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Assembling a 3 display board

Here's a brief run down of what it takes to put a board together


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The first thing you need to do is finish the board properly since the board comes just roughly cut out.  Here I'm using a 1" belt sander to sand into the outline trace of the board.

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If your real finicky you can file the last few thousandths into the trace.  

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Here you can see, sort of, that I've filed about half way into the trace and the trace is visible on the forward leading edge. 

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I'm now ready to remove the outline trace.

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The trace will pull off quite easily to remove it.

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The tools required to do the rest of the job.

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Let's do the delicate part first...

I've used the needle nose pliers to protect the glass shell of the magnetic reed switch as I make the first 90 degree bend.

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The reed switch is then placed in the board and the needle nose pliers are used to hold and mark where the second 90 degree bend is made.

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Here I've fully installed and soldered in the reed switch for the power.

Remember to check to make sure you bend them the right way. Without a magnet present the power switch should have continuity between the two pins that have the traces running to them, and no continuity for the back light reed switch. 

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Flip it over and trim off the extra part of the leads with right angle cutters.

Do the same for the back light reed switch if you choose to use one.

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On the protective plastic sheeting cover mark the displays with numbers which you'll remove when your done.

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Turn all the pots fully clockwise.

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Hook up + 9 Volts to pin 1 and ground to pin 3.  Attach a DVM across pins 8(+) and 10(-).  Pin 1 is denoted by the black triangle on the white label and the pins are numbered consecutively around the display counter clockwise, while looking at the back.  So, in this picture pin 1 is in the upper right, pin 6 lower right, pin 7 lower left, and pin 12 upper left.

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Read the millivolts across pins 8 and 10 and record the value.

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Now do the same for the other two displays.  After you've got all the values, go back and using the trim pot on the back adjust the value across pins 8 and 10 to read the lowest value you recorded.

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Mix up some two part epoxy

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Cover up the trim pot to seal and lock it making sure the blob isn't to high that the display wont sit properly when installed on the board.

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Ready to roll.

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Put the battery clips on the battery and install it on the board, double check the polarity.  I find it useful to use a rubber band to hold it in place.

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Solder the battery clips in.  The polarity is correct .... right?

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Install the displays, lining up pin 1 on the display with .......

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..............Pin 1 on the board.  Pin 1 on the board is the square through hole and is also marked with a 1. 

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After you solder the displays in, trim the excess leads with right angle cutters, you can do the excess battery clip lead material while your at it.

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Next install the sensor trim pots.

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Install the header connector, backlight jumper or resistor, and the sensor load resistors if needed.  Again trim all the excess lead material from the back.

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D-Flux the back of the board to remove all the solder flux, double check all your connections and solder joints


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So now we're ready to install the battery, test the power and back light switch, make sure there's no stray voltage between the sensor ground and the sensor positive connections on the header connector and then hook up some sensors.

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I didn't include this in the above description but I have started to use conformal coating on the boards I've put together.  It could aid the board and sensors if you should flood your housing.

Special Note 02/2005:  All boards now come with Solder mask, which is the green coating you see on standard industry PCB's.  So if you want to use conformal coating it only has to go over the the solder connections, not over the whole trace runs.

As of late I haven't been using it and assume I wont flood.

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Use it as you put the board together making sure that everything that runs a signal is coated when your done with the construction.  I usually start construction by coating the parts of the board I wont be able to reach after something is installed, with out getting it into the through holes.  The displays are the trickiest part.

Well there ya have it.

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