Open Access Mega Kit - Build Instructions
Open Access Mega v3 Build instructions
Overview
The Open Access Mega kit requires surface-mount soldering of approximately 75 0805 pitch components. It is recommended that first-time builders practice on smaller board to get the technique down prior to building. There are several excellent tutorials on-line, including:
You will need a quality temperature-controlled soldering iron for the non-SMT components, a hot plate or toaster oven for reflowing, a small squeegee or bondo scraper from the auto parts store, and a sheet of glass or plastic to tape the PCB/stencil to. A Mylar solder-paste stencil is included in the kit.
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
Detailed Instructions
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)
- PTC Fuses (No polarity, 200ma, 15V (Markings:C)
- Reader power lines (F2,F3)
Integrated circuits
- 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, stripe towards right side of PCB)
- 33uF, 16V
- (C2, polarity strips towards top of PCB)
Inductor
- 150uH (L1, no polarity)
Crystal (observe polarity/pin 1 mark)
- 32.768Khz RTC crystal (Q1, dot towards bottom of PCB, chisel-point towards top)
Switch
- 5mm tactile switch, NOT reflow solderable.
- Place and sodler 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 inouts (16 and 24 pins,) you may need to trim the right edge of each pin header with a sharp pair of cutters to make them fit. 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 Etherent 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 on the relays, as this may damage them. Dry the PCB and prepare for testing. Install the Lithium battery, (+) side up.
Testing and burn-in
1. Begin by applying 5-8V to the power input connector (X35). The green power LED should light. Measure the voltage at the +5V terminal on the Arduino header. It shoudl read 4.9-5.1VDC. Increase the voltage to 12-14V. The power reading should be the same. If your power supply measures current, the idle board should be drawing less than 100ma. If there is no voltage present, disconnect power immediately and feel for any hot components, especially on the power supply circuit. This is often caused by a short or resistor/chip installed backwards. 2. Install an Arduino Mega (standard or 2560) and power up the board again. Compile and upload the latest code, uncommenting the "hardwaretest();" line to make it start in self-test mode. Connect voa serial at 57,600, 8,N,1. After it boots, verify that all relays click on and off, and try shorting each of the 2 reader input (D0/D1) and the 16 analog inputs to ground, one by one. They should all go from >200 to <50 if shorted. A diode install backwards or a short is usually the cause of trouble here. 3. Comment out the self-test and boot the Arduino into regular mode. Connect via serial and hit (?) to see a menu. Make sure your terminal is set to send a <CR> after each line. Hit 'e 124' to enable privileged mode with the default password of 1234. Set the time and verify that the clock holds the time between reboots and power-off. Connect up a reader to the reader inputs and try swiping a card. After 1-2 swipes (it may pick up nosie from inserting the connector), it should give a consistent value. Be careful to hook up the '0' and '1' lines correctly. If they are reversed, all card readers will be inverted. Add a card at position 1 or higher, using this command "a 1 254 1f23b6" or whatever card number you swiped. The security level "254" is the default that will open all doors and does not have a time restriction. When you swipe that card again, you should see one relay click on for 5 seconds and then off again. Repeating the scan at the second reader should do the same for the second door relay. Two other relays are configured by default for a door chime and siren. The remaining 4 relays can be configured for custom applications, such as signage, lighting, etc. 4. Hit command '3' to train the alarm sensors. This will measure the analog voltage at each of the 16 sensor inputs and store the value to eeprom. When you install alarm sensors, you will want to repeat this procedure again to get the "not activated" or "doors closed" values stored. 5. Optionally, burn in the system by leaving it plugged in for 24 hours prior to use in production. You can configure the hardware test for 100-200 iterations for a stress-test.