4 ms·
Hi HN! I wanted to share the story of µWWVB, a watch stand that I built that automatically sets the time on my atomic wristwatch. Because I can't receive the r
by anishathalye 10y ago
Hi HN! I wanted to share the story of µWWVB, a watch stand that I built that automatically sets the time on my atomic wristwatch.
Because I can't receive the regular atomic watch radio signal where I live, I built a device that determines the current time by using GPS and then emulates the WWVB protocol to set my atomic watch.
In the process of building this, I learned a lot about time, clocks, radio, and WWVB, and so I thought I'd share what I had learned.
- madengr 10y agoVery nice work! Can you receive WWVB via a larger, resonant loop antenna; say a 10 cm diameter solenoid and resonating capacitor? If so, you may be able to place the watch at the center of the resonator (i.e. within the solenoid) so it parasitically couples. The antenna gain will be proportional to area, so much more gain than that of a watch antenna.
- anishathalye 10y agoOh, that's a neat idea! Yeah, I think I should be able to receive WWVB in my dorm room via a larger antenna. I should try it when I'm back in my dorm room after the winter break.
- madengr 10y agoMaybe build one with a short piece of large diameter PVC pipe as the coil form. Use a signal generator at 60 kHz to drive a smaller, transmit probe coil. Then another receive probe coil hooked to an oscilloscope. Use this loose magnetic coupling technique to tune the large coil for resonance. You'll of course want to shoot for as high of Q as possible, but that's an engineering trade off of AC wire resistance, capacitor Q, etc. Go for as large of inductance as feasible, until your self resonance is just above 60 kHz, then pull it to down on frequency with a silver mica cap, or adjustable air variable cap.
- leblancfg 10y agoGreat stuff! I should add, "10s of nanoseconds" took a while to digest. Can I suggest "tens" instead?
- anishathalye 10y agoGood point, I hadn't noticed that. Fixed!
- trav4225 10y agoHi. Thanks for the article! Perhaps I missed it, but I'm wondering why you had to deal with daylight savings at all. Isn't all the time data involved here either UTC or GPS?
- anishathalye 10y agoWWVB includes information about daylight savings time in the information it broadcasts.
- trav4225 10y agoAh, I see. Thank you!
- nathan_f77 10y agoFantastic post! I learned a whole lot by reading this. You also have access to some very nice milling and 3d printing equipment. That is one beautifully designed and soldered PCB.
- amagumori 10y agoelectronic equipment too. i was salivating at that agilent mixed-signal oscilloscope, that's like a $3500 piece of kit. meanwhile i'm over here with my puny rigol ds1052e
- anishathalye 10y agoYeah, I'm lucky to have access to some really nice equipment at the Cypress Engineering Design Studio makerspace at MIT!
- newman314 10y agoThis is cool! Have you given any thought towards building a home GPS powered NTP server? That would be a cool variant on your project.
- grandsham 10y agoThe way that the author uses GPS to get time (NMEA messages) works well for the purposes of the article, eg syncing a wristwatch to ~1 second accuracy. As another poster pointed out though, these messages are only accurate to about a half-step one, and it is actually worse than just using an internet NTP signal. If you want to build a GPS based NTP server, you need a GPS board that outputs a PPS signal. When I built mine I used an adafruit board hooked up to a raspberry Pi's GPIO pins. It's something of a bear to get everything to play together properly and get the extremely precise PPS signal to the NTP server, I recall it required a custom kernel module and a lot of tinkering with tick rates.
- gonzo 10y agoI watched (and guided, some), my son do this in his summer between high school and college. http://store.netgate.com/Lures/GPS.aspx http://store.netgate.com/Lures/GPS.aspx