Your comments are very welcome. I did not expect to get such a long and good explanation. I have a degree in electrical engineering and learned the basics of electronics in school 15 years ago. My career took a different path, I now work for an engineering company as a safety advisor.
Yesterday evening I soldered an LM2576 and the necessary components to a PCB and did some testing. I first attached a couple of leds, and measured almost exactly 5V powering it from my 25A lab power supply with only 7,2V. I then started attaching some 2W resistors till I got 2,5 amps out of the regulator. The voltage dropped a bit to 4,89V, which is still acceptable. So the cheap China inductor is up to the job I did not expect anything else as I did a lot of googling before I bought them. I found several people that have used the same inductors from ebay with the LM2576 regulator. The LM2576 can be found very cheaply, I paid 0.58$ a piece.
As for the board: I've decided to ditch the ICSP header as I will never use it. I don't have a programmer to connect to it. I only need the ftdi header to upload sketches and use the serial monitor. I've already bootloaded a couple of ATmega328's on my breadboard, which was very easy. I've also decided to leave out the led on pin 13 and the small inductor as it might cause more issues then do any good. I've added a ground plane to the top of the board and made most traces a lot wider, especially the VCC and AVCC connections. I've attached 100nF caps to both those pins. I'm going to leave all the big caps on the board. From experience I've seen that they are helpful when you power a lot of servos.
I've changed my design to a 2 layer PCB, was very easy in Eagle. Moved most of the traces to the top layer (red), so now the bottom (blue) is mostly ground. Made room for lots of caps, I'll do some testing with the board to see if it's necessary to put them all on. I have lots of electrolytic caps from decent brands, I'll will use the highest rated voltage ones that I have (35-50V) Those should be good enough. I only need to order the small 100µH inductor that's connected to the ATmega328P, all other parts I have. I'll have the board made by Seeedstudio (24.9$ + 8.1$ shipping for 10pcs).
Going to a dual layer board might be a good idea. Just need to find out how to make vias in Eagle. What kind of caps are low ESR and are available in 1000µF? I thought that only electrolytic caps are available in that size? I know these are high ESR and not the best suited for this application. I hope to power 12 small servos from the board for a quadpod (4 leg / 3 dof) or hexapod (6 leg / 2 dof).
This video shows 48 servos (I have the same servos) driven by a 3A 5V regulator, it's an LM2676 on an Mega1280 based board. I have the same board that I use in another robot. I thought why not make my own...
Thanks for all the comments. The board is single sided, I'm planning to have it made at Seedstudio or Iteadstudio. I'm going to reposition the regulator and retrace connections. I just had another look at the datasheet and can see my mistake. I bought 10 inductors on Ebay rated at 5A 100µH so they should be strong enough. I'm aware that servos are noisy things that's the reason for the big caps, the regulator needs a 1000µF cap on the output according to the datasheet. I'll add a diode across R1. Designing this board has been a big learning experience. I've spent hours reading datasheets and watching Eagle tutorials on Youtube
This is my first PCB design based on the ATmega328P. All components are through the hole, took me some time to make the board without any vias. The board has an LM2576 3A 5V switching regulator. The L1 inductor is a lot bigger then the outline on the PCB that's why there is so much space around it. I'm new to Eagle so I haven't bothered making a symbol for it. I already have most parts including the LM2576 regulator and 3A 100µH inductor. I have one issue though, the regulators that I bought don't have the pins staggered, they are all 5 straight. When I put the regulator on the PCB in Eagle using a TO220-5 symbol with straight pins I couldn't get it to pass a DRC check. Even after changing the TO220-5 symbol to the smallest pads. It always complains that there is not enough space between the pads. So I just used the staggered symbol and I thought of just bending the pins on my regulators Does my design look ok? Or won't this work? I'm a bit worried about the regulator, that's why I've put so many caps on the board. I have a decent stock of caps so I might as well use them... Datasheet of the regulator can be found here: http://www.datasheetcatalog.org/datasheet/nationalsemiconductor/DS011476.PDF
The board will be used for a couple of small robots using a bunch of small SG90 servos. With this design I can just connect the servos directly on the board. The regulator is powerful enough to power the servos. Power supply will come from a 2 cell Lipo battery.
Hi, I've been playing in Eagle 6.2 the last couple of days and made my own through the hole Arduino. I will use it to control a small robot, the board must power a couple of servos and sensors. I used a LM2576 5V 3A regulator that should be powerful enough. The schematic I have made is attached, can someone take a look at it and tell me if I didn't make any mistakes? In the schematic there is a small 100µH inductor (L2) connected between VCC and AVCC. I saw this in the schematic of the Arduino Severino, do I really need this? The board only has an ICSP 6 pin connector, can I use this to upload sketches? What programmer would I need to do this? Or are there other ways to upload sketches without removing the microcontroller? Are there programmers that I could connect to my board which I could use for the serial monitor? Do I need another/different header for this? This would help a lot for debugging code. I already have a couple of ATmega328P-PU's that I have bootloaded myself on a breadboard with an Arduino Duemilanove.
You need a resistor between the base of the transistor and the Arduino. Also take a good look at the code you have posted, it won't do what you want it to do... The leds will never turn because you immediately turn them of.