Print PDF
Favorite
Email
Step 2The circuit-layout
The ULN2803A is a darlington-array, consisting of 8 individual darlington-drivers with suitable resistors on the input-side so that you could directly connect the output from the microcontroller to the input of the UNL2803A. If the input gets a high level (5V) from the microcontroller, then the output will be connected to GND. This means that a high on the input will light up the respective LED-strip. Each channel might be used with a current up to 500mA.
Standard ultrabright 5mm LEDs normally use 25-30mA per strip and even eight of them will stress the FET only with 200-250mA, so your far away from any critical points. You might even think about using high power 5W LEDs for the wakeup light. They usually use 350mA at 12V and might also be driven by this array.
The pushbutton "S1" is the reset-button for the microcontroller.
The switch "S2" is the selector of sunset or dawn. You could also replace it by a pushbutton and activate sunset by an interrupt in the software.
The potentiometer R11 acts as a selector for speed. We use the picaxes ADC ability to read out the position of the potentiometer and use this value as the timescale.
The picture shows the first board that I built with 7 individual transistors (BC547C) and the resistors to drive them. I didn't have the ULN2803 at the time I build the circuit, and now I'm missing some other parts. So I decided to show you the original layout, but also provide the layout with the new driver-array.
Standard ultrabright 5mm LEDs normally use 25-30mA per strip and even eight of them will stress the FET only with 200-250mA, so your far away from any critical points. You might even think about using high power 5W LEDs for the wakeup light. They usually use 350mA at 12V and might also be driven by this array.
The pushbutton "S1" is the reset-button for the microcontroller.
The switch "S2" is the selector of sunset or dawn. You could also replace it by a pushbutton and activate sunset by an interrupt in the software.
The potentiometer R11 acts as a selector for speed. We use the picaxes ADC ability to read out the position of the potentiometer and use this value as the timescale.
The picture shows the first board that I built with 7 individual transistors (BC547C) and the resistors to drive them. I didn't have the ULN2803 at the time I build the circuit, and now I'm missing some other parts. So I decided to show you the original layout, but also provide the layout with the new driver-array.
7-Strip Sunset Lamp.sch259 KB| « Previous Step | Download PDFView All Steps | Next Step » |
1
comment
|
Add Comment
|
May 26, 2010. 3:01 AMfloodll
says:
Wow, step two went by pretty fast.
Reply
 |
Add Comment
|
