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EEVblog => EEVblog Specific => Topic started by: EEVblog on February 15, 2013, 10:13:10 pm

Title: EEVBlog #425 - Mailbag
Post by: EEVblog on February 15, 2013, 10:13:10 pm
EEVBlog #425 - Mailbag (http://www.youtube.com/watch?v=ifQjQa0ZxCc#ws)

Dave.


Title: Re: EEVBlog #425 - Mailbag
Post by: LEECH666 on February 15, 2013, 10:46:20 pm
I think the swedish post stamp showed rendeers and the three biblical Magi - Caspar, Melchior and Balthasar. Based on that my second guess is, that this is some kind of Christmas themed post stamp.

Cheers,
Florian
Title: Re: EEVBlog #425 - Mailbag
Post by: Len on February 16, 2013, 04:04:57 am
The Canadian stamp is for the Year of the Snake.
http://www.canadapost.ca/cpo/mc/personal/collecting/stamps/2013/2013_jan_year_of_snake.jsf (http://www.canadapost.ca/cpo/mc/personal/collecting/stamps/2013/2013_jan_year_of_snake.jsf)
Title: Re: EEVBlog #425 - Mailbag
Post by: LEECH666 on February 16, 2013, 07:34:36 am
Sorry, but that snake stamp looks like a snake with a ball sack / scrotum atop of it's head to me. *chuckles*

Cheers,
Florian
Title: Re: EEVBlog #425 - Mailbag
Post by: Herr R aus B on February 16, 2013, 09:45:12 am
The pacemakers might also come in handy next time Dave rants on proprietary designed power plugs and stuff :-)

Regards

Axel
Title: Re: EEVBlog #425 - Mailbag
Post by: NiHaoMike on February 16, 2013, 12:28:51 pm
As for the timer, the US versions are built the same way, just with a different plug/socket, a different gear ratio (due to the 50/60Hz difference), and a different dropping resistor.
BTW, while the power loss in the resistor is pretty small, it adds up if you have a bunch of those timers around the house. Replacing the resistor with an X rated capacitor (calculate for the same impedance and measure the current, actual value used will be lower since the motor is inductive) will greatly cut losses.
Title: Re: EEVBlog #425 - Mailbag
Post by: bitwelder on February 16, 2013, 07:40:04 pm
I think the swedish post stamp showed rendeers and the three biblical Magi - Caspar, Melchior and Balthasar. Based on that my second guess is, that this is some kind of Christmas themed post stamp.
You're a little off with the guess...  ;D
The Finnish stamp has reindeers but the three figures are actually the daughters of the Mother Goddess of Childbirth from the Sami shamanic religion (Sami are indigenous population living mostly in the northern Scandinavia).
A series of 4 post stamps has been released to celebrate the opening of a Sami cultural center.
Here is a picture of the whole sheet (which is shaped like a shamanic drum skin): http://3.bp.blogspot.com/-NjvqeoTfR9A/T6VGaOQXaSI/AAAAAAAAIwc/U3gLnjmIpow/s1600/Finnland+Kulturzentrum+Sajos.jpg (http://3.bp.blogspot.com/-NjvqeoTfR9A/T6VGaOQXaSI/AAAAAAAAIwc/U3gLnjmIpow/s1600/Finnland+Kulturzentrum+Sajos.jpg)
Title: Re: EEVBlog #425 - Mailbag
Post by: adam1213 on February 16, 2013, 11:21:56 pm
In regards to the camera shown in the video:

I wonder why they used a non standard charger plug for the camera.

I don't know the specs for the camera / battery but based on http://store.jvc.com/product.asp?Model=BN-VG138US (http://store.jvc.com/product.asp?Model=BN-VG138US) 
capacity: 3.6V, 3750mAh.  charging from standard USB instead would likely take 3-8 hours which may be acceptable.  I wonder why they chose the non standard charger.
Title: Re: EEVBlog #425 - Mailbag
Post by: Winston on February 17, 2013, 03:36:24 am
A way to get through your backlog of mail would be to open it up off-camera, select the coolest stuff to cover and then talk about it in the mailbag segment, covering it further in a tear-down segment if it merits it. Frankly, I've never wondered was was inside of an outlet timer being pretty sure I'd find exactly what you found.
Title: Re: EEVBlog #425 - Mailbag
Post by: opablo on February 17, 2013, 07:17:40 am
Does anybody know how precise are the Mains 50/60Hz ?

I know that some old microwave ovens were also using them to track time...

How does that precision compares with an RTC chip with a 32.768KHz crystal ?
Title: Re: EEVBlog #425 - Mailbag
Post by: grumpydoc on February 17, 2013, 07:33:30 am
The spring loaded shutter which blocks access to the live & neutral until the earth pin is inserted is nothing special - that's how UK sockets work and so they have to do it that way.

