etbe - Russell Coker

Voltage Inside a Car

etbe — Fri, 17 May 2013 02:57:47 +0000

I previously wrote a post with some calculations about the power supplied to laptops from a car battery [1]. A comment on the post suggested that I might have made a mistake in testing the Voltage because leaving the door open (and thus the internal lights on) will cause a Voltage drop.

So I’ve done some more tests:

Test	Voltage
battery terminals	12.69
front power socket with doors closed	12.64
front power socket with doors open OR ignition switch on	12.37
cigarette lighter socket with ignition switch on	12.32
front power socket with doors closed and headlights on	11.96
front power socket with engine running	14.38
front power socket with engine running and headlights on	14.29

In my previous tests I recorded 12.85V inside my car (from the front power socket which although having the same connector as a cigarette lighter isn’t designed for lighting cigarettes) and 13.02V from the battery terminals – a 0.17V difference. In my tests today I was unable to reproduce that but I think that my biggest mistake was to take the reading too quickly. Today I noticed that it took up to a minute for the Voltage to stabilise after opening a door (the Voltage dips after any current draw and takes time to recover) so a quick reading isn’t going to be accurate.

My car is a Kia Carnival which has two sockets in the front for power and for actually lighting cigarettes. The one for lighting cigarettes has a slightly lower Voltage and only works when the ignition is turned on. The car also has a power socket in the boot (the trunk for US readers) which delivers the same Voltage as the power socket in the front.

Also one thing to note is that today is a reasonably cold day (16.5C outside right now) and my car hasn’t been driven since last night so the battery would be quite cold (maybe 12C or less). My previous measurements were taken in summer so the battery would have been a lot warmer and therefore working more effectively.

Conclusion

The Voltage drop from turning on the internal lights surprised me, I had expected that a car battery which is designed to supply high current wouldn’t be affected by such things. Certainly not to give a 2% Voltage drop! The Voltage difference from reading inside the car and at the battery terminals might be partly due to the apparent lead coating on the terminals, I pushed the probes of my multimeter beneath the surface of the metal and got a really good connection.

The 14% Voltage increase when the engine was running was also a surprise. It seems to me that if you are running a power hungry device (such as a laptop) it would be a good idea to disconnect it when the engine is turned off. A 14% higher voltage will give a 14% lower current if the PSU is efficient and therefore less problems with heat in the wiring and less risk of blowing a fuse.

Also it’s a good idea to be more methodical about performing tests than I was before my last post. There are lots of other tests I could run (such as testing after the engine has been running for a while) but at the moment I don’t have enough interest in this topic to do more tests. Please leave a comment if there’s something interesting that you think I missed.

[1] http://etbe.coker.com.au/2013/01/24/power-supplies-wires/

Effective Conference Calls

etbe — Fri, 17 May 2013 01:53:47 +0000

I’ve been part of many conference calls for work and found them seriously lacking. Firstly there’s a lack of control over the call, so when someone does something stupid like putting an unmuted phone handset near a noise source there’s no way to discover who did it and disconnect them.

Another problem is that of noise on the line when some people don’t mute their phones, which is related to the lack of control as it’s impossible to determine who isn’t muting their phone.

Possibly the biggest problem is how to determine who gets to speak next. When group discussions take place in person non-verbal methods are used to determine who gets to speak next. With a regular phone call (two people) something like the CSMACD algorithm for network packets works well. But when there are 8+ people involved it becomes time consuming to resolve issues of who speaks next even when there are no debates. This is more difficult for multinational calls which can have a signal round trip time of 700ms or more.

