[GPS_Standard] VE2ZAZ

Tue Jun 8 10:50:59 EDT 2010

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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>>>
>>> End of GPS_Standard Digest, Vol 35, Issue 3
>>> *******************************************
>>
>>
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