Quote
Does anybody know how precise are the Mains 50/60Hz ?

Over long periods I think it's fairly stable - mains driven digital clocks used to use it as the reference frequency. Over short periods it does go up and down quite a lot. I'm afraid I don't have a reference to how accurate handy but I'm sure google can come up with something.
Title: Re: EEVBlog #425 - Mailbag
Post by: Bored@Work on February 17, 2013, 08:28:36 am
The spring loaded shutter which blocks access to the live & neutral until the earth pin is inserted is nothing special - that's how UK sockets work and so they have to do it that way.

Quote
Does anybody know how precise are the Mains 50/60Hz ?

Over long periods I think it's fairly stable - mains driven digital clocks used to use it as the reference frequency. Over short periods it does go up and down quite a lot. I'm afraid I don't have a reference to how accurate handy but I'm sure google can come up with something.

http://www.mainsfrequency.com/ (http://www.mainsfrequency.com/) has some information and a live display.
Title: Re: EEVBlog #425 - Mailbag
Post by: c4757p on February 17, 2013, 08:34:09 am
Over long periods I think it's fairly stable - mains driven digital clocks used to use it as the reference frequency.

Not just "used to" - I have an alarm clock bought this year that uses mains frequency. Companies are still cheap enough not to buy watch crystals. (The annoying part is that this means the best frequency reference it has when running off the backup battery, as far as I can tell, is an RC oscillator. It is five minutes fast after being unplugged for ten minutes...)
Title: Re: EEVBlog #425 - Mailbag
Post by: Ferroto on February 18, 2013, 12:53:58 am
I once got a cheap Chinese mp3 player for Christmas and the 12v plug pack used a Male 3.5mm audio jack. It was possible to plug 12 volts directly into the headphone jack.
Title: Re: EEVBlog #425 - Mailbag
Post by: SeanB on February 18, 2013, 01:42:08 am
The annoying part is that this means the best frequency reference it has when running off the backup battery, as far as I can tell, is an RC oscillator. It is five minutes fast after being unplugged for ten minutes...

I have the same chipset clock, and opened it up and looked up the NMOS chip inside, then looded at the RC clock backup and adjusted it to run slow. Much better to have a few minutes behind in a power cut as it is a lot easier to go forward rather than going all the way around the minutes when the power is back. Luckily mine had a trimpot for this.

At the same time I removed half the board with the radio side and shoehorned an OPTO22 hockey puck SSR inside to control the bedside light. I do not need a heatsink on this 20A unit when it is running a 32 candlepower lamp.
Title: Re: EEVBlog #425 - Mailbag
Post by: c4757p on February 18, 2013, 02:42:22 am
I would rather it run fast. If the power is temporarily lost at night, it will wake me early, not late.
Title: Re: EEVBlog #425 - Mailbag
Post by: SeanB on February 18, 2013, 05:00:12 am
You adjust it till it only loses a minute an hour....
Title: Re: EEVBlog #425 - Mailbag
Post by: c4757p on February 18, 2013, 05:10:50 am
Mine didn't have a trimpot (I'm sure that's why it was off so much to begin with) and I really didn't want to spend time modifying a $5 alarm clock. (In the five years I've been in this house we have only lost power once, so it's not a big deal. I'd just use a different clock if it really mattered.)
Title: Re: EEVBlog #425 - Mailbag
Post by: tom66 on February 20, 2013, 07:26:03 am
Our plugs in the UK are well designed: that shutter is a legal requirement, and directly inhibits attempts to access mains power using e.g. a screwdriver. (You need at least two...)
Title: Re: EEVBlog #425 - Mailbag
Post by: alanb on February 21, 2013, 01:26:49 am
Quote
Quote from: grumpydoc on February 16, 2013, 08:33:30 PM

Over long periods I think it's fairly stable - mains driven digital clocks used to use it as the reference frequency.


Not just "used to" - I have an alarm clock bought this year that uses mains frequency. Companies are still cheap enough not to buy watch crystals. (The annoying part is that this means the best frequency reference it has when running off the backup battery, as far as I can tell, is an RC oscillator. It is five minutes fast after being unplugged for ten minutes...)

In the UK the short term accuracy is within +- 1%. This is a legal requirement of the licence granted to the National Grid. If it looks as if the frequency is falling outside that limit they either bring more capacity on line or shed some of the load.

Title: Re: EEVBlog #425 - Mailbag
Post by: robbak on February 21, 2013, 03:31:04 pm
Does anybody know how precise are the Mains 50/60Hz ?

I know that some old microwave ovens were also using them to track time...

How does that precision compares with an RTC chip with a 32.768KHz crystal ?

In the short term, as others have stated, it varies quite a bit. But in the medium term, they actually cycle count, compare it with UTC standard, and adjust. So, long term and baring blackouts, a  mains synced clock will never drift.