I think that we need a VOIP based conference call system for smart phones to manage this. I think that an ideal system would be based on the push to talk concept with software control that only allows one phone to transmit at a time. If someone else is speaking and you want to say something then you would push a button to indicate your desire but your microphone wouldn’t go live while the other person was speaking. The person speaking would be notified of your request and one of the following things would happen:

You are added to the queue of people wishing to speak. When the other person finished speaking the next person in the queue gets a turn.
You are added to the queue and the moderator of the call chooses who gets to speak next. This isn’t what I’d prefer but would probably be desired by managers for corporate calls.
You get to interrupt the person who’s speaking. This may not be ideal but is similar to what currently happens.

Did I miss any obvious ways for the system to react to a talk request?

Is there any free software to do something like this? A quick search of the Google Play store didn’t find anything that seems to match.

Geographic Sorting – Lessons to Learn from Ingress

etbe — Sat, 11 May 2013 13:38:04 +0000

I’ve recently been spending a bit of my spare time playing Ingress (see the Wikipedia page if you haven’t heard of it). A quick summary is that Ingress is an Android phone game that involves geo-location of “portals” that you aim to control and most operations on a portal can only be performed when you are within 40 meters – so you do a lot of travelling to get to portals at various locations. One reasonably common operation that can be performed remotely is recharging a portal by using it’s key, after playing for a while you end up with a collection of keys which can be difficult to manage.

Until recently the set of portal keys was ordered alphabetically. This isn’t particularly useful given the fact that portal names are made up by random people who photograph things that they consider to be landmarks. If people tried to use a consistent geographic naming system (which was short enough to fit in large print on a phone display) then it would be really difficult to make it usable. But as joke names are accepted there’s just no benefit in having a sort by name.

A recent update to the Ingress client (the program which runs on the Android phone and is used for all game operations) changed the sort order to be by distance. This makes it really easy to see the portals which are near you (which is really useful) but also means that the order changes whenever you move – which isn’t such a good idea for use on a mobile phone. It’s quite common for Ingress players to recharge portals while on public transport. But with the new Ingress client the list order will change as you move so anyone who does recharging on a train will find the order of the list changing during the process and it’s really difficult to find items in a list which is in a different order each time you look at it.

This problem of ordering by location has a much greater scope than Ingress. One example is collections of GPS tagged photographs, it wouldn’t make any sense to mix the pictures of two different sets of holiday pictures because they were both taken in countries that are the same distance from my current location (as the current Ingress algorithm would do).

It seems to me that the best way of sorting geo-tagged items (Ingress portals, photos, etc) is to base it on the distance from a fixed point which the user can select. It could default to the user’s current location but in that case the order of the list should remain unchanged at least until the user returns to the main menu and I think it would be ideal for the order to remain unchanged until the user requests it.

I think that most Ingress players would agree with me that fixing annoying mis-features of the Ingress client such as this one would be better for the game than adding new features. While most computer games have some degree of make-work (in almost every case a computer could do things better than a person) I don’t think that finding things in a changing list should be part of the make-work.

Also it would be nice if Google released some code for doing this properly to reduce the incidence of other developers implementing the same mistakes as the Ingress developers in this regard.

Links March 2013

etbe — Sun, 31 Mar 2013 13:55:16 +0000

Russ Allbery wrote an informative post about how to determine which charities are worth donating to [1]. He has a link to another article about the charities to which he donates and concentrates on ways of analysing the effectiveness of charities. So someone who has different ideas about which types of charity are worthy of donation could still learn a lot from his post.

Adam Green wrote an interesting article for The New Yorker about Apollo Robbins who is one of the world’s best pick-pockets [2]. Apollo picks pockets as a magician to entertain people and always returns what he steals. Now he is working with neuroscientists who are devising experiments to determine why his tricks work.

Rick Falkvinge wrote an insightful article describing the way that the copyright monopoly is in direct opposition to the freedom to make contracts [3]. It’s a good rebuttal of a common argument in favor of copyright law.

Seth Godin gave an interesting TED talk about the problems with the education system, how and why it teaches conformity and little else [4]. One of his suggestions for improvement is to have students spend their evenings watching lectures by experts and class time asking questions. He also says that everything should be open book and that there is no value in memorising anything – it’s a bit of an overstatement but it’s essentially correct.

