, February 18, 2014 9:35 PM
Subject: Re: [time-nuts] TIC model
The attached circuit schematic illustrates how this might be implemented.
Faster logic devices can be substituted.
R2, C2 approximate the equivalent input circuit of the ADC.
R2, C2 values will vary for each ADC.
The Shift register
Stewart b...@evoria.net; Discussion of precise time and frequency
measurement time-nuts@febo.com
Sent: Thursday, February 20, 2014 3:07 AM
Subject: Re: [time-nuts] TIC model
R2 is dominated by the adc sample switch on resistance and thus has a
relatively high tempco (~4000ppm/C).
C2 has
...@evoria.net; Discussion of precise time and frequency
measurementtime-nuts@febo.com
Sent: Thursday, February 20, 2014 3:07 AM
Subject: Re: [time-nuts] TIC model
R2 is dominated by the adc sample switch on resistance and thus has a
relatively high tempco (~4000ppm/C).
C2 has a relatively low tempco
as effectively about 7K, and C2 120pf.
Bob
From: Bruce Griffiths bruce.griffi...@xtra.co.nz
To: Discussion of precise time and frequency measurement time-nuts@febo.com
Sent: Tuesday, February 18, 2014 9:35 PM
Subject: Re: [time-nuts] TIC model
The attached circuit
Another variation is to use a single 125 style buffer device (eg
74LVC1G125) to charge and discharge a capacitor (in reality an RC
network when the ADC input is taken into account) via a series resistor.
The input to the buffer is driven by the input to a conventional
synchroniser whilst the
On Sat, Feb 15, 2014 at 7:10 PM, Tom Van Baak t...@leapsecond.com wrote:
For Arduino and other less fortunate uC you can always use external chips
to obtain optimal and jitter-free charge/discharge timing. I'm not that
familiar with Atmel chips; could capture/compare be used instead of
You all are inventing problem. Solve them AFTER you find a problem you
can measure. Interrupts are not an issue on a UP like the AVR because
they are completely deterministic. It don't matter the lenth of time as
long as it is 100% deterministic and predictable. On a multi-tasking OS
running
The response time to an external asynchronous interrupt is never
deterministic.
The external interrupt has to be synchronous with the uP clock to avoid
the non deterministic synchronisation delay.
Even when the external event is synchronous with the clock input to the
uP and the uP uses a
Hi Bruce
You are absolute right that it is wise to put some time in the estimation of
such effects as asynchronous Clocks. An iteration between thinking and
building seems always to be necessary but we all have different capabilities
for that. For the Arduino I came to an end with the
Another question: Does a PIC not need overflow interrupts to count say
500 counts as I do in the Arduino?
Lars,
For precision work you must avoid having more than one interrupt. Otherwise
there is the chance both will occur at or too near the same time and introduce
unexpected latency.
Tom tried to steer me to the PICTIC recently, and I sort of brushed him off,
because, quite frankly I didn't understand. Now that I've really looked at it,
it's a much better idea than using a dsPIC33 and brute-forcing it. But, I
don't really need everything the PICTIC offers so I started
Bob Stewart wrote:
Tom tried to steer me to the PICTIC recently, and I sort of brushed him off, because, quite frankly I didn't understand. Now that I've really looked at it, it's a much better idea than using a dsPIC33 and brute-forcing it. But, I don't really need everything the PICTIC offers
Bob Stewart wrote:
Tom tried to steer me to the PICTIC recently, and I sort of brushed him off,
because, quite frankly I didn't understand. Now that I've really looked at
it, it's a much better idea than using a dsPIC33 and brute-forcing it. But,
I don't really need everything the
What Bruce says about interrupts is also worth to check in real life as
“jitter” due to unexpected interrupts or different timing may give problem.
In the Arduino GPSDO the timer1 overflow interrupt may delay the 1PPS
interrupt about 3us and delay the ADC conversion 3us. This is not so
: [time-nuts] TIC model
What Bruce says is really important.
For the ATmega328 the datasheet says 14pF sampling capacitance and nothing
about temperature coefficient.
It also specifies a series resistance 1..100k. So not very precise. If it is
100k the time constant is 1400ns!
I have tested
- Original Message -
From: Bob Stewart b...@evoria.net
To: Discussion of precise time and frequency measurement time-nuts@febo.com
Sent: Saturday, February 15, 2014 5:19 PM
Subject: Re: [time-nuts] TIC model
Hi Lars,
I'm lucky in that I'm starting with a PIC running internally
to the list, you, or
Richard as seems appropriate, if that's OK.
Bob
From: Tom Van Baak t...@leapsecond.com
To: Discussion of precise time and frequency measurement time-nuts@febo.com
Sent: Saturday, February 15, 2014 7:33 PM
Subject: Re: [time-nuts] TIC model
Rather then trying to model the capacitor why not build a reliable clock
and sample the clock before and after the signal you are trying to measure.
In other words you calibrate using a (say) 1 uSec pulse. That would
cover the case of passive parts aging.
On Sat, Feb 15, 2014 at 3:13 PM, Lars
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