CircuitGizmos

Electronic Products for Creative Minds

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Prototype PCB Design/Documentation

I use a lot of the protoboards like the one sold here at CircuitGizmos for developing prototypes of all sorts of circuits.

pcbtop

Too often, though, the circuits are created but the effort isn’t documented. Often times the prototype is considered for reuse or modification later, but then it has to be reverse-engineered. With document templates that have a diagram of the circuit card on them I can print out a page and mark up that page as I build the prototype.

The template pages have the front and back of several PCB boards that are a grid of holes with “donut” copper on them. Here is the front image from the board sold here at CircuitGizmos:

2009-07-07_205359

And the back side:

2009-07-07_205416

The template files cover seven of the boards that I use for creating prototypes. I print the .PDF file, three-hole-punch the page, and clip it into a binder where I collect my prototype documents. I can mark up the page to show where I’ve placed components and connectors. There is room on the page for notes. The bottom of the template pages contain a title block for documenting the project.

Here are the .PDF pages:
board1template.pdf
board2template.pdf
board3template.pdf
board4template.pdf
board5template.pdf
board6template.pdf
board7template.pdf

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Up, up, and out of the way.

My keyboard stopped working.

Not the whole keyboard, mind you. Just some specific keys. I had taken the keyboard apart and cleaned the inside several times to get it to work again. It would work for a few weeks, but then stop working again. Apparently it wanted to retire.

It was a wireless keyboard that I had for a while. I REALLY liked the fact that it was wireless, because I often set the keyboard and mouse (also wireless) on a shelf when I want to use my entire desk surface. I like to have a lot of desk surface when I need to spread out schematics and other multi-page documents. This time, though, I decided that the thin replacement keyboard and lightweight mouse could be modified to “stick” on the wall at the back of my desk for when I wanted to put them away.

magnet0

I decided to use some strong magnets to keep them on that wall. The keyboard and mouse weight would rest, as you can see from the picture, on the “splash guard” on the back of my desk. (My desk is made from a counter top.) The magnets wouldn’t need to bear the weight of the keyboard and mouse, but only needed to keep it upright against the wall. In the picture below you can see the battery cover for the keyboard.

magnet1

I stuck a strong magnet in the area of the keyboard batteries just as a test. One magnet was a little weak to do the job, so I planned on two. In the picture below you can see that there is some space next to the batteries, but still behind the thin plastic of the cover. My plan was to drill a hole in the plastic there and insert the disk magnet.

magnet2

I also chose a spot in the inside of the keyboard to place a second magnet. I disassembled the keyboard and used a clear two-part epoxy to secure the larger disk magnet.
magnet3

The mouse was a candidate for the same treatment. Opening my mouse I discovered that there was just enough space for another small magnet on the bottom of the case front-and-center just ahead of the mouse wheel.
magnet4

The two-part epoxy that was supposed to take 20 minutes to cure was taking a long, long time. It was some clear epoxy I had purchased years ago to repair clear plastic, so I’m sure the trouble was that it was well beyond its use date. Below the magnet beneath the battery cover is stuck in place by some epoxy that is only tacky at this point.

magnet5

The wall behind my desk is wood covered with a thin layer of white PVC. It is NOT magnetic. So in the places where I need to have a magnetic material – immediately below the strong magnets – I used this hardware:

magnet6

The photo below shows the simple holes that I drilled in the wood. I have access to the area behind this wood. That makes it easy to install the screws/nuts. Two holes are shown here that the magnets in the keyboard will attract once installed with metal.

magnet7

The epoxy is STILL not cured at this point. So I decided to do something about the little wireless receiver for the new mouse and keyboard.

magnet8

I didn’t care for the way it was made. It was meant to sit up in your desk, elevated by an arch of plastic. I decided that the plastic was in need of being recycled. 🙂

magnet9

In the pic below you can see the simple innards of the receiver. I took it apart to work on it.

magnet10

Here I scored a line on the plastic where I will cut off the extraneous part.

magnet11

I used a nibbling tool to remove the plastic that I didn’t want. After nibbling, I used a file to smooth the rough-cut edge.

magnet12

Reassembled, the receiver box looks like this:

magnet13

On the back of the plastic receiver box I used a square of exterior double-stick foam adhesive tape. I will stick the receiver to the wall tucked up behind the LCD displays that are also mounted on the wall.

magnet14

Below you can see the receiver box hanging down against the wall before being mounted in its place behind the LCD monitors. You can also see, in the picture below, the three places where the magnets will be attached.

