DPRG mailing list archives: [DPRG] BristleBot

Sat Jan 5 16:27:02 CST 2008

Hey Ron,

> I guess my tiny13 won't be driving the beasties.
> I really like the idea of not having to involve an h-bridge or driver
transistors/fets -- too much complexity.

Oh, transistors are our friends!  And they work with no nasty opcodes to
remember.

Here's a new (to me) transistor that might do the trick.  3V looks marginal,
though.  Using a  5V supply, these will work great.  (~300mA with a Vgs of
4V)

It's a 2N7002, an N-channel FET made for low-voltage power switching.

http://www.fairchildsemi.com/ds/2N/2N7002.pdf

I'll buy some of the thru-hole parts with my next Digi-Key order, and let
everyone know how they work.

-Jeff

On Jan 1, 2008 7:23 PM, <DeltaGraph at aol.com> wrote:

>  Hey Jeff, Thanks
>
> Thinking on PWMing motors
>
> I guess my tiny13 won't be driving the beasties.
> Maybe Tiny26 -- Dale mentioned that part drives 40 mA per pin - so I
> looked it up
> 200 mA for total  part -- so reasonable.  So I assume could tie 3 pins and
> pretty much drive motor.
>
> Of course would lose out on direct PWM output, but PWM gen can generate
> soft interrupts which could
> be used to twiddle bits on multiple pins.
>
> Tiny26 will run at 3 volts -- could always current limit motors just a tad
> with series resistance.
> I assume motors would not kill Tiny's pins with flyback spikes. Oh well,
> $2 down the drain if they do.
>
> I really like the idea of not having to involve an h-bridge or driver
> transistors/fets -- too much complexity
>
> I know connecting 24 volts to an AVR pin will blow it.
> Did get away with driving one on a Mega128 to almost dead short (8 ohm
> speaker) for some time and it survived. The chip was running real hot --
> then I discovered a series resistor was shorted.
>
>
> Ron
>
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> ------------------------------
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