|1||PCB RGB Dimmer 1|
|4||Resistor 560R green-blue-brown||R1-R4|
|1||Resistor 1M brown-black-green||R5|
|1||Voltage regulator LP2950Z||IC3|
|1||Connector AVR ISP 6pin||JP1|
|1||Connector pin header (for serial TX debugging etc.)||JPx|
|1||Transceiver PCB RFM12B||IC2|
|1||Antenna (82,2mm wire)|
You have to decide on the LEDs you want to use. Depending on the type, you have to use different resistors R6, R7, R8 for the LEDs. See further down for a recommended one.
The capacitor C2 is only to buffer the input voltage in case you connect LEDs that draw much power and you want to avoid problems with some programmers that may have problems flahing when the voltage changes much.
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:
(Image directly loaded from external GitHub source. If it doesn't work, fix link in wiki!)
The device has an internal voltage regulator with 3.3V output to power the ATMega and the RFM12B. It's recommended to power the whole device with a 5V power supply. You can use a cheap one that is meant as phone charger. They have typically 500mA output current.
You can power three single LEDs or a multi RGB LED with common anode (+). The maximum current is 0.6A, limited by the transistors. Calculate the resistor you need by the following formula:
R = (U_in - 0.3 - U_LED) / I_LED
with U_in the input voltage of the device (e.g. 5V), U_LED the voltage your LED needs (e.g. 2.8V) and I_LED the current you want to do through the LED (e.g. 250mA).
One LED type that is very bright with a moderate current are the Cree XP-E LEDs. They are available as a module in the smarthomatic shop. The module makes assembling easier and ensures good cooling.
If you use this module, the following sets of resistors are recommended:
|R6||Resistor for red LED||39 Ohm||27 Ohm||7,5 Ohm|
|R7||Resistor for green LED||27 Ohm||18 Ohm||5,6 Ohm|
|R8||Resistor for blue LED||22 Ohm||15 Ohm||3,9 Ohm|
The “normal” resistors are enough if you use a thin glass housing (as shown on the homepage). You can use normal 1/4 W resistors and the LED module won't heat up much. No heat sink required. This is the safest and easiest choice.
The “bright” resistors result in LED currents of ~120mA and a power dissipation at the LED module of ~1W. It should not need an additional heat sink, but it gets hot already (you can touch it, maybe ~50°C). The resisors have a calculated power dissipation of ~0,3W. 1/4W resistors max be enough, but I recommend to use metal oxyde resistors (1W). The overall current of the RGB dimmer is 380mA, so a typical power supply for smartphones with 500mA max. current fits perfectly.
With the “max” resistors, you definitely need an extra heat sink at the LED module and resistors which can cope with the higher current (1W).
Use resistors which can tolerate the power they consume. The power is calculated as:
P = U_Res * I_LED
with U_Res the voltage at the resistor.