Fantastic, the NPL’s Internet Time Service (ITS) User Guide seems to have the details on what’s needed for use with the NTP libraries used.
I appreciate what you’re saying about power consumption.
Their 60kHz radio clock, I hadn’t twigged you’d meant this radio-controlled clock, we’d need some extra hardware to pick that up. Could be a ‘module’ add-on feature.
Another low-power option would be to use the rfm69 module to receive a packet of time information from the ‘hub’.
edit: the NTP libraries seem to use server default pool.ntp.org.
Looking up pool.ntp.org
(or 0.pool.ntp.org
, 1.pool.ntp.org
, etc) will usually return IP addresses for servers in or close to your country. For most users this will give the best results.
. pool.ntp.org: How do I setup NTP to use the pool?
@Robert.Wall are you contented with the use of internet time from the ‘hub’ and a radio packet sent to the node, with some kind of correction algorithm implementation outlined above?
Seperate subject. I did some testing yesterday on the stm32 proto board we received earlier this year. Specifically, testing the accuracy of VT and CT inputs, and checking the channels for noise. A problem was apparent straight away, with unusually high CT channel readings, and high VT channel readings while the VT was disconnected.
Using the scope I found the problem at the stm32 analog reference input (VREF+), upstream the MCP1501 0.1% reference voltage had too much capacitance on it’s output, causing an oscillation at 16kHz 400mV peak to peak.
I removed the capacitance and everything became stable. Looking at the MCP1501 datasheet the reasons are clear.
Next, I spit out the ADC readings of the BIAS and it was doing something interesting. It was bang on set on a single ADC value of 1984 (a bit low for some reason), EXCEPT, for occasional dips for a single value at a time (every few milliseconds) down to about 1970. The next ADC sample it’d be back up to 1984. This is something to revisit and check in a different context, and with a different voltage reference IC.
AN2834 for the stm32 shows capacitors connected to VREF+, but in the context of the MCP1501 that amount of capacitance wasn’t appropriate. Looking again at AN2834 I noticed the suggestion of using a diode as a reference voltage, something like a LM236.
Any other recommendations welcome. I’ve ordered a LM236 to test. I’m interested in finding a fairly bomb proof 0.1% reference. Just to make clear the reasons why, we need to know the volts per adc division.
. https://github.com/openenergymonitor/STM32/blob/master/Emon3CT_CB/Src/main.c#L177
Noticing another interesting one here: https://uk.rs-online.com/web/p/voltage-references/1000664/
It’ll come down to cost too. How much are we willing to spend on eliminating about 0.9% error? Users here have posted a few times about accuracy, so it’d be nice to nail something good out-of-the-box.