DPRG mailing list archives: [DPRG] Motor backlash / Back EMF

Mon Jan 7 07:13:19 CST 2008

On Mon, 7 Jan 2008 23:01:48 +1000 (EST), Triffid Hunter
<triffid_hunter at funkmunch.net> wrote:

> That's exactly what decoupling capacitors are for. Also remember that cmos 
> chips only take low currents on average - that low current is taken in 
> very very short sniffs of up to a few amps, and they *need* 100nF or so of 
> high frequency capacitor as close to their power pins as possible to keep 
> their voltage good. Even an inch or two of track introduces enough 
> inductance to cause the chip issues. Ceramics are excellent for this, and 
> MKTs should be acceptable. Electrolytics simply don't have the high 
> frequency response to work here, although they work well in parallel with 
> something that does.

I typically put 1 0.1 uF ceramic cap immediately next to the
micro-controller, between the power and ground pins (in each place they are
together). I also put as large an electrolytic cap as I can fit somewhere
between the voltage regulator and the micro-controller. 

On Seeker 2x, my latest mini-sumo, I've got a 0.1 uF cap on each side of
the chip (ATmega128), and a 6.8 volt 220 uF electrolytic between +5 and
ground.

http://www.huv.com/miniSumo/seeker2x/Seeker2x-PCB-Bare.jpg

You can see the brownish 0.1 uF caps to the lower left and upper right of
the chip. The large black box to the left of the chip is the 220 uF
electrolytic.

Later,
Jon

--------------------------------------------------------------
   Jon Hylands      Jon at huv.com      http://www.huv.com/jon

  Project: Micro Raptor (Small Biped Velociraptor Robot)
           http://www.huv.com/blog