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Thread: ARP: Mega 8 or mega 16/32 a few more questions

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  1. #1
    Administrator T-1000 vikas's Avatar
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    Default ARP: Mega 8 or mega 16/32 a few more questions

    Hi all

    Im planning such that everything can be bundled under Rs 500 ... 12 $ .

    Im back with the ARP platform - Itll be based on the Rock platform ( 2002 circuit cellar winner ). Now ill like to ask you guys whatll be better a Mega 8 ( 28 pin ) or Mega 16/8535 etc + ( 40 pin ) ... obviously mega 16 is better but its almost double the price ( MEga 8 is abt Rs 120 while other similar 40 pin IC are about Rs 230 + ) .

    Also one more thing - is putting a L293d ( rs 90 - 120 ) better or a transistorized Hbridge ( Rs 20 - Rs 30 ).

    Think about the price/performance factor with gets a better deal.

  2. #2
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    I tend to use the same board in all of my projects. I think, if ur building it for reuse better not compromise for a couple of hundred bucks. Lot of time n effort goes into building this stuff. make one using a uC with more i/o pins n other features so that u dont have to run around building another bord just because u need a few more pins.

    about the h-brigde- L293/L298 should be your choice. I dont know why so many ppl run 12V motors on L293Ds connected in parallel, L298 has much higher current rating (2A/channel) and is available at the same price
    Building ur own H-bridge is also a good idea.

    Lastly, (for newbies atleast), the cost doesn't matter that much as long as they can properly put together what they buy. I have a huge collection of chips n transistors which I had bought when I started but cudnt figure out what went wrong with the circuit. Thats a total waste of money.
    Using discreete components also means more wiring, n more time to build.

    Also make provision for I2C bus. for adding special chips like RTC, temp. sensor, eeprom, ADC/DAC etc.

  3. #3
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    Hi Vikas,

    I think Mega8 will make a nice choice...as most of the beginners perfer cheap and easy initial. Regarding h-bridge its quite difficult to make a decision....as LD293 is a bit costly....but if there is enough room transistorized bridge is good enough.

  4. #4
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    Mega 8 or better really depends upon your needs that how many io lines you r going 2 use. For some serious and innovative stuff mega8 is really small. But for general use it would be the best price-performance ratio, on the other end better avrs can be an investment if u can use the same in your different projects.

    I just made a 5amp dual hbridge with TIP darlington pair transistors and full project costed me just rs. 85. And without using any heat sinks I can get upto 3.5 amp capacity very easily, with a normal heating. And comparing size, Its smaller in size than L298 and 8 diodes.

  5. #5

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    Hi,

    I think an ATMega16 with a transistorised H Bridge is the best combination. The extra pins on an ATMega16 will allow for more flexibility with regards to the number of sensors, actuators that can be added onto the robot. Assuming that the ARP uses pins as follows

    2 - UART
    6 (3 x 2) - Motor Control
    4 (2 x 2) - Quadrature encoder feed back
    ----
    total 12

    With a mega8 that would leave only 10 pins for all the sensors and actators a user might want to add on.With a mega16 there will be 20 pins left over which would probably be more suitable. ATMega16 is available for Rs 215 here, I think the Rs 85 extra spent on a mega16 in lieu of a mega8 would be worth it.

    With regards to the motor driver, if the same functionality can be reliably attained with a transistor based H Bridge its probably better than using an L293/293D.

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