Cognoscis

I think this is a redundant topic. But what the hell, cyberspace is being wasted on useless subjects, so repetition of something useful wouldn’t hurt. Breadboards are the best way to learn or test a circuit. Then, you want to make a more permanent circuit, so you go for one of those general purpose PCBs. I dont have anything against the general purpose PCBs, but as the circuit becomes more complex, you become entangled in a mess of wires that can drive you crazy. Completely nuts. Debugging the circuit will become very difficult, irritating and time consuming. To give you some example just look at the pictures below. The breadboard has a circuit to generate 38 kHz IR signal for modulated IR sensor explained in my previous post. The second picture is a part of LDR sensors I made for my line follower robot. The picture has a comparator circuit and a motor driver circuit and you can see the mess the wires have made. It still has the LEDs and the LDRs going around the robot. The best way to eliminate this mess is to make your own PCB so that you can eliminate the wires and make really compact connectors from one board to another. So, lets see how this process goes

IR Tx on breadboard

General purpose PCB mess

First of all, you need to design the circuit to draw on the copper clad plate. I personally feel that ExpressPCB is good enough for this purpose. Lets face it, even though there is an option for double side design, we hardly use it. Soldering SMDs is a bit more complicated so a single side design is more than enough even for moderately complicated circuits. You can freely download the software from here and use it to design the circuits. The software has both a schematic and PCB designer. You can make a schematic in ExpressSCH and generate a netlist and then import this to the ExpressPCB to generate a PCB design. But I think its better to design the PCB ourselves so that we can optimize it better. Few tips to help you make better designs

• Keep the connecting paths about 1 mm so that they remain intact when handled roughly.
• Use as less space a possible. This is one of the prime reasons we make PCBs in the first place
• Start designing with the copper in top layer and make the PCB in the normal way. After it is completed, transfer it to the bottom layer to obtain the mirror image of the circuit.
• After you design the entire circuit, you will be left with a lot of empty space. Fill as much of this space as possible and connect that huge area to the ground point and/or the Vcc. There is also an option to just fill the empty space without connecting it to anything else. This is done to reduce the amount of Copper that needs to be etched. Less the amount, faster the etching process will be. Also you will save the etching agent. An example circuit is shown below. Its for 4 modulated IR transmitters with its own power supply and switch

IR PCB

Once you have your PCB design, you can print out that circuit. Make sure it is inverted (Mirror image) as you can see in the picture above. After the circuit design, there are two processes that can be followed. In this post I will describe the one with the iron box. For this process, we need to get the print out of the circuit on a paper. Glossy paper is preferred, but even normal white paper will do. The most important thing is that the printer must be a LASER printer. This is vital because, we will transfer the ink on the paper to the copper-clad plate. To transfer the circuit, follow these steps

• First, properly clean the copper surface so that there is no dust or any other impurity and completely dry it.
• Carefully place the circuit on the copper and place a hot iron box on top of it. As soon as you do this, the paper will stick to the copper.
• Keep ironing the paper for about 10 min. Dont be in a rush, let it take its time. After about 10 min, gently peel off the paper. If done properly, the circuit diagram will have transferred onto the copper plate.
• Use a black marker to fill out any places where there is little ink. You may also want to draw the lines that look dim. Be careful near the holes. The finished product will look somewhat like in the picture below

dirty copper clad plate. Needs to be cleaned

Circuit transferred onto copper plate

After transferring the circuit you need to remove the excess copper from the plate. This process is called etching and we will use Ferric Chloride as the etching agent. Its easily available salt and should be carefully handled as it is very corrosive. Keep all the good dishes away from it and use some old plastic trough. Make a solution of ferric chloride in the trough. The concentration of the solution need not be precise. Just mix the salt in little amount of water till the solution becomes opaque and reddish brown (colour of rust). Dont use a lot of water, it will be just waste of the salt. If possible, warm the solution a bit. This is not necessary, but it will speed up the process. Dont heat it, just warm it. Then insert the Copper plate into the solution and eep stirring it. Normally it will take about half an hour for the copper to come off. Be patient and keep stirring, it will speed up the process. After the copper is etched, you will get a PCB something like the one shown below

After etching and drilling

After the etching is done, we need to drill the holes to place components. I used 0.8 mm drill bits to make the holes. The above picture was my first attempt and you can see that I have messed it up. But, its really not that difficult. You may need one or two practise rounds. But, you need to be really careful when drilling the holes belonging to ICs. The holes must lie in a straight line else you will have a really hard time placing the IC. Trust me, I know from experience. Now, these drill bits are definitely available in the hardware shops, but a bit difficult to find. If you live in Bangalore, then you can definitely find it in SP road. Thats where I bought them. You cannot use 1 mm drill bit, it will be VERY big. You can see the hole above C3 in the PCB. Thats from 1 mm drill bit. Use 0.8 mm, its optimum. To get an idea, below is the picture of those bits and to compare, I have place a 0.5 mm lead between them.Also, I used these bits with the normal heavy duty Drilling machine without any problem. They will fit correctly and be careful as they can break if not handled carefully

0.8 mm Drill bit with 0.5 mm lead in the middle

With the drilling, you have now come to the final stage. Not it is soldering time. You can follow my soldering guide to solder the circuit elements. Always use IC holders in the circuit. The finished product will look as shown in pictures below. I have not soldered everything, but you can see how neat and organized the circuit is. This circuit holds 4 modulated IR transmitters along with its own power regulator.

Soldered PCB (Bottom Surface)

Soldered PCB (Top surface)

I really apologise as all the snaps are not of the same PCB. I did not take any snaps during the maing of the last one. So, I had to use the older pics. But it gives you the idea of each and every step. Please feel free to share anything other than what I have put up and please do ask for any clarifications.

There is one more process; the one using UV light. I have not yet tried it. I think I will try it and share the outcome