On 10/14/2016 02:01 PM, Gene Heskett wrote:
> On Friday 14 October 2016 14:45:31 Chris Albertson wrote:
>> Typically 0.1 bypass caps REALLY to have to be physically close to the
>> load they are bypassing. Within a few millimeters.  Cut the leads
>> short and bridge the power pins with the cap.
>> Placing a larger cap farther away can't cause any harm but it is not
>> going to do the same job.
>> Reason:  The real world is not the same as theory.   All caps have an
>> internal series resistance (ESR). Think of them as a cap and resister
>> in series and model them that way too when you design the circuit.
>> The  ESR of a .1uF ceramic cap is nearly zero, but for the tantalum,
>> you need to look it up in the data sheet.
>> Why physically close to the load.  Wire has non-zero impedance.
>> Mainly in this case it is inductive.   You need to minimize the value
>> of the inductor between the 0.1 cap and the device.  Apparently the
>> manufacturer wants a low impedance power supply.
>> Draw the circuit schematic with a the lead wire inductance and cap's
>> ESR shown then you can see that needs to be minimized.  Don't worry
>> about space you candy 0.1 caps that are the size of a large grain of
>> sand
> Anyplace of note to source them?

   Here is one in a 01005 package (Metric 0402)   0.016"L x 0.008"W - 
(0.40mm x 0.20mm) :

   They are cheaper than the through hole caps that I normally buy. Hand 
soldering them will be a royal PIMA!

>> The usual way to mount these is to make a tiny PCB that has the device
>> on to and a mounting hole and the passive parts like the capacitor(s)
>> and a connector for the cable.
>> All that said, it will likely work OK if you can get that small ca
>> reasonably close.   Better to get the 0.1 closer then a larger one
>> farther way as the goal is to minimize the amount of wire
>> And using a larger cap is no substitute for the .01 either because I
>> bet the .1 was spec'd mainly for its low ESR, not because it needed to
>> be exactly 0.1uF
> As a CET, I am well aware of all that, including the inductance of 2" of
> wire.
> As for the ESR, tantalums are generally sub ohmic too.  For half a
> century or more. Its reverse bias that nails them to the fence, even a
> few millivolts will do it eventually.
> Any caps on the leads will have to be not longer than the 667 is wide,
> and not more than half its thickness.
> Thanks Chris.
>> On Fri, Oct 14, 2016 at 9:51 AM, Gene Heskett <>
> wrote:
>>> Greetings everybody;
>>> A bit too cold this morning to go out to the shop and saw out the
>>> thicker spacers I am going to need to permanently mount the Z motor
>>> and screw anchor.
>>> So, not wanting to waste the day waiting for it to warm, I went back
>>> to work on the encoder thing this morning.
>>> I now have an additional tab of alu extending to the left to hold
>>> one of these ATS667's as an index pulse generator, and have that one
>>> s-glued in a bit beyond where the center of the glued on screw
>>> passes by, hoping it won't trigger on a regular tooth.
>>> But, I've never used any of these before.  No clue as to their bad
>>> habits.
>>> The spec sheet I have shows a "required" .1 bypass to ground on the
>>> VCC lead, but has anyone had any problems using just one for all 3
>>> devices? This thing is cramped for space for a bulky mylar .1.
>>> So I intend to put an even larger tantalum on the pcb, which will be
>>> on the left face of this added tab as I can let it project inward
>>> nearly 20 mm's in that space, lots of space before encountering
>>> anything that moves there.  That means I'll have to paste some
>>> wrapping wire to extend the leads about 1" to get to the pcb.  So
>>> this bypass cap may be as much as 2" of wire away from the device
>>> body.
>>> Can anyone testify that the extra lead length is a problem?
>>> Thanks all.
>>> Cheers, Gene Heskett
>>> --
>>> "There are four boxes to be used in defense of liberty:
>>>   soap, ballot, jury, and ammo. Please use in that order."
>>> -Ed Howdershelt (Author)
>>> Genes Web page <>
>>> --------------------------------------------------------------------
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> Cheers, Gene Heskett

MC Cason
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