Relay circuit module

Circuits are somewhat like programming, sometimes you use ready made functions when you program.

It is useful to have some basic circuit modules around you in case you need to test something or want to work on your next robot and don't need to create everything from scratch. In this article or tutorial, I'll share with you making a 12V relay circuit module.

A relay circuit is used to control (switch on/off) AC or DC voltage line without affecting your micro-controller (Arduino, Raspberry Pi, PIC, AVR...etc.) or digital control unit, at least when done right :)!

When you toggle the voltage on a relay coil, it works as a mechanical switch, moving a metal arm/contact from one node to the other, literally switching on or off. Read more about relays here


I started drawing the circuit using Eagle PCB design software, there is a free version for personal use here Eagle Express.

Schematic:

PCB:

Once you have the PCB design ready, you want to print and transfer the printed lines on a PCB to create your circuit. You can probably mount the components on one of the ready made projects PCBs, but I thought I'd make my own for the fun of it.

To create your own PCB you can check out this guide, I will also share my own experience here. The secret to transfer the printed ink routes to a copper surface lies in three things: 

1. The ink
2. Paper type
3. and heat! 

You need a laser printer, and with the right paper type, you can use an iron to transfer the ink to the copper surface. The best paper type is magazine paper! I didn't believe that at first, but I tried it and it got me great results.

You might think that the text on the magazine paper will interfere, but it won't. Here is the one I printed. I probably should have avoided printing on the black photo part though!

Also here is the copper PCB I will cut to fit the design.

PCB cut to the proper dimensions, needs to be cleaned up :)

To clean up the PCB from the copper oxide layer and dirt. I just use some steel wool and running warm water, and it's all ready and shining :)

I also cut around the printed PCB and remove the excess paper, looks like they should fit :)

Checking that all printed circuit lines are within border of the cut PCB... all good

Now that we printed the PCB on paper, we need to start transferring the ink to the copper PCB. This is where we need heat. I have had good results using an iron. But someone suggested that you can use a laminating device, so I bought one from a local store to see how it'll work.

That's the one I found:

I opened it up to clear way for the PCB (PCBs are thicker than the lamination) 

CAUTION: this is 220V main voltage!! If you are using this method and your laminator needs to be opened to clear way too, be EXTREMELY CAREFUL, I will not be held liable nor responsible if you electrocute yourself! If in doubt, don't.

I like to pre-heat the PCB, so I give it a few runs into the laminator, be careful it will become very hot

Now let's tape the printed paper to the PCB board to make sure it doesn't move when it is heated and moving through the laminator's rolling presses. I use paper tape, I don't use normal tape to avoid that it may heat up and melt and ruin the rolling presses!

Align them, use paper tape on one side, then make sure they still align :)

Once aligned, secure it with more paper tape

Time to run it through the laminator quite a few times... After a while of applying heat (be careful it will be very HOT!) you will start to see through the paper and the printed lines will become more apparent through the paper.

You will need to experiment how many passes are enough (even if you are using an iron). When you are satisfied, handle the PCB with care, as it will be hot (I can't stress this enough!). 

Once done prepare a warm water and soap bath for the PCB and leave it there for a while for two reasons: 

1. To cool down
2. To make it easier to peal the paper off (after all that heat, the printed paper and the paper tape sticks to the board quite well)

After a while you will be able to remove the paper tape

The paper can be pealed off with your hands, ink seems to have transferred well..

Make sure you remove all the paper and tape residues, until you are left with a really good transfer of ink only on the PCB. Looking good..

Now is the time you put the PCB in the etching solution, this solution will eat away the copper on the PCB except for the parts under the ink (protected by the ink). Leave it there for a while but keep it monitored. If you leave it too much, the etchant will eat the copper under the ink.

 After a while you should be able to see the exposed copper parts of the PCB disappearing..

Eventually all the exposed copper will disappear, get the PCB out (preferably not with your hands!) use insulating gloves or a tool to grab the PCB and rinse thoroughly

Once done, you should end up with a clean PCB with only the printed tracks remaining

Use Thinner or Acetone to remove the ink, or even steel wool (but be gentle, you don't want to remove the copper tracks)

Time to drill the holes, Dremel tool is a great way to do that

All done and ready for the components

We mount the components one by one (sorry for the low quality photos!)

Solder everything..

And test...let there be light :)

This 12v relay module can be useful to control a DC motor or switch on a high AC voltage. You will find many tutorials about relays in robotics or home automation. This can serve as a quick module to test before you create. 

Hope this was somehow useful to you,

Have a nice day,