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Spockie-Tech
Site Admin
Joined: 31 May 2004
Posts: 3160
Location: Melbourne, Australia
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Depending on your goals, The AVR/Atmel family might be worth considering as well. Each has plus and minuses.
My impressions after comparing the two are that Atmel/AVRs are more popular in the younger, DIY, Open-source, and power/$ area. Their internal architecture and instruction set is more logical and understandable. Google "Arduino" for some nifty examples of the types of development widgets and environments available
The PIC range seems to a bit more popular in older-school developers, there are more commercial-tools available for them (often at big $ prices), and they have some strange architectural quirks and programming techniques that are probably a result of legacy design compatibility choices since they are older than the AVRs (afaik).
Using a high level language/interface like PicAxe's or GCC can mask a lot of the weirdness of either range for you. If you are going to work with Jake, He likes PIC's runing JAL. I like the feel of the AVR community better myself (www.avrfreaks.net)
As a generalisation, to me, The Pic People feel like the Windows community.. Lots of commercialisation, trade-secrets, proprietary, do it by buying our $ gadget stuff. The AVR people feel more like the Linux, open source, help newcomers, here are the schematics to DIY type. Thats just my subjective impression of the two though. Hardware wise, both are equally capable.
www.dontronics.com (Australian but pricey), www.sparkfun.com www.olimex.com www.avrfreaks.net are good sources for every dev widget you can think of in both familys _________________ Great minds discuss ideas. Average minds discuss events. Small minds discuss people
Last edited by Spockie-Tech on Thu Jun 26, 2008 4:43 pm; edited 1 time in total
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Thu Jun 26, 2008 12:57 pm |
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Spockie-Tech
Site Admin
Joined: 31 May 2004
Posts: 3160
Location: Melbourne, Australia
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In general yes. An I/O pin is a I/O pin regardless of the family.
There might be some minor differences wrt to Analog/Digital convertors, inbuilt special functions (PWM, Interrupts) and the like.. but they vary just as much from model to model within each family as they do across the families anyway. Some chips have more current drive capability, some have lower power consumption, or more sensitive ADC's etc.
If theres any tricky analog interfacing going on, you want to check the data for the particular chip you are using, regardless of family, but for basic I/O tasks like driving other chips, Leds, Relays etc, they are fundamentally the same. _________________ Great minds discuss ideas. Average minds discuss events. Small minds discuss people
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Thu Jun 26, 2008 1:59 pm |
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Spockie-Tech
Site Admin
Joined: 31 May 2004
Posts: 3160
Location: Melbourne, Australia
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That Ap note is a good broad overview of the general principles involved in single direction low power ESC design, but the gate drive section is not even in the ballpark for high current use.
a Pull-Up resistor on the gate (to charge it), with a simple pull-down transistor opposing it has no chance of pumping the current in and out of the gate capacitance fast enough to bring the Fet anywhere near its maximum current rating (by minimising switching time).
Indeed their test results show a 500nS rise time and 1000nS fall time for the gate, which is too long for pushing a Fet to its limits. You want to be thinking down in the 10's of Nanoseconds, not hundreds to thousands.
Also, remember its not the 0 to saturation times that matter, but the threshold-to-saturation, since below threshold the Fet isnt conducting at all, so its not burning power.. once you get over the threshold voltage, then you need to hurry things along into sat. at high power levels
OK for a little 10amp ESC, but pulling peak currents of 100amps with switching times like that will result in rapid "mesoplasma formation" (yes, thats a real term - inside your fet causing significant device derating, even extrapolating to zero functionality (this verbiage is from an IRF datasheet )
The gate needs a very low impedance drive so it can move charge in and out quickly, pull-up and pull-down resistors are not low impedance.
Other than that point, it overall looks good _________________ Great minds discuss ideas. Average minds discuss events. Small minds discuss people
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Wed Jul 02, 2008 12:59 am |
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