Thanks. Yep running an extra Dc to Dc converter is an option but we already have access to clean 28 and 13.8 VDC supplies with some extra capacity. We could likely provide up to a 100 watts of power for this system (I doubt it would need that much.)
The hold over requirement is in the range of several hours. The temperature swings could be fairly large (ie. cold soak outside at minus 35C, then inside a heated garage, plus what ever temperature the equipment bay rises to when the vehicle has been operating for some time probably less than 85 deg C.) mounting the equipment in locations other than the equipment bay would likely result in lower max temperatures. I'm not sure about the cooling capacity of the equipment bay, but there are other areas with climate control systems where this device could be installed if needed. I'm fairly comfortable that a device that generated up to 100 watts of heat could be accommodated (ie, I would assume all of the electrical power going into the device gets turned into heat) but would need to double check this. The size is somewhat flexible. To a certain extent the requirements could be adjusted to fit an existing COTS product that was perceived as generally suited to the application. As this is a one off requirement, that will be in use for a limited time some limitations can be worked around or lived with. The budget could be several thousand dollars. I thought about a Raspberry Pi type of solution, but need to factor in the cost of my time or that of someone else, plus there is a strong desire to either drop in a COTS "black box" or use a laptop. Thanks for the comments. Sent from my iPad On 2015-05-12, at 3:54 PM, Pete Stephenson <[email protected]> wrote: > On Tue, May 12, 2015 at 7:11 PM, Mark Spencer <[email protected]> > wrote: >> Hi sorry for a possibly OT post. >> Has anyone had practical experience with small commercially available time >> servers / ntp servers suitable for mobile use in a vehicle. > > I don't know about any commercially-available products, but it sounds > like it'd be pretty straightforward to do with a Raspberry Pi or > something similar if you don't mind a little bit of DIY. > > What constraints do you have on budget, size, power requirements, and cooling? > >> The use case is I am in need of an accurate (ie. within 100 ms) time source >> for several pc's in moving vehicle. Being able to run directly off a 13.8 >> or 28 VDC source would be a major plus but AC power is also available. > > The Pi runs on 5V DC. DC-DC buck converters that can convert 7-35V to > 5V DC are cheap, efficient, and widely available. Shouldn't be a > problem. > >> Hold over if there are gaps in GPS coverage is also a major plus. > > How long would you need holdover? Seconds or minutes (e.g. driving > through a tunnel)? Hours? Days? Would the computers in the vehicle be > subject to large temperature shifts? > > A Pi should be able to handle +/- 100ms of holdover in the > minutes-to-hours range using NTP. > >> We already have a GPS with a 1 pps output, but an integrated box with it's >> own GPS would be best. > > A tiny integrated module like the Adafruit Ultimate GPS breakout[1] is > cheap, handy, and emits a 1PPS signal. It's also extremely small and > can be purchased in "hat" form[2] that mounts directly to the Pi. > > Cheers! > -Pete > > [1] https://www.adafruit.com/products/746 > [2] https://www.adafruit.com/products/2324 > > -- > Pete Stephenson > > On Tue, May 12, 2015 at 7:11 PM, Mark Spencer <[email protected]> > wrote: >> Hi sorry for a possibly OT post. >> Has anyone had practical experience with small commercially available time >> servers / ntp servers suitable for mobile use in a vehicle. >> >> The use case is I am in need of an accurate (ie. within 100 ms) time source >> for several pc's in moving vehicle. Being able to run directly off a 13.8 >> or 28 VDC source would be a major plus but AC power is also available. >> >> Hold over if there are gaps in GPS coverage is also a major plus. >> >> We already have a GPS with a 1 pps output, but an integrated box with it's >> own GPS would be best. >> >> Yes I am aware I could feed a 1 pps signal into a laptop and use that as a >> time server and I may end up going that route. >> >> There is a small Ethernet LAN in the vehicle. The pc's currently get their >> time via a wireless connection to various NTP servers. I need to be able >> to ensure accurate time on the PC's if there is no wireless coverage. >> >> >> This is for a one off project so piecing together various parts is an option >> but a single box COTS solution would be nice. I've found a few candidates >> via web searches but would welcome any feed back. >> >> Thanks in advance >> >> Mark Spencer >> _______________________________________________ >> 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. > > > > -- > Pete Stephenson > _______________________________________________ > 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.
