[ntp:questions] Trying to use Dimension 4 time keeper

Dennis Ferguson dennis.c.ferguson at gmail.com
Wed Sep 25 16:55:21 UTC 2013


On 25 Sep, 2013, at 12:04 , John Hasler <jhasler at newsguy.com> wrote:

> I wrote:
>> I'm suggesting adding an open-collector driver rather than adding a
>> network of resistors and diodes.  Fewer parts and better results.
> 
> unruh writes:
>> Probably. I'm a bit worried if the base voltage is higher than the
>> collector.
> 
> A single transistor with a base current limiting resistor would work
> fine but I had in mind an IC such as the 7407.

If you are doing it with an IC a 3.3V buffer with overvoltage
tolerant inputs would be better.  A 74HC4050 run at 3.3V would
probably do it, if you don't need input protection (against >15V or
<0V inputs) it needs no additional external components.

Dennis Ferguson

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