Category Archives: Electronics

Cable Improvising

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A couple of weeks ago I was at Edinburgh Hacklab and wanted to test a USB to Serial converter. I plugged the USB side of the converter into into my netbook and then went about trying to find a suitable Null Modem cable to make a connection to a RS-232 port of the hacklab PC.

I knew the correct cable for the job but the one I own was sitting at my parents house. So I went rummaging in the “adapters of all kinds” box and built myself this work of beauty.

Null Modem "adapter"

Null Modem “adapter”

It consisted (excluding USB to RS232 convertor) of

  • 9 pin Female-Female Gender Changer
  • Male 9 pin to Female 25 pin straight through convertor
  • 25 Pin Male-Male Gender Changer
  • A great big heavy “Null Modem” converter that has been lying around the lab that has two female 25 Pin connectors
  • 25 pin Male to 9pin Female straight through cable.

Amazingly this worked and I was able to type in a terminal on my netbook and see the output at the other end.

Remote Control Central Heating

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Why?

Over the summer I moved into my own flat. As the weather starts to get colder I’ve found myself thinking that the heating might need switched on once in a while. I don’t need to heat my flat if I’m not around, as long as it’s not so cold the pipes freeze! I’m generally out doing something most weekday evenings and I’m not sure in advance when I’ll be back. I would like to control the heating remotely so i can switch it on when I’m 20 minutes from my flat, just like they showed on Tommorows World in the 1970s. Continue reading →

My First PCB

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Recently I’ve started a project to add some RGB LEDs around the rim of a Sombrero. Naturally having each LED individually addressable and dimable (using PWM) was a given. Although off the shelf LED strips may have fitted the bill, either as is with a bit of modification I thought this would be a good opportunity to try making some BlinkM clones. I found the Ghetto Pixels – Building an open source BlinkM instructable and decided to use a small PCB to keep thing a bit neater.

After following this very useful guide I was able to get EAGLE 6 running on Debian squeeze and was ready to design the

After many hours spent getting the components and tracks laid out as neat and optimised as I could I showed my design to a few experienced PCB hackers at Edinburgh Hacklab. A useful bit of advise was “Don’t torture the board house”, for example just because they claim to do 6milli tracks doesn’t mean you should use such thin tracks if 10milli tracks are suitable. I also printed the board layout onto normal paper to check that the components fitted and nothing looked obviously wrong.

Printed on normal 80gsm paper at real size (~25x25mm)

I’ve opted for a mixture of surface mount and through hole components. The LED current limiting resistors and decoupling capacitor are surface mounted. I’ve chosen the relatively large 1206 package for resistors, with the rational that it should be easier to solder. Using a thru-hole DIP version of the ATTiny consumes extra board space but given my limited surface mount experience it’s probably wise to learn to walk before running.

My Board

The boards are being manufactured using SeeedStudio’s Fusion PCB service. As the smallest board they do is 50x50mm and my board was 25x25mm I’ve panelised 4 of them onto each by following the Panelizing PCBs Seeed Using Eagle instuctable. I placed my order and submitted my design file on 30th October, received an email on 1st November saying the order was “In production” and was “shipped” on the 6th November. From the experience of others I would expect the board to arrive 2 to 4 weeks after ordering.

Fingers crossed I haven’t made any design errors….