls x8+x2+x+1 a CRC-8, but the oh so helpful table you link specifies it as CRC-8-CCITT with a plain CRC-8 being x8+x7+x6+x4+x2+1.

  • I first learned about charge pumps many moons ago. I built a high voltage charging circuit for a photoflash cap – something like 220uF@450V. I started out with an inverter turning 12VDC into ~100VAC and then running it through a four stage Cockcroft-Walton voltage multiplier. At the time, I didn’t access to a good, high current flyback transformer, nor the knowledge to build the drive circuit. The output of the photoflash cap was used to drive each stage of a coil gun. Took me to state level science fair competition.

    In reference to the timing jitter from the RedBoard. The Atmel timer/counters can be configured to generate complementary PWM signals with dead time. See section 3.1.3 of App Note AVR447 for an explanation. Since you are using a fixed duty cycle, the concern for updating duty cycle values in parallel goes away. This does, of course, require programming the AVR at the chip level and not using the Arduino environment. Tuning the dead time should allow you to increase efficiency some too, though moving to FETs instead of BJTs may help more.

No public wish lists :(