Introduction: Basics - Drilling Holes for PCBs
I am an old man. As such, I find it very difficult to solder in tight places. My hands and fingers go where they are not meant to go and when I solder the slotted prototype boards, I tend to cause soldering shorts, and the project does not work. You can see an example of the mess I made of a strip board in the photo.
I've tried perf boards, which are the hardest ones to do, strip boards and Manhattan boards (where you glue copper clad pieces on top of a base). The easiest of these for me is the Manhattan style. But, finally, I decided to go back to my boyhood days and make my own Printed Circuit Boards (PCB). Shaky hands can solder those without much trouble.
Step 1: Introduction
For this instructable, I've chosen to concentrate on one of the problems with PCBs and that is drilling the holes. I've also chosen to show from start to finish a project I call Toothbrushing Timer. The timer consists of an ATTiny85 programmed to flash a red ready light, and then a green light 20x in 30 seconds for four cycles. If you brush the four quadrants of your mouth with this timer, you will have done the 2 minutes of teeth brushing that the dentist says you should. Of course, you can buy an electric toothbrush that does the timing for you, but that is not a DIY project. This is.
Step 2: Tools and Materials
- Dremel or Wen or generic moto-tool
- Drill bit with diameter equal to that of the perf board. 0.042" ?
- Containers for etching copper clad boards
- Arduino UNO programming set up for ATTiny85 programming
- Copper clad board for the PCB itself
- Perf board for making the drill pattern
- FeCl3 anhydrous powder or ready-mixed liquid
- Electronic components for the project. For this one:
- ATTiny85 PU20
- 2 x 220 ohm resistors
- 1 ea red LED and green LED (ultra bright)
- on-off switch
- Medicine bottle for finished product
- 2 x CR2032 coin cells with holder
CAUTION! FeCl3 water solution is very corrosive and must be handled very carefully. Do not get any in your eyes or on your skin. Dispose of waste properly.
Step 3: What's the Problem?
The first hurdle I faced with making my own PCB for an ATTiny85 chip is to drill the holes to fit the 8 pins of the chip.
The first problem is to figure out how to make the 8-pin pattern on the PCB. The second is to drill the holes once they have been laid out.
After trying to draw the pin locations free-hand, I discovered my cache of perf boards. Those holes happen to have exactly the right spacing for the chip pins. Problem solved. I just had to put one of these boards over the copper-clad board and drill the holes wherever I needed the chip.
End of Instructable. Well, not quite.
Step 4: Why Not Use This Method for the Whole Project?
It occurred to me that I could lay out the whole project on a perf board, mark the holes where I need them and drill everything at one time.
The result is shown in the accompanying picture. This one has the holes needed for mounting an ATTiny85 and using one of the ports (#0 or Pin 5). It also has the holes needed for the battery terminals on Pin 4 and Pin 8.
My toothbrushing timer uses two ports for a red and a green LED--OK, I could have used an RGB LED, but I didn't. We're on a roll.
Step 5: Two in One. Single Port and Dual Port Boards.
Being a miserly type, I found that I could lay out the hole drilling template for two projects--a single port and a dual port.
The dual port is labeled Pins #5 and #7 in the picture. It is on the right-hand side of the drill pattern template perf board. To help clarify where this project is going, I enhanced my picture with some descriptions and with pathways and symbols for the components.
Black shows the connection to the batteries and where the on-off switch should go. The bold red lines show where there is copper continuity on the board itself. In other words, the part that is not etched off of the board. The right-hand side shows one resistor on pin 5 and one on pin 7. Those in turn lead to a red LED (pin 5) and a green LED (pin 7). The negative end of the LEDs go to a common ground connected to pin 4.
The second photo shows the "raw" drill pattern. The third photo shows the drill pattern perf board with a candidate copper clad board that will become the PCB for the project. The fourth photo shows a vise holding the drill pattern over the copper clad board. And, finally, the fifth photo shows the drill itself. The drill itself is an inexpensive one I bought at Harbor Freight for about $7. The drill bit is the same diameter as the holes in the perf board.
Step 6: The Holes Are There. Draw the Pattern.
The first photo shows the copper clad with the holes. The filmy material on top is scotch tape that I used for manipulating the board in the etching solution.
After a failure or two, I discovered that my sharpie pen was not adequate to prevent etching, and I used nail polish instead. The first time I tried it, I covered the sharpie pen drawing with nail polish. That worked very well.
Now, I only use nail polish. Clear nail polish would be better, but my wife only had red. So it goes.
You will notice that the patterns of photos are not consistent in this step. They show patterns for both the single port and dual port projects. My apologies for not getting a consistent set. BTW, I use the single port board for my Mailbox Signal system. (I may write an instructable for making three or four different kinds of Mailbox Signal systems in the future. Don't hold your breath, though.)
Step 7: Making the PCB Itself.
There are many articles on how to make PCBs. I won't burden you with pictures about my efforts. I'll briefly state the steps I use, though.
- Use plastic or rubber gloves!!! Goggles are a good idea as well. A shop apron is handy.
- Mix one part FeCl3 anydrous powder with one part water. Yes, it's strong, but it works fast. Also, I use very little for a board. The board is less than 2" square. (I use less than 3 milliliters--less than a teaspoon--of solution.)
- Very handy tip that I found in another article on making PCBs. Fold a piece of duct tape to make a slight ridge that you can grab with forceps or with your gloved fingers and tape it to the back side of the PCB board. See photos.
- Drop the board into the solution.
- Wait 2-5 minutes and check to see that the exposed copper is gone.
- When the copper is gone, rinse the PCB in plain water. Use paper towels to dry it.
The finished board looks something like the photo. OK. I'm not an artist. It's crude, but it works. Yes, it works!
All of the exposed copper is gone, and only the conducting parts are there.
Next is to solder the components. The second photo shows the soldered side. It's easy for my elderly fingers to do this job. Very easy.
Step 8: Put It All Together.
Soldering is simple.
I use one 220 ohm resistor on pin #5 and one on pin #7. The positive side of the red LED is connected to the resistor on pin #5 and the positive side of the green LED is connected to the resistor on pin #7.
The negative sides of both LEDs are connected to one pole of the switch and the other pole is connected to the negative terminal of the battery.
In the photo, you can see that I used yellow wires for the switch, a red wire for the positive terminal, and a black wire for the ground terminal of the battery.
The schematic is provided with this step.
Step 9: Program for the ATTiny85
Here I won't go into any detail about programming an ATTiny85 except to provide a reference on how to do it. This is my goto reference for programming the ATTiny85: http://highlowtech.org/?p=1695
I've done a lot of these and use an Arduino UNO as the programmer. I also used the Arduino Nano for that purpose. I've provided the program that I use for this project here.
Step 10: The End.
These photos show the finished project. The board itself and the container that I put it in.
For your information, I use two CR2032 coin cells to power the timer. I use mine twice a day, every day and polish my gold and silver mine of fillings until they shine like the sun.