How To Effectively Check A PCB Schematic

[stextbox id=’info’]The following is a sponsored post, brought to you by Altium and Mil-Max.[/stextbox]

When you design a printed circuit board, you often begin with creating a schematic that will be used as a reference later in the process. Of course, schematics for PCBs can be very long and complicated which can make checking them for errors quite difficult.

Here, we are going to tell you how you can effectively check your PCB schematic. Keep reading to find out more about this.

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I’m a notorious task-starter, and not a great task-finisher.  My garage is littered with old projects that are collecting more dust than accolades.  I can lean on the old, dependable excuses 1 but really that’s lame.  If every moment is the new normal, then there aren’t any excuses.  Our hobbies define us, and I love my hobbies.  So it’s time to get serious about some side projects.

One thing that I’ve always responded to positively when it comes to my side projects is a good deadline.  Nothing motivates like external pressure.

The deadline this time?  Something called the Galactic Side Project Month  (GaSiProMo) challenge.  You’ve heard of Hackathons or Codefests?  This is similar, but with a more sane schedule of an entire month for completion.

It was tempting to submit one of my more languishing, challenging old projects.  But in the end I decided on something new and fresh, one that is slightly more achievable.

Osram 5x7 display module
Osram 5×7 display module

For GaSiProMo, I’m going to get this display up and running.  It’s an intelligent LED matrix.  I might even throw in a keypad to change the patterns and such.

I’ve had this display module lying in my Big Bin of Parts for… more than 10 years.  At this point:

  1. I’m not convinced it even works.
  2. I don’t know what color the LEDs are (the module comes in yellow, red, and green).
  3. And I’m certainly not convince it will be that cool, but at least it’s a project that I’ve always wanted to do.

So there we go.  I’ll post regular updates here and over at the GaSiProMo website.  It’s time to blow the dust off some of these old projects.

IKEA kitchen light mod, part 2

A while ago, I modified my daughter’s little kid kitchen.  In that project, I found my design self teetering on that edge between two goals: get-it-done on the one side, do-it-right on the other.  I had chosen the former and even my 2 year old (at the time) could see that this was a critical design mistake.

As a quick refresher, I had thought Those Thoughts 1.  “Wouldn’t it be cool if her cute little IKEA oven had a light that turned on when the cute little door was opened?”  Well, yes, but perhaps it would have also been cool if I’d considered the very likely fault condition wherein my toddler would leave the door open.  Toddlers do that.

And you guessed what happens next: batteries died.

A very wise engineer once told me, “Rob, there’s never enough time to do it right the first time.  But there’s plenty of time to fix it later.”

Well, here I am, fixing it finally.

I knew that a timer was in order.  So I blew the dust of my Forrest M. Mims III Radio Shack booklets, particularly the indispensible 555 timer book.

MIMS 555
The 555 according to Forrest M. Mims.

When I was done, this is what I cooked up:

output FET circuit
This is the output driver circuit.

truth table
This is my truth table for operation and the switch input circuit.

So to explain the “truth table“, the operation works like this:

  1. user (in this case, the kiddo) opens the oven door
  2. added lights inside oven turn on and remain on for about 10 seconds
  3. if user does not close door within this time, the lights go off to conserve battery life
  4. closing the door within the time frame resets the timer and turns the lights off

One other critical circuit requirement that the above Mims diagram does not account for was with the trigger input.  His classical circuit only triggers on level changes, active low.  In other words, for as long as the input is held low, the timer would be in standby.

That wouldn’t work for me, since I wanted the timer to start when the door opened.  That’s an edge-sensitive requirement.  I found a nice, easy capacitive switch solution:

Screen Shot 2013-08-02 at 9.39.57 PM
edge-sensitive input circuit

The results, finally, were as they should have been: nice well-lit oven that doesn’t wear out the toy batteries. My engineer buddy would agree.

updated timer circuit
Lower left corner is the added timer circuit.

lights on!

Cell phone connector fix

My good friend James contacted me with an electronics problem.  Seems his daughter’s cell phone was on the fritz.  So I agreed to take a look.

She has a Pantech P7000 flip phone, but it stopped charging.  I asked a few questions first to understand the nature of the problem.  For instance:

  • Has she tried other wall chargers? Yes, all give same symptoms.
  • Has she tried other batteries? Unknown.
  • Has she tried wiggling the cable to see if it makes connection? Yes, and it does.

