Friday, 9 December 2011

Updates on the Project

My sincerest apologies to those that follow my blog....

I haven't had the time to do any posts or updates in some time.  I have been thinking about the project and I have done some work on it.....

I am in the process of making up what I call the seven segment display modules which will be the 4x Seven Segment LEDS and the associated shift registers.  I was intending to etch and make a PCB but as I currently don't have access to etching facilities I haven't gone down this route.  I bought some matrix board off an excellent small electronic components distributor via their online shop:

They don't have as large a selection of components as RS or Farnell but they have most of what I need and they don't mind small orders.  Their service is excellent!  I order before 12am on a weekday and more often than not my stuff is delivered the next day....that kind of service seems hard to find for electronic components in the UK and this is at very reasonable prices.  I wholeheartedly recommend them.

Here is the matrix PCB:

What I will have to do is solder in the components and then either use wire links to make the connections or make solder tracks.  There are pitfalls in using matrix board and this will become apparent as I post more photographs of the construction.

A few tips when using matrix PCB:

  1. Plan your layout carefully.  Place the components on the PCB in a rough semblance of where you want them to go.
  2. Ensure you have display components centred and placed in a logical fashion.  Try and ensure you have enough room to wire the components together.  It can be difficult to go back once you have started.
  3. Once you are certain of where you want to place components begin soldering.  I recomment soldering the corner pins first off.  Then once you are comfortable with the component placement solder the rest of the pins.  There is no rush when doing this....I would also avoid hangovers and coffee!
  4. Use a sensible heat setting on your soldering iron.  Soldering at too high a temperature can and DOES melt the glue that holds the pads onto the FR4 material.  Wire up the circuit slowly testing each section as you go.  Desoldering and moving components can be difficult.  I write with experience in things not going according to plan!

For those that don't know most electronic circuits use a special material as the base surface called FR4.  It is glass reinforced plastic which is an excellent insulator.  Copper material is glued to the FR4 to allow conductance of electricity.  The copper is then removed to create tracks or in my case a matrix. 

As I write I am half way through completing the construction and test of the first display board.  I hope it all comes together.  Check out the mess of wires on the underside!!

I made a classic mistake in not considering how thick wire can cause issues when making connections and this will cost me dearly.  I also didn't use a sensible wiring practice when making the connections and will have to work out which wires connect which resistors to the LED segments.  I should have wired the shift registers first.  Hindsight is a wonderful thing!  I can still get this working but I think I will construct the other PCB with the same component placement but wire the shift registers first off.  

Well that is about it for now.  After I have both display boards constructed and testing and working I will be showing how we can use Rotary Encoders to set the count down time.  I'm still hopeful to get this finished for Christmas!!  

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