vrijdag 27 december 2013

Ordered PCBs

Normally, one of my friends etches the PCBs I design, but there are limits on how small you can make traces on those (and i'm pretty sure he got sick of drilling hundreds of holes every time). So about a month ago I re-designed some of the PCBs to have them made in China, and they finally arrived today!

I chose the "10pcs 10x10cm" option at iteadstudio, and I really wanted to take full advantage of the 100 square centimeters per board, so I tried to make everything as small as possible, while still using through hole components. The first thing I really wanted to have were some boards for the atmega328 microcontrollers. The one I designed to be etches by my friend were okay, but had were some flaws / things that could be improved: 

The crystal didn't really fit, the voltage regulator heatsink blocked the reset button, I never actually used the reset button, it didn't have enough 5v en 0v pins available, it didn't have leds for the Tx and Rx pins, and it used some jumpers, since it was single sided.

It took a lot of time to get the new design small while still having all the extra's on it, but I managed to squeeze it all down to the point where I didn't have a single bit of unused space on the pcb. 

To get it this small, I dumped the reset button all together, replaced the 5mm LEDs for small rectangular LEDs, put as much as possible underneath the chip itself, and used a 3mm "Polar" LED for the Rx/Tx. This it an LED with two oppositely connected diodes in it, and I wired it so when Tx is high, and Rx is low, it lights red, and when Tx is low and Rx is high, it lights green. Two leds for the price of one!

Another chip I use a lot is the 74hc595 shift register, and while the original etchable design I made for them was fine, I liked to have a professionally made version aswell. (I did add some capacitors and screw holes in the new design, but didn't change anything else.)

Apart from the shift registers there are some transistor arrays on the PCB. I use these when driving led strips, like in the "light boxes" and the modded IKEA light, but you can also solder resistors in place of the transistor arrays for driving simple LEDs. Another nice feature of these prints is that by placing the headers, you can choose between grouping the outputs as 8 | 8 | 8 or 9 | 6 | 9. The lather is usefull when using RGB LEDs, because then you can simply use eight 3-pin connectors. 

At the edge of the 10x10cm PCB I had some space left, which I used to make some "led strip connector PCBs", just a small strip where you can solder pieces of led strip on to connect them together. This makes a nice 2.3W RGB LED.

After soldering one board of each kind I strapped them all together; they do their job like chinese factory workers!

The metal plate is from another IKEA light I'm modding, but it's still a work in progress...

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