Cory Doctorow wrote an interesting article for The Guardian about positive externalities and copyright law [5]. I think that he didn’t choose the best way of framing this issue, but he makes some very interesting points anyway.

Andrew Norton wrote an interesting article about how to reduce corruption in the police force and other government agencies [6]. A large part of this is based on making them subject to the same laws as everyone else, which seems to be a radical idea.

Valerie Aurora wrote an insightful blog post about suicide [7].

Emily Oster gave an interesting TED talk about the factors that determine the spread of AIDS in Africa [8]. It’s quite different to what you probably expect.

Kogan Mobile

etbe — Tue, 05 Mar 2013 01:24:58 +0000

Kogan Mobile is the newest virtual telco in Australia [1]. They resell Telstra 3G (not NextG or LTE) and while their coverage isn’t as good as the full Telstra service it’s more than adequate for my needs as they provide 3G coverage to 97% of the population and 2G+3G coverage to 98.5%. Their coverage is probably a lot better than Three who had the worst record of network coverage in Australia yet managed to always provide coverage where I wanted it – I was a happy Three customer for more than 6 years.

Kogan’s main selling point is that they offer unlimited calls to Australian mobile phones and land-lines and unlimited SMS for a pre-paid fee of only $300 per annum ($25 per month on average). My parents have been getting unpleasantly large phone bills which have considerably more than $25 of calls to mobile phones every month so an obvious solution for them is to sign up for a Kogan mobile phone and use it for all such calls. There are other ways my parents could save money on calls (such as VOIP) but a mobile phone is easiest and offers other benefits such as running Android apps (when compared to using a non-smart phone).

6G of Data!

Kogan also offers 6G of data per month, the down-side to this is that they bill in 1MB increments per “session”. I was worried that this might be per TCP connection or something else silly but I decided to sign my parents up for it as they aren’t going to use a lot of data (they claim that they don’t want to use the Internet on their phone but I know better). I’ve done some tests on the SIM I got for my parents. For testing purposes I installed the Kogan SIM in my wife’s new Nexus 4 and had it provide Wifi net access to my phone while we were playing Ingress.

So far after 2 days which involved a reasonable amount of Ingress (I reached level 7) as well as all the usual stuff that happens in the background for two phones (checking email, news, weather, etc) Kogan considers that 177MB have been used out of the 6144MB for the month, which means that even with what is an unusual amount of traffic for us the account in question still isn’t going to use half the quota for the month. Now that 10 days have elapsed with less intense usage Kogan considers that a total of 1373MB have been used.

days	received	sent	Kogan
2	127.24	41.54	177
10	959.39	299.6	1373

Kogan also don’t seem to mention whether they bill for transmitted data. I used the 3G Watchdog app to measure the amount data transferred, the above table has the amounts of data that 3G Watchdog considers were sent and received along with the amount that is listed by the Kogan Android app. My past experience with 3G Watchdog and Virgin Mobile is that it’s usually quite accurate but has been over-reporting the data transfers recently (I think that Virgin is only billing me for downloads while 3G Watchdog counts uploads). So the relatively small difference between the 3G Watchdog report and what Kogan thinks I’ve done means that either rounding the “session” up to the nearest meg doesn’t make any significant difference (which would imply that a “session” can be a long time) or that Kogan isn’t counting uploaded data and the session rounding up only adds about 40% to the total recorded transfer.

My current plan with Virgin Mobile gives me 1.5G per month of quota, so as long as Kogan’s rounding doesn’t increase the recorded data transfer by a factor of 4 I will still be able to transfer more data with Kogan while paying less. One disadvantage of using Kogan is that I might have to tweak programs like my email program to poll less frequently to avoid excessive session charges (a program polling every 5 minutes would use up the 6G quota in 21 days if each poll counted as a session) – although current tests indicate that this won’t be necessary. But the up-side is that there are no extra fees with Kogan, they merely restrict data access – for my use and that of most people I know it’s better to have data access cut off than to receive a large bill.

