Yet another PCB to address (nearly) all Arduino pins

[phil83]

Hi everyone,

after I had my first PCB manufactured last year in China, I'm a little bit addicted to designing and soldering new boards so here's another idea for a universal board. I'm building my own reflow oven right now, so I will try to directly use smt parts without using an arduino pro mini on top of my board.

The scheme looks like this:

I added as many parts as possible and tried to make nearly all other pins for Arduino accessible with some 1.25mm pinheads. Here's a list of all the pins and where you'll find them:

Arduino Pin/ Function/ Pinhead
0/ RXI/ not used
1/ TXO/ not used
2/ D2/ NRF24 / Pinhead 2 / Button (via jumper)
3/ D3/ Pinhead 1
4/ D4/ Pinhead 2
5/ D5/ Pinhead ISP
6/ D6/ ATSHA
7/ D7/ LED
8/ D8/ 25AA256
9/ D9/ NRF24
10/ D10/ NRF24
11/ MOSI/ Pinhead ISP
12/ MISO/ Pinhead ISP
13/ SCK/ Pinhead ISP
A0/ A0/ Voltage divider
A1/ A1/ Pinhead 1
A2/ A2/ Pinhead 2
A3/ A3/ Pinhead ISP
A4/ SDA/ Pinhead I2C
A5/ SCL/ Pinhead I2C
A6/ A6/ Dallas 14B20
A7/ A7/ LED

On the front of the board, there's the Atmega, an ATSHA, an EEPROM and a D18B20. on the back, I have two tactile switches and 3 LEDs, the idea is to drill holes in the box and access them from the bottom side while the additional sensors will be in front of the Atmega chip. Besides the ISP head for programming, I added some more digital lines to the ISP pinhead so the pinhead can also being used to connect to another serial device (with the digital pins being CS lines).
There are two connectors for connection to sensors etc and an I2C connector.

Size of the board would be 44.1x23.5mm.

What do you think of this layout? Is there any wrong connection regarding Arduino pins? Any ideas to improve the layout?

Many thanks for your input in advance,
best regards,
Philipp

[mfalkvidd]

That's a feature-packed board
Have you considered supporting the mysx connector?

[TD22057]

Looks very cool.

The immediate thing I noticed is that there should be bypass capacitors on all the IC's. So a 0.1uF cap on the crypto and flash memory chips. And if you have caps in the schematic, they should really be wired with the chip they go with. I noticed there are a few caps in the schematic that are by themselves (just vcc/cap/gnd) - if those are bypass caps, it helps a lot to have them shown in the schematic with the IC they go with. That makes it clear that they need to be on the board next to the IC and not at an arbitrary location.

Mounting holes for screws might also be a good idea.

[GertSanders]

A7 is an analog input only pin. So connecting a LED will not work. In the MySensor library the atsha204a is expected on A3.

[GertSanders]

Does the layout survive a design rule check ?

The pads of the 1.27" pinheaders seem very close to each other.

[phil83]

Hey guys,

many thanks so far, I will incorporate TD's ideas tomorrow.
For the A7, many thanks to Gert! Only A0-A5 can be used as digital pins so I will change this!
Design rule check was fine.

Thanks again and have a nice evening,
Philipp

[phil83]

So this could be an updates pin assignment:

Arduino Pin/ Function/ Pinhead
0/ RXI/ not used
1/ TXO/ not used
2/ D2/ NRF24 / Pinhead 1 / Button (via jumper)
3/ D3/ Pinhead 1
4/ D4/ Pinhead 2
5/ D5/ Pinhead ISP
6/ D6/ LED
7/ D7/ LED
8/ D8/ 25AA256
9/ D9/ NRF24
10/ D10/ NRF24
11/ MOSI/ Pinhead ISP
12/ MISO/ Pinhead ISP
13/ SCK/ Pinhead ISP
A0/ A0/ Voltage divider
A1/ A1/ Dallas 18B20
A2/ A2/ Pinhead 2
A3/ A3/ Pinhead ISP
A4/ SDA/ Pinhead I2C
A5/ SCL/ Pinhead I2C
A6/ A6/ Pinhead 2
A7/ A7/ Pinhead 1

What do you think?
Best regards,
Philipp

[tbowmo]

like @mfalkvidd asked.. Have you seen the MYSX connector? A "standardized" connector for mysensors platform..

https://github.com/mysensors-kicad/documentation/blob/master/TheMYSXconnector.pdf

[phil83]

Regarding the MYSX connector, I have seen the specification before but for me the 2.54mm pinheads are way to big since I wanted to have a really small board that I can also use for quite small sensors (window open for example). I changed some connections and came up with that scheme now:

I added the caps for the ICs, many thanks again for the hint!
Philipp

[phil83]

Hi there,

I had some more time to work on it and I rearranged the parts on the board. One question for me is how big to make the drill holes for mounting? Is 2mm ok?

