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vk4tec

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Joined: 24/03/2012
Location: Australia
Posts: 239

Posted: 12:19am 22 Jun 2013

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Hello

I am thinking of making a GPS clock

I would like to use LED display, RTC , mini maximite and TTL GPS

I am thinking I need uart for GPS

I am thinking I need xxx for RTC

I can use pins or SPI for LED max7910

What would an RTC use ?

The idea being the RTC can be used when GPS lock is lost

I have done everything listed here except for RTC

Comments ?

Andrew

Andrew Rich VK4TEC
www.tech-software.net

MicroBlocks

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Joined: 12/05/2012
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Posted: 01:55am 22 Jun 2013

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A GPS clock would not really work good when it is used inside.
For GPS you need a clear view of the sky.
A GPS module needs a UART

If indoor use is what you want you could consider using Wi-Fi to connect to the internet and get a time from one of the many timeservers that are available.
You can get that also to work over a a single UART.

If you add a RTC then update the RTC with information from the timeserver and from that moment on use the information from the RTC.
Most RTC use I2C.

However, why do you want to use GPS (Wi-Fi)?
If it is as a learning project it would be great to get your hands on a GPS, much to study and learn.
Also the Wi-Fi solution would give you much to study.

If it is a project that just needs to tell the time, then only using an RTC and a few buttons to set the time is all you need. The RTC is very accurate and you need to adjust it maybe once a year.

Edited by TZAdvantage 2013-06-23

Microblocks. Build with logic.

cwilt
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Joined: 20/03/2012
Location: United States
Posts: 147

Posted: 05:14am 22 Jun 2013

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It depends on how accurate you want it to be. Some GPS's will work indoors and decoding the NEMA string will get you similar accuracy to using an NTP server with internet lag time. If you were to connect the 1PPS output from the GPS to an IO pin and trigger an interrupt. I think most are rising edge triggered. Accuracy would come down to the speed at which mmbasic can detect trigger and write correct time. I would guess accuracy at 0.1 second or better.

Both methods would benefit from interrupts calling user defined sub routines or functions.

PS.. Just remembered that most RTC's also have a 1PPS output. When used with GPS 1PPS it would be possible to measure time drift over time.

palcal

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Posted: 05:08pm 22 Jun 2013

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I built the 6Digit GPS clock that was in the May and June issues of Silicon Chip Magazine. It works fine indoors and in the article it was stated they put it in a filing cabinet and it still worked. It uses an EM-408 Gps module. Reading the article may help you.
Palcal.

"It is better to be ignorant and ask a stupid question than to be plain Stupid and not ask at all"

MicroBlocks

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Posted: 06:54pm 22 Jun 2013

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It depends in what kind of house you live.
I live in a condominium and my gps (module, telephone, navigation) all stop working because of the concrete structure.
I have to step out on the balcony where my navigation picks up a signal but my phone not.

Microblocks. Build with logic.

Nixie
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Joined: 19/02/2013
Location: Australia
Posts: 66

Posted: 03:18am 23 Jun 2013

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YES! A GPS clock to provide the accuracy is also what I am building; this is to replace the RTC in the CMM and provide an RTC for the MMM.

The CMM I have just built gains two seconds every 24 hrs. The MMM loses one second every 24 hrs.

I've looked at Talbit's and Geoff's work to do with GPS/ clock; and, before I continue, I thought I'd ask if anyone has considered using the "Deluxe GPS 1pps TIMEBASE for frequency counters" in APRIL 2013 (p 60) Silicon Chip; or the "Extremely accurate GPS 1pps TIMEBASE for a frequency counter" in FEBRUARY Silicon Chip (p74)?

I can see how one could use these as an additional external accessory; but, I wonder if they could be hard wired into either MM - is this possible?

I built Geoff's Boat Computer kit. It works well in a steel shed (with steel roof) without an external antenna, though it is about 30cms from a window.

Thanks, Nic.
VK3COW.

Nixie
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Posted: 03:22am 23 Jun 2013

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Sorry, I meant to add that I think the (loss and gain) changes that I am experiencing with my MMs times are due to large changes in ambient temperature. N

palcal

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Posted: 12:51pm 23 Jun 2013

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If you have trouble with reception get an external antenna. I bought one from Deal Extreme for $5 and it plugs straight into the GPS module.
Palcal.

"It is better to be ignorant and ask a stupid question than to be plain Stupid and not ask at all"

vk4tec

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Joined: 24/03/2012
Location: Australia
Posts: 239

Posted: 09:16am 27 Jun 2013

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Hello

My GPS clock is looking like

1. MaxiMite Mini ( jaycar )
2. 12 volts to 5 volts regulator for SDP8 8 x 7 SEG LED display and GPS
3. 12 volts to 3 volts regulator for MaxiMite Mini
4. GPS TTL
5. The SDP8 uses SPI and I can use the SPI on the MaxiMite Mini
6. GPS TTL will use USART - CON 2 pins 3 + 4 (RX and TX)

What would be the SPI pins on a Maximite Mini please ?