The Kogan Android App

Kogan has an Android app that will give the status of your account and allow you to change the plan etc. This is quite nice but one major disadvantage is that it’s also a sales app for the Kogan online store. This is bad for the user as some aspects of what I consider the core functionality are limited (for example there’s no way to force a poll of the data usage count or determine how current the data is). But there’s an obvious advantage to Kogan in providing a way to sell their goods that is going to be used by every customer of Kogan Mobile.

The sales part of the app isn’t very functional IMHO, it doesn’t seem to have basic functionality such as sorting a list of items by price.

Benefits of Kogan

6G of data is a lot!

$300 per annum is quite cheap, anyone who makes any serious use of phones will be paying more than that in Australia.

Lack of extra fees means that there is little need to restrict net access. I can risk getting cut off near the end of the month but I can’t risk the potential for hundreds of dollars in excess fees.

The Kogan app shows me the data used so I will probably uninstall 3G Watchdog, having one less program running is a good thing.

You get a free SIM (value $5) when you buy a phone from Kogan.

Disadvantages of Kogan

They are new to the Telco business and admit that their customer service is lacking due to unexpected demand.

If you order a SIM now they state that it will arrive in April. Apparently they are deliberately delaying orders because they can’t cope with demand.

The included call quota doesn’t include international calls. While unlimited free calls in Australia is great if you make many international calls then this could end up costing you more. Other mobile telcos such as Lebara offer good deals for International calls, it could be an option to use a Lebara SIM with an old non-smart phone while using Kogan for your smart phone.

I am concerned about the lack of detail about how data is accounted. If the definition of a “session” changes then 6G could turn out not to be enough. As Kogan is reselling a Telstra service it is possible that Telstra could change the deal without Kogan being able to stop them.

Conclusion

I will move my phone and my wife’s phone to Kogan ASAP. My general idea is to sign us up for Kogan about 2 weeks apart, so if one phone runs out of the 6G data quota then the other phone can be used as a Wifi access point for 2 weeks. If the phones don’t both have their quota end at the same time then there is less chance of both phones running out during a high traffic month.

[1] https://www.koganmobile.com.au/

Serious Begging

etbe — Sat, 23 Feb 2013 13:21:13 +0000

This evening I was driving through one of the inner suburbs of Melbourne when a man flagged me down. He said that his mother was dying and he needed a taxi ride to some hospital far away and needed to borrow $200. He was saying something about his phone, I wasn’t sure if he was planning to give me his phone number so I could call him to ask for repayment or offering his phone as collateral on the loan (incidentally a well known scam is to offer a stolen phone as collateral for a loan, it’s a way of selling a locked phone that doesn’t have cables).

I’ve encountered many beggars over the years, but he was by far the most serious about it – he demonstrated the level of desperation that I’ve only previously seen documented in history books and reports from travelers who visited developing countries. I will never know if his mother was dying, there are lots of other reasons why someone might urgently need cash (most of which won’t get much sympathy).

I gave him $20 as a gift. If his story was legitimate then I gave him 10% of what he needed so he only had to find another 9 people willing to do the same. If he was lying then I can afford to lose $20. In any case I definitely wasn’t going to do what he asked and withdraw hundreds of dollars from an ATM for him. Also regardless of whether he was telling the truth I didn’t want to have him repay me, if he’s telling the truth then I’m happy to give money to him and if he’s not then I’m better off avoiding him in future. If I had $50 I would probably have given it to him, but $200 is too much.

As I drove off I looked in my rear-vision mirror and saw him running between cars on the road trying to flag someone else down. Running through moving traffic on a Saturday night is another indication of how serious he was, generally someone who’s in a good state of mind and wants a long and healthy life won’t do that.