[ntp:questions] Re: Looking for time sync hardware supported under Linux for under $400?

David L. Mills mills at udel.edu
Fri Jan 20 17:48:24 UTC 2006


Hal,

You don't need a MAX232 and besides those things burn out so often mine 
are now socketed. Also, the capacitors required are awkward and don't 
last more than twenty years.

I throw down the challenge. Connect a couple of transistors and a couple 
of resitors as a TTL/EIA level converter. Use the DTR pin forced high 
and RTS pin forced low as voltage sources. There's lots of ways to do 
it. Connect a PNP emitter to DTR and collector to DCD. Connect a 1 K 
resistor from there to RTS. Connect the base to the collector of a NPN 
transistor via a 100 K resistor. Connect the emitter to ground. Connect 
the base via a 1 K resistor to the TTL source. Easy.

Dave

Hal Murray wrote:

>>Terje, what's the power consumption?
>>Low enough to steal power from the RS-232 port?
> 
> 
> Garmin's data sheet says the GPS 18-LVC takes 60 mA.
> 
> TI's data sheet for the MAX207 says typical short circuit current
> is 10 mA.
> 
> It wants between 4 and 5.5 V.  Even if you find a driver with enough
> current, there is no guarantee that the voltage will be reasonable.
> 
> 
> Probably better to use the USB trick.  I've seen similar hacks
> stealing power from the keyboard/mouse connectors.
> 
> On the other hand, I have a SIIG CyberPro/CyberSerial PCI 4S that
> has jumpers setup to feed out 5V or 12V on some pin.  The documentation
> doesn't say which pin or how much current. 
> 




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