[time-nuts] RasberryPi, timing and GPS receivers

k6rtm at comcast.net k6rtm at comcast.net
Tue Oct 16 18:27:16 EDT 2012

I've been looking at the Raspberry Pi for a number of projects as well, and have been running one for a few weeks. 

My take on the early stability concerns/complaints are that the majority of those are due to poor power supplies, with some assistance from the Raspberry Pi design. 

Measure what you have for DC at TP1 and TP2; it should be close to 5 volts. 

The polyswitch self-resetting fuse on the power input introduces series resistance (in the wrong place); on my unit it measures 0.36 ohms (4-wire measurement with my HP33401A). Couple this with a cheepie USB supply that's already below 5 volts, and you're on thin ice. Do anything that spikes power consumption, such as Ethernet, GPU, or plugging in USB devices, and you generate more of an IR drop across the polyswitch which can cause erratic operation or resets. 

Use a good power supply -- 5 volts at an amp. Adafruit sells one that's 5V/2A for under $10. 

Or you can bypass some of the protection components and connect your +5 supply to TP1 and TP2. 

Running mine from a solid power source the only problems I've had are with my own crummy code... 

Bob K6RTM 


Message: 5 
Date: Tue, 16 Oct 2012 15:06:19 -0600 
From: xaos at darksmile.net 
To: Discussion of precise time and frequency measurement 
<time-nuts at febo.com> 
Subject: [time-nuts] RasberryPi, timing and GPS receivers 
Message-ID: <20121016150619.16306sbpxvjy88qz at darksmile.net> 
Content-Type: text/plain; charset=ISO-8859-1; DelSp="Yes"; 

Hello everyone, 

I started a new project for myself where I would use the RasperryPi 
Linux board 
as a NTP server. 

My goal is to design a custom board for the Pi and mount a GPS 
receiver on it. With this combination, I should be able to configure 
NTP for the Pi and thus have the Pi act as a Stratum 1 NTP server. 

The new RasberryPI has 512MB memory so it should be fine for running 
just ntpd. 

Question: What GPS timing module should I go with? No more Motorola 
Oncore so what's best right now? Who sell modules? What are the price 

Your comments are most welcome. 

-George, N2FGX 

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