Open Access Mega Kit - Build Instructions
Open Access Mega v3 Build instructions
The Open Access Mega kit requires surface-mount soldering of approximately 75 0805-pitch components. It is recommended that first-time builders practice on a smaller board to get the technique and reflow times sorted prior to building. There are several excellent tutorials on-line, including:
Required Tools & Materials
- Quality temperature-controlled soldering iron
- Optional: hot-air station for reworking mis-placed components
- Solder (rosin or water-clean) for through-hole components
- Desoldering braid for fixing mistakes
- Hot plate or toaster oven for reflowing
- Small squeegee or bondo scraper for applying paste to the stencil
- Sheet of glass or plastic to tape the PCB/stencil to. A Mylar solder-paste stencil is included in the kit.
- Sharp tweezers for placing parts
- Flush cutters for trimming leads on through-hole parts
- Alcohol for cleaning PCB and removing excess paste
Solder paste is available at reasonable cost from these suppliers:
Zephyrtronics - Distributors of SMT rework supplies
Advanced Precision - Excellent prices and selection of solder materials
1. Begin by laying all of the components out on a clean surface and identifying/organizing them. When ready, clean the PCB with alcohol and stencil on the solder paste.
Clean up excess with more alcohol.
2. Place components with a fine pair of tweezers, working from smallest to largest. If tweezers begin sticking to part, clean as needed with a soft cloth or paper.
Some excess solder paste is OK, as it will reflow down and likely not bridge. Bridges can also be fixed later with a fine soldering tip and desoldering braid.
Place the components as follows:
Resistors (no polarity)
- 2.2K, 5% (Markings: 222)
- All reader and analog input signals (R16-19,R23,R26-28,R35,R37,R38,R39,R43,R45,R46,R53-54,R60,R62).
- All LED resistors (R7-15).
- Reader output signals (R54, R55, R32, R63,R64,R68)
- 10K, 5% (Markings: 103)
- All analog signal pull-up lines (R20-22,R24,R29-31,R25,R40-42,R36,R48,R49-50).
- Voltage divider for 12V monitor line ( R47,R71-73).
- All reader pull-ups (R56,R57-58,R52,R59,R65-67,R61,R69)
- 150 Ohm, 5% (Markings: R150)
- RS-485 termination resistor (R73)
- Reset jumper resistor (R76)
- 10 Ohm (Markings: 100)
- Reader cable shield terminal resistor to GND (R74,R75)
- 4.7K (Markings:472) I2C Pull-ups (R33-34)
- 10K, 1% (Markings: 1002)
- Power supply divider resistors (R1-R4)
- 0.15 Ohm (Markings: .15)
- Power supply current (R5) (Critical, don't mess this up!)
Small capacitors (no polarity)
- 0.1uF ceramic (no marking, check package or strip for value)
- Decoupling caps (C4,C5,C8)
- 200pf ceramic (no markings)
- Power supply cap (C3)
Diodes (observe polarity stripe on end)
- 1N5819 Schottky Diode (Markings: 75 or various)
- Power supply diode (D1, stripe away from GND, i.e. towards the power supply IC)
- 5.6V Zener Diodes (Markings:CV or various)
- All input lines (D4-D18, D20-29, stripe is towards outside edge of PCB) (D19, stripe is towards the right side of PCB)
- In all cases, the stripe is oriented AWAY from ground.
- Reverse protection diode (Large, markings vary)
- (D2, stripe towards top of PCB)
- Bi-directional TVS diode (Large, only diode with no polarity stripe)
- (D3, polarity doesn't matter)
- Light Emitting diodes (LEDs)
- In all cases, the arrow or pointy part of the 'T' should point towards (-)
- PTC Fuses (No polarity, 200ma, 15V (Markings:C)
- Reader power lines (F2,F3)
- SN65HVD05 RS-485 driver
- (IC1, stripe goes down when looking at board from top)
- MCP34063 buck power regulator
- (U$1, stripe goes to the right of PCB)
- ULN2803 8-channel driver array
- (ULN1, pin 1 mark goes towards top left of PCB)
- AT24C 128KB EEPROM
- (U3, pin 1 mark goes towards bottom right of PCB)
- DS1307 real-time clock IC
- (U$7, pin 1 mark goes towards bottom left of PCB)
Electrolytic caps (observe polarity stripe)
- 100uF, 25V
- (C1, polarity stripe towards right side of PCB)
- 33uF, 16V
- (C2, polarity stripe towards top of PCB)
- 150uH (L1, no polarity)
Crystal (observe polarity/pin 1 mark)
- 32.768Khz RTC crystal (Q1, dot towards bottom of PCB, chisel-point towards top)
- 5mm tactile switch, NOT reflow solderable.
- Place and solder by hand AFTER reflow. (Next to JP2)
3. Finish placing all parts and straighten as needed. Reflow solder using hotplate or oven, using an appropriate process.
4. When PCB is cool, inspect the SMT parts under magnification and hand-solder dry joints or remove excess solder from shorted pins as needed.
5. Begin soldering the 3.5mm pin headers. For the relay and analog/alarm inputs (16 and 24 pin headers,) you will need to trim the right edge of each pin header with a sharp pair of cutters to make them fit end-to-end. Use the plugs to hold and align them while soldering. Tack down 1 pin on each and make sure they are fully seated before soldering the rest.
6. Solder in the MOV (R6). It has no polarity. Put the fuse into the fuse holder clips (F1) and solder it from top and bottom.
7. Solder in the battery holder, observing the polarity marks and part outline on the PCB silkscreen.
8. Install all 8 relays. Use tape to hold them in position, and tack down 1 pin each to make sure they're seated all the way before soldering.
9. Install the 5mm power terminal (X35).
10. Install the Arduino pin headers. Use an Ethernet or other shield to aid alignment from the top if desired.
11. Inspect all joints and correct any problems. Clean the PCB with alcohol or flux remover and a toothbrush. Get rid of flux and any solder balls. All components are sealed and will not be damaged by aggressive cleaning. Do not use an ultrasonic cleaner, as this may damage components. Dry the PCB and prepare for testing. Install the Lithium battery, (+) side up.
Testing and burn-in Instructions
When you've completed assembly or have installed a new board, use the following procedure for initial testing.
Open Access Mega Testing and burn-in