of precise time and frequency
measurement
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 (~100ppm/C or so)
To reduce the
art ; Discussion of precise time and frequency
>measurement
>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 relativel
: [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 which acts as a synchroniser and produces
effectively about 7K, and C2 120pf.
Bob
>
> From: Bruce Griffiths
>To: Discussion of precise time and frequency measurement
>Sent: Tuesday, February 18, 2014 9:35 PM
>Subject: Re: [time-nuts] TIC model
>
>
>The attached circuit schematic il
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 buf
> 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.
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 inter
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 divide
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
runnin
On Sat, Feb 15, 2014 at 7:10 PM, Tom Van Baak 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
> interrupts somehow?
>
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
ll address them to the list, you, or
Richard as seems appropriate, if that's OK.
Bob
>
> From: Tom Van Baak
>To: Discussion of precise time and frequency measurement
>Sent: Saturday, February 15, 2014 7:33 PM
>Subject: Re: [time-nuts] TIC
directly.
/tvb
- Original Message -
From: "Bob Stewart"
To: "Discussion of precise time and frequency measurement"
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
easy place to start. In fact, there are lot of things I can do
with the 1PPS and an RC to get some experience working with the ADC.
Bob
>
> From: Lars Walenius
>To: "time-nuts@febo.com"
>Sent: Saturday, February 15, 2014 5:13 PM
>
> 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 c
>>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 everyth
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
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 doin
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