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P13036 – Notification Alert System
PCB and Soldering Notes
Elizabeth Phillips
Table of Contents
I – PCB Continuity Testing
II – Component Soldering
III – Functionality Testing
IV – Debugging
V – Results
I. PCB Continuity Testing
After receiving the PCB from the manufacturing company, continuity testing of
the board against the designed PCB layout and the Battery Charging/Power Regulation
Schematic was carried out. It was discovered that many of the components were not
properly grounded due to accidental “islands” created on the PCB. The entire front and
back layers of the PCB were designed to be a ground plane. However, these “islands”
that were created made certain components to be cut off from the ground plane of the
entire circuit. This was caused by placing components into a part of the PCB where the
ground is encapsulated by traces or other components, thus acting like a floating ground.
In order to fix these issues, small holes were drilled, where applicable, from the
front ground plane to the back. These holes were then filled with solder to ground the
“islands” back to the main ground of the circuit. If a hole could not be drilled, wires were
used to connect the component to a known working ground. Once all the ground
“islands” were fixed, a second continuity test was performed to verify the fixes.
II. Component Soldering
Each component was hand soldered to the board. Issues were discovered with the
designed footprints and labels that required modifications and noted in an updated design.
Noted in the Figure below are the specific footprints and labels that needed
modifications. The errors in the footprints are a direct result of non-standard sizes that
needed to be created in the PCB design software by hand. Each component is numbered
in Figure 1 and their issues and repairs are listed below.
P13036 – Notification Alert System
PCB and Soldering Notes
Elizabeth Phillips
Figure 1: PCB with Noted Issues
1. MAX1758 – Footprint was too small. The metal connections on the chip were slightly
trimmed so it could fit properly and then soldered on using a heat gun.
2, 3, 4. FAST, FULL and FAULT LEDS – Footprints were too small. The FAULT LED
could be soldered on by scraping away the top layer of the PCB to extend the footprint.
The FAST and FULL LEDs were soldered on using wires.
5. 1M labels – Should be 10k labels and noted on final design.
6. LM339 – Footprint was too large. Scrapped away the top layer of the PCB on the right
side of the chip in order to extend the footprint. The ground pins were then soldered to
the exposed copper while the pins that needed to be floated were pulled up away from the
board.
7. 22 µH inductor – Footprint was too small. Soldered a small wire that would connect
the trace under the inductor. Afterwards, soldered a wire to the inductor on one side while
soldering the other side to the footprint. Protected the traces under the inductor with
electrical tape.
8. 0.05 Ω Sense Resistor – Footprint was too small. Scrapped the top layer of the PCB to
expose the copper. Soldered the resistor to the extended footprint in order to function
correctly.
P13036 – Notification Alert System
PCB and Soldering Notes
Elizabeth Phillips
9. EMF Diode - – Footprint was too small. Scrapped the top layer of the PCB to expose
the copper. Soldered the diode to the extended footprint in order to function correctly.
10. Alert LED board – After initial case was designed, it was determined that the spacing
between the LEDs needed to be wider. Removed the PCB board and created a new board
using extra green board, the Alert LEDs and through-hole 100 Ω resistors.
III. Functionality Testing
The entire PCB board continuity was retested after the components were soldered
on. Once passed, the board was broken down in sections to be tested. These sections
included;
a. 5 V Regulator Circuit
c. Alert LEDs
e. RPi 5V
g. On/Off Switch
i. 12 V Motor Connector
k. Fuse
m. Battery Charging
o. MAXIM to Regulator Circuitry
b. Indication Circuit
d. LED NMOS Switch
f. 12V Power Connector
h. Shaker Switch
j. MAXIM LEDs
l. Snooze Button
n. Battery Discharging
IV. Debugging
Plugging in the board resulted with resistors exploding which immediately halted
testing. Since the resistors were connected to the MAXIM chip, testing occurred on rest
of the board. Each issue found and the proper method to fix it is noted below.
1) Green LED on the indicator circuit had to be replaced because it was not bright
enough. Replaced with a through-hole LED of similar characteristics.
2) NAND gate on indication circuit was floating even when grounded. Had to
connect a wire from the GND of the chip to a known working ground.
3) FULL and FAST LEDs had to be removed since placed on the wrong direction.
During removal, footprints were ruined and thus, could not be used. Still able to
check the voltage levels of the LEDs with voltmeter.
4) TPS5420 chip was accidentally created on the schematic as the mirrored image in
order to make things easier for drawing. This layout was then transferred to the
PCB and caused the designed to be wrong. Had to flip over the regulator chip and
pull the connecting leads to the other side before soldering upside down.
5) When the shaker switch was enabled, entire circuit would turn off. EMF diode
was soldered backwards so it was then placed in the correct direction. However,
the diode soldered in its place was a Zenar diode which then needed to be
replaced with a regular diode.
6) FAULT LED had to be removed completely because the board was designed
such that the entire trace was grounded. The trace had to be cut with an blade and
a wire was used to connect the two B- points together to bypass the issues.
P13036 – Notification Alert System
PCB and Soldering Notes
Elizabeth Phillips
7) 10k resistor on Pin25 of the MAXIM chip had the pads shorted to ground. Had to
directly connect the resistor between the 1000 pF capacitor to the 0.1 µF capacitor
to bypass the issue.
8) Accidental connection point between Pin 25 and D3 on the MAXIM chip. Needed
to remove the diode from the circuit and soldered it between Pin 25 and a wire to
the correct connection point. Used electrical tape under the diode to protect other
traces.
9) 0.1 µF capacitor between D3 and Pin 20/Pin 22 was misplaced due a schematic
error. Soldered the capacitor on one part of the pad and the other to a wire that
connected the component to the correct point for the board.
V. Results
Once all the issues were fixed, the blown up resistors were replaced and then the
circuit was powered on. Each section was then tested in order to verify full functionality.
All issues and changes that were founded were then fixed in the PCB design and the
corresponding schematics.