- Andrew -

Andrew Rich VK4TEC
www.tech-software.net

Nixie
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Joined: 19/02/2013
Location: Australia
Posts: 66

Posted: 12:32pm 27 Jun 2013

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Hi Andrew,

I have the same question! So I will be looking at responses too!

Don't know if you have the latest Silicon Chip?

There is a circuit to update a RTC using a GPS in "Circuit Notebook", which may be of assistance from a design perspective. But it doesn't answer your Question. Would work well with the CMM.

I need an accurate clock for my MMs. Yesterday, I 'lashed together' the timebase circuit I mentioned above in a previous post (February Silicon Chip); and, took a data lead directly from an EM408A into pin 15 on the MonoMM.

Using Geoff's parsing software GPS.BAS, which I modified for TIme/Date. It works really well. This approach is the minimum of components, just the GPS modle, but then the overhead is in the software.

Regards, Nic

VK3COW

vk4tec

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Joined: 24/03/2012
Location: Australia
Posts: 239

Posted: 09:54pm 27 Jun 2013

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Anyone good at setting the time in a DS1302 RTC ?

I have some assembly code that came with my QL200

But I am having troubles understanding the format.

- Andrew -

Andrew Rich VK4TEC
www.tech-software.net

vk4tec

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Joined: 24/03/2012
Location: Australia
Posts: 239

Posted: 02:13pm 28 Jun 2013

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Here is the QL200 showing time from DS1302 RTC

Cheers

- Andrew - Edited by vk4tec 2013-06-30

Andrew Rich VK4TEC
www.tech-software.net

MicroBlocks

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Posted: 02:47pm 28 Jun 2013

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Andrew,

That 8 digit LED board looks nice.
Where did you buy it and what were the costs?

Microblocks. Build with logic.

vk4tec

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Joined: 24/03/2012
Location: Australia
Posts: 239

Posted: 06:03pm 28 Jun 2013

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Hello

The 8 digit display is from futurelec

It has a max7910 chip

You control it using SPI

Three lines from memory.

Cost need to check the site

SDP8

Andrew

Andrew Rich VK4TEC
www.tech-software.net

Talbit
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Joined: 07/06/2011
Location: Australia
Posts: 210

Posted: 07:16pm 28 Jun 2013

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Gents,
My Garmin GPS/SPI clock is still ticking along nicely. It uses the Futerlec display (took forever to arrive) but there is no RTC with battery backup so if the GPS loses lock and stops sending the NMEA string then the display will freeze. There have been a few ideas of how to set the RTC via the GPS NMEA string but for good accuracy, you need to sync the RTC to the GPS PPS which I would say might be impossible. Remember, the PPS is the only accurate time reference.
Talbit

Talbit

vk4tec

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Joined: 24/03/2012
Location: Australia
Posts: 239

Posted: 08:28pm 28 Jun 2013

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Very good

Yes the PPS is the way to go.

I got a box, GPS maximite mini and SDP8 display

I have a RTC on the Q200 development board.

I am going to migrate from assembly to MMBasic for the final build.

Might be "DD MM.HH.SS" - dunno yet

Having fun, in between flying my quad copter.

Did you see ADAFruit has a nice clock too.

Russian tubes

- Andrew - Edited by vk4tec 2013-06-30

Andrew Rich VK4TEC
www.tech-software.net

vk4tec

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Joined: 24/03/2012
Location: Australia
Posts: 239

Posted: 08:33pm 28 Jun 2013

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I have to do some study about SPI and I2C differences.

The SDP8 is SPI

The DS1302 RTC is I2C I think

I see the maximite has RTC on board - could cheat ;-)

- Andrew -

Andrew Rich VK4TEC
www.tech-software.net

Bryan1

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Joined: 22/02/2006
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Posted: 08:42pm 28 Jun 2013

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Just had a quick look at that Q200 dev board and to me it looks like ching takeoff of the mikroE boards with a similar price tag to the real thing too....

vk4tec

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Joined: 24/03/2012
Location: Australia
Posts: 239

Posted: 12:59am 29 Jun 2013

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LED face plate done

Andrew

Andrew Rich VK4TEC
www.tech-software.net

vk4tec

Senior Member

Joined: 24/03/2012
Location: Australia
Posts: 239

Posted: 01:33am 29 Jun 2013

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Guys,

Am I going to be able to support an RTC with the Maximite mini ?

I have to make a choice now.

1. TTL GPS - yes
2. SPI LED - yes
3. RTC - ???

- Andrew -

Andrew Rich VK4TEC
www.tech-software.net

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