I will clean up the silk screen writings the weekend and then send it out to China

Many thanks so far,
best regards,
Philipp

[TD22057]

You can find Eagle parts for M2, M2.5, M3 drill holes with tight and loose clearance in my Eagle parts library. I created the parts from this blog page.

[phil83]

Hi TD,
many thanks for the library, I incorporated the drill holes and it looks much better now!

Best regards,
Philipp

[vikasjee]

@phil83 said:

Hi TD,
many thanks for the library, I incorporated the drill holes and it looks much better now!

Best regards,
Philipp

HI Philipp,

Will you like to share your files with this final version of your PCB? This is an excellent stuff. Appreciate your design skills...

[GertSanders]

@phil83 If small is the target, use the SMD version of the NRF24L01+. Here is a small NRF24 library.

0_1456596545540_NRF24L01plus.lbr

[tbowmo]

@phil83

Nice board, but still would suggest MYSX.. It's got different variants, with more / less pins available..

I'm playing around with a boardlayout that's 18x30mm, with MYSX connector, and nrf24 (SMD) the NRF will protrude over one end of the board with ~5-7mm (Antenna area). so total length will be 18x37mm (or something in that area).

[TD22057]

One more tip: If you want to order a full 10x10 cm board, you can panelize them yourself and use https://github.com/p12tic/eagle-brd-merge to get around the 10x8 limit in the free version of Eagle. Worked great for my mother/daughter board order.

[phil83]

Hi all,
many thanks for all the valuable input!
I will share my files after having tested the board by myself for the first time!

@GertSanders: I've never thought about using the SMD version of NRF24L01, it really looks interesting!

@tbowmo: Your board size is really impressive, are you also using the EEPROM and ATSHA on that small size board?

The smallest and still (hopefully) manufacturable for me seems to be around 44x21mm...

Right now I'm waiting for all of the parts of my reflow oven, I have some boards for testing here and in case I'm successful with reflowing, I will order new boards in China.

Best regards,
Philipp

[phil83]

@TD22057: My dealer in China does some panelization for me as well, last time I ordered 20 board (size about 25x45mm) and I received 42... That was more than fine for me. But thanks for the link!

[tbowmo]

@phil83

It's complete with external flash (for OTA), atsha204, voltage regulator, 2 led's and a Si7021. Using 0603 smd components though.. (And it only got components on one side..)

Still working on some details, before publishing it though...

[phil83]

@tbowmo: Sounds very impressive, chapeau! I'm looking forward to seeing your design when it is finished!

[GertSanders]

@tbowmo I have been working on a similar board. The matter of external connections for switches and external sensors keeps me busy. The 1,27 mm spaced headers seem like a possible solution. But I have not found any female headers with wires (Dupont style) to go with the male versions. How do you solve the connection problem ?

[phil83]

@GertSanders: On aliexpress you can find sets of male and female 1.25mm connectors, do you think about something like that:
http://de.aliexpress.com/item/20sets-Micro-1-25mm-5pin-Cable-JST-1-25-5-Pin-Male-Female-Connector-plug-with/32464250609.html?spm=2114.010208.3.2.BMcTZF&ws_ab_test=searchweb201556_9,searchweb201644_5_505_506_503_504_301_10020_502_10001_10002_10017_10010_10005_10006_10011_10003_10021_10004_10022_10009_10008_10018_10019,searchweb201560_2,searchweb1451318400_-1,searchweb1451318411_6448&btsid=8ded8c25-db33-49ed-835b-307cb83c0f47

[phil83]

As I read your post again, you mean something like this:
http://de.aliexpress.com/item/5-sets-Double-Row-Female-Socket-SMD-2-10-20pin-1-27mm-Pin-Header-connector/32542921161.html?isOrigTitle=true

[GertSanders]

@phil83 the micro connector set with the wires is a very good suggestion. I will look around some more.

[phil83]

I finally went on with the project and received the pcbs last week... my soldering oven is running and I could finish the first board (still some parts are missing ) If only I had more time to work on that...
Here are some impressions:

I soldered some cables so that I can program it and check via ftdi...

More to come soon...

[GertSanders]

@phil83
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