Friday, July 13, 2018

Incandescent vs Fluorescent vs LED


Estimated lifetime: For LED light you will often see ridiculous amount like 50,000 hours or so, but in reality those are not marketing gimmick. What manufacturers do is push more than normal current to produce a certain output power which reduces the lamp life significantly.

Friday, July 6, 2018

ঢাকার বাইজি উপাখ্যান

I will be blatantly honest here, this book is Rubbish. First of all let us look at the format, it comprises short stories written by many authors, editor here did nothing, he just copied and pasted the whole thing, didn't even care that the same information is there like 5/6 times.

For example let's look at the story of "1200 Kanchonis and their 80k cost" it came in page numbers 37, 85, 104, 117, 129 and 132. That much repetition in a single book shouldn't be allowed and it is not the only occurrence either.

The story about "Bibekanondo addressing a dancer as Mother" was in page 76, 79, 91 and 135. I mean what was the editor doing? Just increasing page count so that he can make some money? Is that all there to it?

Not to mention the amount of spelling mistakes in there, it is staggering

Overall not a book anyone should buy, any other old stories about Dhaka city would have been a better book than this one to get the same information.

Thursday, June 28, 2018

FAQ-6 Can Rechargeable and non-rechargeable cells be Mixed together?

They can be but it is highly inadvisable to do so.

There are many different types of Rechargeable and non-rechargeable cells so talking about all of them will not be possible in here but let me give you some ideas. If you have a device that takes multiple cells series, say an Infrared Remote controller for TV you might be okay with putting two types together but remember rechargeable NiMH has lower terminal voltage compared to non-rechargeable Zinc-Carbon/Zinc-Chloride/Alkaline cells, so the rechargeable one might get flat sooner and charged at reverse polarity which is not good for it plus Infrared remote controllers takes so little power there is not reason to use NiMH in them.

The process mentioned earlier will take a moderate amount of time to happen if it happen but if you have a device that has parallel cells, like the wall clock I have in my room, it requires 3 AA cells in parallel for it’s chime and in this case adding a NiMH with Alkaline might be catastrophic as the Alkaline with it’s higher terminal voltage trying to charge the NiMH.

In short not a good idea to do such a thing. 

Monday, June 25, 2018

FAQ-5 Does New Cell Phone Require 10 Hours of charge?

They Don't. 

The idea of charging for 8 hours came from the NiMH and SLA/LA type batteries. Lithium batteries charge at a much faster rate and 8 hours of charge might even stress it them a little(if it is charged at normal rate).

Here is the thing both NiMH and SLA are usually charged at a much lower rate, even at 1/10th(0.1C) of capacity so they often require 10+ hours of charge to be fully topped up. On the other hand Lithium batteries are charged at 1/2th(0.5C) of capacity to even more than 1C so they do charge up pretty fast.

The reason why new phones are to be charged is to simply have good capacity out of it, they often shipped at 40–60% capacity and during the time at inventory they goes down a bit so if you want to use it you have to charge it up to 100% and you are good to go. Time is not that important. If you think about a 20000mAh power bank and charge it at 1A, you will need 20+ hours of charge and it will be fine for it but if you have a phone and charge it for that long it might have small negative impact on the battery.

Monday, May 14, 2018

Simple 12V Lamp Blinker

This blinker that I'm going to show right now can be used in automotive application or any other application that is suitable. As the title suggests it is going to be a very simple diagram with minimum component count.

Component list:

1 12V Relay

1 220µF 35V

1 220Ω 1W 

12V 5-21W 


Working Principle

The circuit itself is very simple. When the power is turned on the 220µF capacitor starts to charge via the 220Ω Resistor. As soon as the voltage reaches the working voltage of the relay it turns on. When it turns on it completes another path of a very low resistance through which required amount of current passes to the Lamp to light up. But that depletes the capacitor completely and relay stops again. As the relay stops the Lamp extinguishes and the capacitor starts to charge up again and the whole process repeats.


Increasing the value of the Resistor and the capacitor will increase the time it takes to charge up the capacitor which will lower the blinking frequency.

Make sure to use a relay that can handle the amount of current required for the lamp.

Wednesday, May 2, 2018

Powering up SBC - The Right Way

As with the rise of IoT and interesting little projects single board computers are becoming more and more popular. With each iteration they are getting more powerful as well which makes it imperative to have a good quality stable power supply. You can have everything okay with your project but a bad power supply can make things go sour and that power supply can make it difficult to troubleshoot as well. If you measure, even if it is not a good quality USB power supply you might see something like 5V and that can give you the false impression that the power supply is okay. It might be okay but as soon as you load it up it might not stay stable at 5V which is required for many of this single board computers to run.

The Power Source

In the early time for SBC they didn't have much on them so 1.5A of current was more than enough even I ran my RPi 2 with 1.35A just fine, with a single USB flash storage device connected but as time goes on more and more things are added to the board itself. Now RPi has built in 5GHz Wi-Fi and Gigabit Ethernet. So that 1.35A power source is no longer suitable. Furthermore if you add mechanical storage, say a portable Hard drive, that drive alone will consume around 1A, so in that case either you have to provide around 2.5A to the board or use a powered USB Hub. The latter one is the better solution. Don't just try to run it on a 1A charger of questionable built that was lying on the floor for couple years.

The Cable

So you have a good power source yet you are having issue with it, why! Well a good quality power supply is not everything, you have to deliver that power to the device properly, so a good quality wire is also as important as the power supply itself. As not all cable will be able to carry high current without dropping too much voltage. Many of the cheap cables that are available in the market can be good up to 0.5-1A but try pulling more voltage will go down to unstable region. Cable length is also important, longer the cable is usually higher the resistance is so more voltage will be dropped across it. Also the connectors are important, a tight and secure connection is necessary for delivering stable power. If the connectors move too much the board might not run properly.

How much is enough! 

Then how much power is enough? Well depends on your project and the board itself. Refer to the product manual or website to know the recommended power for it. Add more device and add more to it. For example if a board needs 1A to run by itself and you add one portable HDD and a pair of mouse keyboard, you need to provide a total of 2.5A to make it work properly. You will be needing a cable that can deliver that much power as well. Yes I'm saying power but stating current but you should know what I'm talking about. 2.5A at 5V is almost 12.5W.

A few words on RPi

If you plan to run multiple devices from a RPi USB ports directly do keep in mind that all 4 of them will provide 1.2A total. So make sure you don't try to run a pair of portable HDD directly on them as even you plug in a 4-5A power source, they won't run properly. Again like I said above use a powered USB Hub. If you see the RED LED is getting extinguished and coming back again or on the display(if one is connected) a power icon on the top right is seen that is the indication that RPi is not getting enough power.