Table of Contents
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)
| Amount | Part | Placing | Picture |
|---|---|---|---|
| 1 | PCB Power Switch 1 |  |
|
| 2 | Diode 1N4148 | D1, D2 |  |
| 2 | Resistor 560R green-blue-brown | R1, R2 |  |
| 1 | Resistor 1M brown-black-green | R3 |  |
| 1 | IC holder | IC1 |  |
| 1 | Voltage regulator LP2950Z | IC3 |  |
| 1 | Transistor BC547C | T1 |  |
| 1 | LED 2mA | LED1 |  |
| 1 | Connector AVR ISP 6pin angled | JP1 |  |
| 1 | Connector Switched Output 3pin | X1 |  |
| 1 | Connector 1 pin header (for serial TX debugging) | JP5 |  |
| 1 | Capacitor 10µF | C1 |  |
| 1 | Capacitor 1µF | C2 |  |
| 1 | IC ATMega328 | IC1 |  |
| 1 | Relay FTR-K1C (230V, 16A) | K1 |  |
| 1 | Transceiver PCB RFM12B | IC2 |  |
| 1 | Antenna (82,2mm wire) |  |
maybe extra pins, at your opinion.
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.
- LED: 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.
- RFM12B: 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
describe it…
Modification of RFM12 power pin (PCB < V1.1)
In PCBs >= V1.1, the RFM12 power pin is connected to an ATMega I/O pin to make it possible to restart the transceiver if communication fails.
If you want to modify your old PCB version to have this feature as well, cut two traces carefully (marked red in the picture) and connect two pins of the RFM transceiver to the ATMega (marked green in the picture).
Make sure you don't create a short circuit and cut the traces correctly. Use a multimeter to check this.
