Jim, My plan is to make the "10 MHz clock + processor" separate from the GPS module. Ultimately any GPS pps signal should lock the clock.
This is a work in process and may go through several iterations of hardware. The micro has a clock out pin so I may add another BNC + 50 ohm driver to use that. In fact I will incorporate that in the first run. Depending on how it impacts board design. Thanks for the nudge. That would give 50 MHz divided by 1 to 256. The 50 ohm driver uses a '245 with 8 resistors so it will handle a fully loaded 50 ohm line - it is powered by 5V so you can get 2.5 V on a fully loaded cable - assuming your power supply will handle the current. The micro and its real time operating system are in their final stage of development. What would be new for the proposed board is just the addition of the DAC + reference to control the oscillator. The current version just uses a trimpot. And since the offering (both versions) will be bare board you don't have to buy the TCVCXO if you didn't need it. You could substitute a 50ppm or 10 ppm packaged oscillator. The clock pin outs/footprint is the same. I will bring out the DAC voltage suitably buffered for those who want to control something else. But a lot of this is TBD for now. All I'm going to commit to is control of the TCVCXO. For now. And of course I will need to separate the digital side from the analog side as much as possible. But as I said a work in progress. When I do make boards available they will be available indefinitely. Basically the layout goes into a catalog. The trouble with electronics is that nothing lasts. Production wise. This has its good and bad points. I have a very nice stock of 1/4 W 5% resistors that I rarely use since I went to 0603 (mostly) 1% resistors. You can get those for $3 a thousand. I only use 1% resistors in the low level sections of my designs these days. In fact for surface mount - unless you need power resistors - 5% is going out of style. And for prototyping I only do that on PCBs. I use http://oshpark.com/ who charges $5 a sq in for a stack of three. $1.666 per sq in. on a per board basis. About the best price out there and the open areas of the board (holes, pads) are gold plated. Their motto is "We're fab" and they are. Turn around runs two weeks +/-. They don't charge for shipping. Unless you want speed. OSH Park handles my catalog. Simon Engineering is the art of making what you want from what you can get at a profit. >________________________________ > From: Jim Lux <[email protected]> >To: M. Simon <[email protected]>; Discussion of precise time and frequency >measurement <[email protected]> >Cc: "[email protected]" <[email protected]> >Sent: Monday, August 5, 2013 11:01 AM >Subject: Re: [time-nuts] Low cost GPS for model aircraft > > >Design so that when that module is no longer available, you've got pins and >software switches to use something else. Lots of one off projects depend on >something surplus or cheap, and rapidly become non-duplicate-able when the >parts supply ends. > >On Aug 5, 2013, at 1:18, "M. Simon" <[email protected]> wrote: > >> I was looking at this GPS with a PPS output for $22 plus shipping. >> >> http://www.hobbyking.com/hobbyking/store/__31135__neo_6m_gps_module.html >> >> >> I have finally decided to take the plunge and design a low cost frequency >> standard and that module looks like a good place to start. Couple it with a >> cheap micro running at 50MHz with a time capture counter (no one count >> bobbles). The master clock will be a Pletronics TCD-4051-10MHz TCVCXO good >> to .1 ppm over temp (when calibrated). The micro multiplies it up to 50MHz >> (PLL) to clock the micro and counter. Plus a 16 bit DAC and reference. I >> thought I might be able to get as close as 1E-9 short term maybe a little >> better. >> >> >> Software? I plan to roll my own. I will make bare boards available for those >> interested in duplicating my efforts. Software too. The micro will have I2C >> (for an LCD display and any front panel controls/LEDs required) and serial >> (good to 115,200). The serial will give access to USB for those who want >> that. Plus a few spare port pins. >> >> Now my question is: what do you think of the above GPS model? Does anyone >> have experience with it? It is supposedly based on the ublox NEO-6M GPS >> module. >> >> I have also contacted: http://www.inventeksys.com/products-page/gps-modules/ >> To see what they have to offer. >> >> I'm open to any suggestions - as long as the cost is low or I can get free >> samples. And I don't care if I can buy something for less fully assembled >> and tested. I'm a Maker. I want to make it. And write it up for the magazine >> I write for. >> >> Simon >> >> Engineering is the art of making what you want from what you can get at a >> profit. >> _______________________________________________ >> time-nuts mailing list -- [email protected] >> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >> and follow the instructions there. > > _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