James gave me some great info, so I knew what I was in for.  My guess was that the charging connector on the phone was going bad.  I’ve seen it before.  James sent it to me to have a look:

The first thing I did was have a look at the charger, just to test out the verbal info I gathered from James.  With a set of helping hands, I probed out the power and ground pins:

charger cable connector

I saw a nice steady +5V, so the charger was good.  Although its plastic shell was a bit wobbly, it seemed to be functional still.  Now, onto tearing apart the phone.

I couldn’t find a tear-down guide online, so I had to figure it out for myself.  There’s one obvious screw above the battery compartment:

reverse without battery

But I had a hard time finding the other hidden screws.  Turns out, there are four hiding underneath a bezel surrounding the keyboard:


Once those are gone, the assembly comes apart rather easily:

Now the back shell can be removed.  When I did, the charging connector tumbled right out.  So it was no longer even attached to the PCB:

connector gone

Here is a closeup of the connector:

bottom side

You can even make out the copper pads still attached to the pins, which have ripped off of the PCB.  That’s never a good thing!  This type of damage is actually quite common in consumer electronics.  This interface isn’t always well designed on most cheaply produced gizmos.  And yet, it’s an area that is very high-traffic; in other words, the mating cycles of the charger or serial cable to the phone is always quite high.  As a designer, I would prefer these interfaces to be more robust.  But then, I’m more interested in lifespan of my electronics, whereas most electronics companies would prefer you buy new products every 6 months.  I digress.

At this point, I wasn’t yet sure I could repair this.  There was significant damage to the PCB pads (some pads entirely gone!), so I first cleaned off the remaining pads by re-tinning 1:

damaged pads

Next, I cleaned off the pins of the connector.  Then I re-placed the connector down on the board and soldered it back on.  I got maybe 80% coverage of pins to pads.  The number of pins on this connector is maybe 10-12; obviously only 2-4 of which are used for the power charger.  So all that was strictly necessary were those sets of pins.  As luck would have it, those power pins were still intact.  The phone is back to life!


Full Project Gallery:

iPod jukebox (phase 2): prototype

You remember the first phase of the iPod jukebox, yes? To jog your memory, the basic goal was simple. How do I make these dust-collecting components:

…work with my iPhone in order to have music in my workshop?  Simple concept, not so simple electronics. The project is mostly a connectivity issue, i.e., there are tons of inputs and outputs that must all be managed with connectors and wiring and power regulation.

On paper, the system looks something like this:

system schematic

In Phase 1, I had done a substantial amount of wasted work with one such cable: the audio/power cable for a first & second gen iPod.  Since the project had been shelved so long, several generations of iPods and now iPhones have come and gone.  Well, in that time, Apple has settled on USB as their power bus of choice, rather than FireWire.  Thus, I had to likewise change directions on this project to accommodate my iPhone (rather than the antiquated iPods).  Mounting options naturally have to change as well.  And the overall enclosure gets modified too.  It’s quite a ripple effect when your central component (the music player!) gets the switch-aroo.

I was locked in a brain-freeze for quite a while on this part, the mounting and enclosure.  I had been stuck on the idea of trying to make a “pretty” Apple-esque Plexi box.  But I finally admitted to myself that this is just above my skill set.  I have a hard enough time making ugly black plastic kit boxes look pretty, let alone clear Plexi where blemishes show so easily.

So instead, I’ve decided to embrace ugly.  Why not just make this phase of the project an intermediate step rather than the final step?  My garage is already an acceptable and appropriately dirty place, as is the attached workshop.  Just let this jukebox fit in with that kind of environment.

So I completely re-thought the enclosure phase.  I began cobbling together other old cases, car mounts, and such to make a quick enclosure that would be practical, yet secure.  Such parts included:


iPhone gooseneck holder iPhone holder #2


USB audio iPhone cable


USB Car Charger for iPod charging circuit

In putting all these items together, it now (unintentionally, I assure you) might resemble something else entirely, as you’ll see in the project gallery below 1.  But hey, this jukebox does reside in the man-cave after all.

What’s in store for Phase 3?  Coming soon, I’ll package all this mess a little nicer.  I have some connections in the machine shop world.  I also will reveal this gizmo’s name, so stay tuned.

Project Gallery:



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