[GPS_Standard] VE2ZAZ

Tue Jun 8 12:03:37 EDT 2010

Hi Jacques,

I’m not using that circuit on this application, but it could be tuned for
it. Yes, 200nS is quite a long time.

The PPS output can deliver up to 5mA, so we could lower the 10K resistor
down to drive the gate capacitance harder, and bring the rise time to
shorter times (note we actually need to sink current in this application)

Note that the rise time from the Resolution-T directly is “typically less
than 20 nanoseconds”, so it may not be very important to have a very fast
pulse as long as the trigger level of the Schmitt Trigger in the PIC remains
constant over time (which should if we keep temperature and supply voltage “
constant”)

Regards,

Roberto EB4EQA

From: jacques audet [mailto:jaudet at hotmail.com] 
Sent: martes, 08 de junio de 2010 17:20
To: rbarrioss at msn.com
Cc: gps_standard at mailman.qth.net
Subject: RE: [GPS_Standard] VE2ZAZ

Hi Roberto,

Your MOSFET level shifter is very simple.
The HI level is made up by the 10K pull up resistor, when
the MOSFET turns off.  It might be a good idea to remove the 
47K resistor to ground on Bert's circuit, since this will limit the HI
level to +4.1V.
Also the pulse rise time will be approx. 10 K * 20 pF = 200 nsec.
Is this fast enough for the reference rising edge ?

