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Building up a Power Switch
Needed Parts and PCB
You need a PCB. You may use the layout from Github and etch it yourself or order the PCB or a complete kit.
Partlist (in buildup order)
Buildup of PCB
As always: start from flat to high. Go through the partlist and solder the parts from the top ones to the last ones.
For some parts, you have to consider something special:
IC holder: Look at the notch and place it in the right direction.
Solder it to a wire if you want to place the PCB in a housing later. Read the instructions on how to solder the LED to a cable
. The longer wire of the LED is +. It goes into the hole more in the middle of the PCB.
ISP Connector: The notch points to the side of the PCB (towards the voltage regulator).
10 uF Capacitor: The marked line is -, which points to the LED. On the PCB, + is labelled.
ATMega: Before inserting it, you may want to check the voltage levels when switching the power on. Pin7 should have VCC (3V) against pin8 (ground). If you have different voltages: don't panic, nothing is broken, nothing is fried. Search your error. To insert the ATMega, bend the pins at 90 degreed by placing the ATMega on the table and bending it carefully. Then insert it into the IC holder. Be sure that you are not charged with electricity (ESD!) when touching the IC pins.
You should also check the voltages first before soldering the module. At the place for the radio module the pad beside the antenna and at the opposite side the third pad should read about 3.3 V. For soldering, read the RFM12B mounting instructions
Relais: If you want to switch high currents, especially at high voltages, it is recommended to solder the wires directly to the relais pins on the bottom of the PCB.
(Image directly loaded from external GitHub source. If it doesn't work, fix link in wiki!)
Flashing the firmware
If you have a new ATMega where nothing is flashed onto, download a prebuilt binary package or build your own firmware. If you bought a hardware kit, the ATMega should already be flashed.
After flashing and switching the power on, your power switch should blink three times slowly. If you haven't flashed working EEPROM settings, it flashed quickly endlessly.
In normal operation, the LED shows the status of the relay. If a timeout is counting down, it flashed very shortly once a second to indicate this.
Integrate it into a housing