From schematic to board
If you have a known working schematic, you can get a printed circuit board produced for about $70. However, I'm not going to get into what you need to do to design a board, and 70 bucks is 70 bucks. I'm going to build all of these projects on proto boards:
Proto boards (prototyping boards) are a piece of phenolic or fiberglass board with a grid of holes and solder pads.
- The boards are usually 1/16" thick, but this varies.
- The holes are usually on 0.1 inch centers to fit standard IC pin patterns, but other layouts do turn up. Always check this spec.
- Various pad patterns are available, from none to complex ones with power busses and edge connectors. I find two patterns most useful-- the one pad per hole shown above (pads on one side only) and patterns that exactly match a solderless breadboard, like GC Electronics 22-508.
- Pads may be square or round. The round ones build a little neater (less chance of solder bridges) but the square one can be persuaded to accept smd parts. (See plastic diner.)
- They come in all sizes-- I generally keep a bunch of 2" x 3" or similar sizes around and order bigger ones as the need arises. Some are sized to fit specific cases-- handy when building a slick product.
- Good ones have tinned pads-- cheap ones (I'm looking at you, Radio Shack) are varnished plain copper and need to be lightly sanded before use.
The boards can be cut to size by scoring along a line of holes with a glass cutter or razor saw and snapping along the score. This is easy if you clamp it into a vise.
The hardest part of transferring a project from the schematic to proto board is knowing where to start. No, really-- you have to consider the position of any controls on the board, any indicator lights, and how wires that lead off the board will be dressed-- you usually want all wires to come off of the same edge so you can easily turn the board over for service. In this case, there are two LEDs (I'm building two circuits on the same board) that will have to fit holes in the panel. Here are the parts concerned:
- A panel
- a hunk of proto board
- 2 2.2k resistors (Actually I changed my mind after taking this picture and used 2k resistors.)
- 2 LEDs
Note that I have already drilled holes in the panel. The small holes match the mounting holes in the proto board, and the large ones are a bit larger than the LEDs. I used the proto board to mark the panel for drilling- I lined it up straight and pushed a #61 drill on a pin vise through the holes to make a mark. To get the panel, board and LEDs lined up, I dry assembled them:
Everything is mounted on two 4-40 screws. The proto board needs to be held clear of the panel about 1/4" or so. I use nylon spacers for this, but anything will do, scrap styrene, wood, drinking straws, some folks use extra nuts. The nuts on the top are nylon-- steel works, but will short out a few pads, and Murphy is always watching to see that those particular pads become necessary.
With the work assembled this way and the LEDs pushed firmly through the panel, I soldered the LED leads.
Soldering these is not as difficult as soldering track. For one thing it is quick, and you are not trying to reach behind a delicate water tower.
- If you have never soldered to circuit boards before, practice with odd parts on scrap board.
- Make sure the pad and lead are clean-- they will be if they are new, but it never hurts to give the pad a touch of sandpaper before starting a project.
- Use fairly thin rosin core solder. (No Acid flux here!)
- Use a medium point tip at 650-700° F.
- Apply the iron tip to both the pad and lead and start counting at 60 BPM.
- On the count of 5 touch the solder to the lead and pad-- it should flow.
- On 7 lift the solder.
- On 8 lift the iron.
- Watch for the sudden color change when the solder freezes.
Things that can go wrong
- A huge blob means too much solder-- don't hold it down so long.
- If the pad is barely covered that's not enough solder. The solder should fill the pad and make a cone up the lead-- the rightmost joint above is the best.
- If the solder is rounded at the pad or lead instead of a cone, one or the other was not hot enough. Be sure the iron touches both lead and pad, and wait a bit longer before applying solder. (Many folks put a preliminary drop of solder on the tip of the iron to help the heat transfer. This is fine, but it can be overdone.)
- If the solder is an ugly grainy grey, the lead moved as the solder was freezing- you have to do it again.
- A bit of brown shiny rosin around the joint is natural. A lot of black crispy rosin means your iron is too hot.
There are more parts to add, so at this point the panel was removed.
Next I added the resistors. Note the colored stripes. These reveal the value of the resistor. They read from left to right (in this picture anyway- the gold or silver stripe comes after the value)
- First digit- in this case 2
- Second digit-- 0
- Number of zeros to follow (or multiply by ten to this power) again 2
So the value is 2000. AKA 2k ohms.
The color code is published many places- it is basically the colors of the spectrum:
- 0 black
- 1 brown
- 2 red
- 3 orange
- 4 yellow
- 5 green
- 6 blue
- 7 violet
- 8 grey
- 9 white
Well, sort of a spectrum. Like I said, it's easy to look up. Download a chart, color print it and hang it on your shop wall. These colors are used to mark a lot of things. The gold or silver stripe is tolerance- gold is 5%, silver is 10%, no fourth stripe is 20%. What, did you think electronics was a precision science? 1% tolerance is available, but expensive. Instead, we design so 5% is close enough.
Note that I placed one lead of each resistor close to a lead of the LED. I then turned the board over and bent the resistor lead around the LED lead:
Then I soldered the leads together and clipped off the excess.
Next was to bend the remaining leads in a curve over a nearby pad. Wires will be soldered to these that will connect to the track:
The wire is pushed through the pad and bent over the associated lead. In this case I used 26ga solid wire, but if the wire runs very far I recommend stranded. Tin stranded wire before soldering it, and enlarge the hole with a #58 or #61 drill if necessary.
It's a trick to visualize both sides of the board at the same time, so here's a close up of one of the circuits with the symbols drawn in:
This is a situation where dyslexia is helpful! That extra resistor lead ws soon clipped.
Putting it back together:
I envisioned attaching the wires to some sort of connector to complete the run to the track, but which kind will depend on your preference. A barrier strip attached to the panel would be a good choice.
And the user view:
More holes are needed to mount the panel to a fascia, but again that should match what is already in use.
Next: a bit more complexity, but not much.
pqe