Friday, 26 July 2013

Design and Test

Testing, Day One.

It's been a while (a large part was waiting on parts - I'm looking at you Futurelec!) since I posted about my Alarm Monitoring system but as I've finally been able to get some build and test underway I thought I'd share the progress.  Which is a nice way of saying I'm not finished yet.

Step By Step

With this design I've incorporated a fair few new circuit blocks I haven't tried before, being:

  1. FET Current Limiter Circuit
  2. 4V, 3A (TWELVE WATTS BABY!) Switch Mode power supply
  3. AVR microcontroller (yes, never used 'em before)
So to start, I loaded only the power supply section before placing other parts.  This is a good practice when prototyping as if you stuffed something up, you don't blow up the rest of your board.  I've actually designed in zero ohm links on the power supply rails which could also prevent the same destruction but through experience I prefer to do it his way.

Zero ohm links are good for when you are setting up production boards.  You can adjust anything that needs adjusting in isolation before installing the links.

But for prototypes - Why load everything on your first prototype when a SNAFU in any area could make the whole exercise pointless?

Partially Loaded

Thursday, 25 July 2013

Polyswitch Current Limiting

Polyswitch Testing

Just a quick little video I took while testing my Raspberry-Pi protection circuits.

To recap, I was testing the current drawn when a 5V1 zener clamp is protecting an input from an over volt condition.

Monday, 22 July 2013

iPhone 4 Screen Teardown

Reduce. Reuse. Recycle!

In an effort to get fit, I'd been going for long walks.  Anyway, I enjoy listening to podcasts while doing so, and I did this on my trusty iPhone 4.

Or should I say 'rusty'  The sweat in my pocket payed havoc with the end connector and when some obvious (non-photographed) corrosion set in I couldn't charge my phone.  Eeep.

So out with the contact cleaner and toothbrush and I could soon charge my phone again, but the contact cleaner seeped up into the phone and left cloudy dark spots on my screen, just like this. Again I'd taken no photos of my own at this stage.

But at the end I got some sweet LEDs to play with!

Power Supply Protection for Raspberry-Pi

Defining the Problem, Again

The power rails of the Raspberry-Pi are bought out on the GPIO header as well as the IO pins.  This is both a blessing and a curse.

The advantage of this is that you have 5V and 3V3 rails available to power your circuitry that you are hooking up to your GPIO pins, but again, as the Raspberry-Pi doesn't have any protection circuitry you run the risk of killing your Raspberry-Pi through:

  • Short Circuiting the Rail
  • Reverse Biasing the Rail
  • Over-Volting the Rail

Friday, 19 July 2013

GPIO Protection For Raspberry-Pi

Or How Not to Let the magic Smoke Out

Previously I've written about my love / hate relationship with Polyswitches, and discussed some input and output pin protection methods.  I was looking into this so I could make a breakout board / protection device for experimenting with my Raspberry-Pi and not let out the magic smoke.

I could say it's to help kids / beginners protect themselves from basic mistakes, but even after practicing Engineering for nearly 20 years I have learn that Murphy still bites, so it's also a lesson in self preservation :)


Friday, 12 July 2013

I've Seen The Light

Unintended Consequences

Around 4 years ago, we built our house.  The builder delightfully quoted an extra $1500.00 to convert our standard garage roller doors to remote controlled units.  While recovering form the shock of that addition I was strolling though our local Bunnings when I came across these DIY kits.  

If I recall correctly, they were even cheaper back then, and I managed to get a pair for under $500.00

So a little DIY later, I was up $1000.00.  Win.

Installed Roller Door Remote Controlled Motors.

Cashed up, with remote controlled roller doors.  Life was good.  But something was missing....

Yep - no lights were fitted to the roller door motors.  So when I parked in the garage at night, and closed the door, it was a bit hard to see.