Post for September 6, 2014

YIPPEE! I received my three PCBs from OshPark yesterday…oh and of course there are the packets of chips that I bought from digikey and the stencil from OshStencil…exciting…

Healthy pH PCB

Now that I have come back from my yoga class, I’m ready to get started assembling the Healthy pH Shield.

Part Placement

After building the PCB in the Contextual Electronics Session 1B, I’m going to start with a process that I learned as I went along….as I go one step beyond clueless…I find when attempting to solder components on a PCB that getting a bit more organized goes a long way in lowering frustration and gives me the best chance of being successful.

The first thing happens during BoM building.  Build the BoM such that one of the columns is the Component number shown on the board layout.  

For example, here is the board layout of the Healthy pH Shield pointing out where the two diodes are:

Healthy pH Board Layout With Diodes Highlighted

Here are columns included in the BoM:

Cmp # MFG MFG Part Number
U1 Microchip Technology MCP6241T-E/OT
P1 On Shore Technology Inc OSTTE080104
U2 Microchip Technology MCP3901A0-I/SS
X1 TXC 9B-4.000MAAJ-B
C1 Kemet T491A106K006AT7280
L5 Taiyo Yuden BK2125HS101-T
R5 Vishay BC Components NTCLE100E3109JB0
U3 Fairchild Semiconductor MC78L05ACHX
D1,D2 Comchip Technology CGRA4004-G

The label on the digikey bag containing the diodes has the manufacturer’s part ID:

Digikey Label

Oh – and when ordering common parts like resistors and capacitors – it’s best to order in larger quantities – say 50.  A discount kicks in and these parts get used up.

Other organization aids revolve around the chips.  As I open the chips, I’m going to:

  • store as many as possible in an SMT storage case (this is the one I got) .  I’ll label the itty bitty storage cases I use using my handy-dandy label maker (here’s the one I got).  Both of these awesome recommendations came from another student in the course.

  • place chips on one of the other Healthy pH Shield PCBs – I’ll refer to this as the placement PCB – so that after I apply the solder, I’ll know where to place the chips on the board I will solder.
  • stay calm and drink coffee…
oh…and adding one more thing – I’m not opening the Digikey box-o-chips until I am ready to put the chips away or use immediately.  I lost a couple of chips…vacuum cleaner?  dogs? cats?…darn it.

Start Placing Chips

Equipped with the board layout in the PCBnew editor, I start placing the chips…and the first one I place is the Power Jack Connector.  This brings me to….


hmmm… the through holes, well – they aren’t through holes on the PCB and they certainly don’t match the through holes on the barrel jack. Yah well…I screwed up.  Luckily, my staying calm strategy is helping me through this boo boo.


Moving on…

I start placing the diodes, capacitors and resistors on the placement PCB.  I’m not checking to see which direction a diode should be in since this is just about placement and not current flow.  Like a box of puzzle pieces missing a few pieces, I cannot find U1 (MCP6241), C1 ( 10µF tantalum capacitor), and R3 (10K resistor).  I guess I’ll be putting in another order to digikey.

Parts on Healthy Shield

Next Steps

I’m going to try out the stencil and solder on the SMT parts I have.  I’ll order the missing parts from digikey.


Thanks for reading this far.  Please find many things to smile about.