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:

Relay
1 12V Relay

Capacitor
1 220µF 35V

Resistor
1 220Ω 1W 

Lamp
12V 5-21W 

Diagram:


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.

Note:

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.