Now where was I? Oh yeah, I was waiting for glue to dry.

magnet15

The epoxy finally cured, and the keyboard and mouse stick to the wall. At night when I clear off my desk (Yes every night my desk is cleared. I love coming in to my desk in the morning without the debris of the day before strewn all over.) or when I need to use all of my desk without the mouse and keyboard in the way, I “stick” my mouse and keyboard against the wall. (You can see the old keyboard to the right in the pic. So long, old friend.)
magnet16

Just in case you are wondering, the middle two monitors are Windows, the right is Ubuntu, the left OSX. I use Synergy to move between the machines with a single keyboard and mouse. Otherwise I’d have three keyboards and three mice stuck to my wall…

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Antistatic Desk Strip

I work at my desk on prototype electronic devices. To the left of my keyboard is an antistatic mat that usually contains embedded prototypes and other electronic devices. The antistatic mat protects those devices from static discharge when I touch the mat before handling the device. Sometimes, though, I will handle the device right at my desk while I’m doing embedded design work.

I don’t like to be tethered by an antistatic wrist strap. I would much rather put a big old mat over the surface of my desk. The trouble is – antistatic mats make poor desk surfaces.

So I decided that the best solution would be a static discharge strip right on the front edge of my desk surface. I couldn’t find anyone that made such a beast, so I made my own. And I did it for about two dollars.

11strip

Below is a picture of the front edge of my desk without a strip:

1strip

My desk surface is made from a six foot long counter top from a home center. It has a smooth writing surface.

The strip is made from a disposable wrist strap from Digikey that is about $1.50:

2strip

The antistatic wrist strap is meant to be used once and tossed. It has static conductive material running the length of the strip that is wrapped around your wrist and then the other end is attached to a grounded metallic surface.

If you unwrap the strap, the leading edge has the conductive strip of material that should be put in contact with your wrist skin. On either side of the conductive strip is adhesive material much like athletic tape. The strip continues “bare” for a little it – long enough to wrap around your wrist. Then the conductive strip is covered by the adhesive material forming the “cord” just like the cord of a regular wrist strap. At the far end of the strap is a bare and sticky sheet of copper to adhere to a grounded surface.

3strip

To use the strip, I want to get rid of the adhesive tape material. The strip pulls away easily:

4strip

But when you get partway down the length of this disposable wrist strap, the conductive material is cut in a zig-zag pattern. No doubt this is to make the strip longer electrically to increase resistance:

5strip

There is just no way to make use of this section of the strip. It just stretches out like the photo below:

6strip

Luckily this section is only near the wrist end of the disposable wrist strap. I just cut the strip off at this point and I only lose a bit over a foot of conductive material.

The adhesive tape is removed all the way to the end where the sticky copper connects to the conductive strip:

7strip

Once the adhesive tape is removed from the strip, there is nothing sticky about the strip. So on the edge of my desk I ran a length of double-sided cellophane tape. The double-sided tape is a little wider than the conductive strip:
8strip

The copper end of the strip is wrapped around the bare end of a wire that leads from the side of my desk to a ground point:

9strip

The strip is then run from one end of my desk about 30 inches to the middle. This puts the strip directly in front of me while I work. Since the double-sided tape is slightly wider than the conductive strip, I used an Exacto blade to cut off the excess tape:

10strip

The strip sets in front of my keyboard – a place that I touch frequently with my arms:

11strip1

This has saved my bacon more than once. I know that shifting around in my chair I can conjure up a significant static charge. With the strip there I am constantly at ground potential.

Many years ago my mom “grounded me for life”. I’m just fulfilling that command. 😛

Please post any questions you may have.

Update:

LifeHacker (http://www.lifehacker.com) just pointed to this article. I appreciate the attention – I read Lifehacker every day. I want to clear up their text, though. “He had an antistatic mat, but it was on the small side, and expanding it to the size of his work surface was out of the question due to cost and space needs.” I’m not sure how that conclusion was drawn. I have mats to the side of my desk and I didn’t want the mat surface for my desk. Antistatic mats are a poor writing surface. And, Ladies, there is nothing small about my mat size. Wink. *cough* *snort*

On a serious note is the concern about resistance to ground. If you work on live circuits, you do NOT want to be well grounded. I wrote “The copper end of the strip is wrapped around the bare end of a wire that leads from the side of my desk to a ground point.” and in my setup my ground point is my static mat connection. If you implement this desk strip, you should consider adding a series 1 mega ohm resistor in the line (the wire) if you connect directly to an earth ground connection. Play it save – do NOT ground yourself when working with any circuit that is live.

Stay safe!