regards,

Jacques VE2AZX

> From: rbarrioss at msn.com
> To: ve2zaz at sympatico.ca
> Date: Tue, 8 Jun 2010 16:50:59 +0200
> CC: gps_standard at mailman.qth.net
> Subject: Re: [GPS_Standard] VE2ZAZ
> 
> Hi Bert,
> 
> Yes, the falling edge from the GPS PPS output is not synchronized to
> GPS/UTC. The level converter should not invert the input or we will have
to
> cascade two level converters of this kind. But I was referring to a FET
> based level converter which does not negate the input, such as:
> 
> http://www.sparkfun.com/datasheets/BreakoutBoards/Level-Converter-v10.pdf
> 
> I started to use n-channel enhacement MOSFETs for this applications after
> finding a simple and very effective 2N7000-based TTL to RS232 converter.
> 
> Sorry, I should have made it more clear. The first thing that comes to
mind
> is using an NPN transistor which will obviously put the controller board
to
> respond to the falling edge of PPS, which is not what we want.
> 
> Thanks, it's great to have you personally on the list answering questions.
> 
> Roberto EB4EQA
> 
> -----Original Message-----
> From: Bert, VE2ZAZ [mailto:ve2zaz at sympatico.ca] 
> Sent: martes, 08 de junio de 2010 16:04
> To: rbarrioss at msn.com
> Cc: gps_standard at mailman.qth.net
> Subject: RE: VE2ZAZ
> 
> 
> Roberto,
> 
> You need two transistors to do the trick. One transistor will invert and
> make the GPS 1 PPS falling edge become the rising edge into the
controller.
> You don't want this. It is the 1 PPS rising edge that must be used and the
> controller triggers on a rising edge.
> 
> Bert, VE2ZAZ
> 
> ----------------------------------------
> > From: rbarrioss at msn.com
> > To: ve2zaz at sympatico.ca
> > CC: gps_standard at mailman.qth.net
> > Subject: RE: VE2ZAZ
> > Date: Tue, 8 Jun 2010 15:46:06 +0200
> >
> > Hi Bert,
> >
> > You are right, Schmitt Trigger inputs have a 4V minimum voltage 
> > requirement for Vih. I did not think about the buffer type when 
> > checking their compatibility...
> >
> > It is somehow working fine for me, but the proper way to do it would 
> > require a level converter. Since GPS a controller share a common 
> > ground, I think a transistor plus two resistors for the high state would
> work.
> >
> > Thank you,
> > Roberto EB4EQA
> >
> > -----Original Message-----
> > From: Bert, VE2ZAZ [mailto:ve2zaz at sympatico.ca]
> > Sent: martes, 08 de junio de 2010 13:46
> > To: Roberto Barrios
> > Subject: VE2ZAZ
> >
> > Hi Roberto,
> >
> > I go by memory here, but I think the minimum-high spec on the TTL 
> > input of the PIC is 4V. It may work in your case, but I know it did 
> > not for some other users. You are probably very borderline and your 
> > performance may degrade over time/temperature.
> >
> > 73,
> >
> > Bert, VE2ZAZ
> > http://ve2zaz.net
> >
> > Roberto Barrios wrote:
> >> Hi Bob, Bert,
> >>
> >>
> >>
> >> I've got one Resolution-T running on my VE2ZAZ standard. The datsheet 
> >> says
> > somewhere it's (3.3V limited) output is TTL compatible. Yes, some 
> > interfaces are pickier than others, but my PCB from Bert is working 
> > fine without further modifications.
> >>
> >>
> >>
> >> I agree with Bob, this is a fine GPS timing receiver. Better specs,
> > smaller, less power-hungry and with much more functionality than the 
> > older Motorola Oncores. The software for this receiver (DSPMON) from 
> > Trimble is great, but look for version 1.53, not earlier.
> >>
> >>
> >>
> >> Regards,
> >>
> >> Roberto Eb4EQA
> >>
> >>
> >>> Message: 1
> >>> Date: Sun, 6 Jun 2010 20:09:33 +0200
> >>> From: "Stig Kristiansen - OZ3XO." 
> >>> Subject: [GPS_Standard] preferred GPS
> >>> To: 
> >>> Message-ID: <33FE5497EB6C4EC7A70EF8E1010971B0 at 3XO>
> >>> Content-Type: text/plain; charset="iso-8859-1"
> >>>
> >>> Hi Bob.
> >>>
> >>> This 12-Ch GPS is very stabile.
> >>> http://www.trimble.com/timing/resolution-t.aspx?dtID=overview
> >>> Extremely accurate 1-PPS output, synchronized to GPS or UTC within 
> >>> 15 ns (one sigma)
> >>>
> >>> Stig - OZ3XO.
> >>>
> >>>
> >>>
> >>> ------------------------------
> >>>
> >>> Message: 2
> >>> Date: Mon, 07 Jun 2010 07:59:36 -0400
> >>> From: "Bert, VE2ZAZ" 
> >>> Subject: [GPS_Standard] VE2ZAZ
> >>> To: "Stig Kristiansen - OZ3XO." 
> >>> Cc: gps_standard at mailman.qth.net
> >>> Message-ID: 
> >>> Content-Type: text/plain; charset=ISO-8859-1; format=flowed
> >>>
> >>> Stig,
> >>>
> >>> Great GPS, but be careful as it is a 3.3V unit. The 1 PPS is not 5V 
> >>> TTL compliant. It will not directly drive the PPS inputs of many 
> >>> controller boards such as mine. You will need to scale up the 1 PPS 
> >>> using a complementary pair of transistors, for example.
> >>>
> >>> 73,
> >>>
> >>> Bert, VE2ZAZ
> >>> http://ve2zaz.net
> >>>
> >>> Stig Kristiansen - OZ3XO. wrote:
> >>>> Hi Bob.
> >>>>
> >>>> This 12-Ch GPS is very stabile.
> >>>> http://www.trimble.com/timing/resolution-t.aspx?dtID=overview
> >>>> Extremely accurate 1-PPS output, synchronized to GPS or UTC within
> >>>> 15 ns (one sigma)
> >>>>
> >>>> Stig - OZ3XO.
> >>>>
> >>>> ______________________________________________________________
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> >>>>
> >>>
> >>>
> >>> ------------------------------
> >>>
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> >>>
> >>> End of GPS_Standard Digest, Vol 35, Issue 3
> >>> *******************************************
> >>
> >>
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> >>
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> 
> 
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