My Ideal sensor node PCB

[Bandra]

Just for completeness, my PCBs came in and I've had a chance to solder them up. The PCBs are really nice. iTead have done a great job. @Zeph, turns out that I didn't need to cut my PCBs because the friendly folk at iTead cut them for me.

Here's a photo of a few things soldered on:

Underneath the APM I have a 1M and 470K resistors for the battery voltage check. There's also a 4.7K resistor for the Dallas DS18B20 temp sensor. Finally there's a 4.7K resistor for the LDR divider circuit.

You can also see the 4x2 header for the radio, the LDR itself, and the 3.3v step-up converter.

Here's the (almost) finished package:

You can see all the exposed solder pads for my various sensor configurations (motion, humidity, baro pressure, door reed switch, distance and soil moisture).

The range on the nRF24 is fine. I put my gateway at one end of the apartment and it easily picked up my sensor at the other end of the apartment (about 10m away through two thick internal walls). So I'm not worried about the nRF24 being parallel to the GND plane.

I actually took off the 4.7uF cap. It's probably my PCB (don't think the auto-route did a great job of it) but it made the radio flaky. Works just fine without it.

Now to find a box to put it in...

[hek]

Nice @Bandra!

[marceltrapman]

@Zeph said:

Have a look at this little fella: http://www.digikey.com/product-search/en?mpart=W25X40CLSNIG&vendor=256

Interesting but even when I am willing to stock them up (50 pcs) the shipment costs exceed the price of them :(

[bjornhallberg]

@marceltrapman Have you looked at AliExpress? Seems they had a few sellers offering this chip.

[marceltrapman]

@bjornhallberg said:

@marceltrapman Have you looked at AliExpress? Seems they had a few sellers offering this chip.

I never considered them. Took the plunge for a little less then 0,19 EU per piece :)

[Zeph]

@marceltrapman said:

@Zeph said:

Have a look at this little fella: http://www.digikey.com/product-search/en?mpart=W25X40CLSNIG&vendor=256

Interesting but even when I am willing to stock them up (50 pcs) the shipment costs exceed the price of them :(

Sorry. The problem with 4 Mb chip is that it's so cheap one feels bad about the shipping cost! :-)

I was also looking at some 128Mb (16 MB) flash memories at $2.78, where the shipping would be a smaller part of the order

More seriously, I hope the Ali Express order works well.

[RJ_Make]

@Bandra Looks fantastic! I'll take 3 :-)

[Bandra]

@ServiceXp
Thanks mate! I've soldered up 3 of the boards now and they're all working fine.

So far I've made one just with temp and light. One with temp, light and humidity, and one with temp, light, humidity and pressure. I'll make one more tonight that will just have temp and soil moisture.

I'm not entirely happy with the two caps at the bottom of the board. The auto-route feature of Eagle is good, but I don't think it quite got that right. Seems to run fine without the two caps so the PCBs are not a write-off.

I've got way more boards than I need. So I'm happy to send 3 off to you. PM me your address.

[marceltrapman]

@Bandra said:

I'm not entirely happy with the two caps at the bottom of the board.

What is it that you are not happy about?

Trying to learn here because I am still not sure if I will just make my boards myself or keep it with one or two prototypes and use iTead as well...

Talking about iTead, I saw that they can also check your board, did you decide against that?

[RJ_Make]

@Bandra Thanks, I sent you a PM... I think.. I used the "Chat" system... ;-)

[Bandra]

@marceltrapman
The auto-route feature in Eagle attempts to make the most efficient board layout it can. To do that, it seems to join the traces where ever it can. When you click on the rats nest button, it will combine any GND traces that it can. Since the cap sits on GND, for example, it assumes it can put it anywhere on a GND trace, and physically dislocates it from the radio pins. I just noticed that on my board, for example, the nRF24 cap doesn't sit directly across + and -.

So my next go I would manually route those traces first then auto-route the rest.

It's no big deal, because if I get bad reception then I can always solder the decoupling cap directly onto the radio.

I did choose the option to check my board. It's my very first PCB (which is why I didn't pick up the problem) so I was expecting for them to find lots of problems. But it turns out that technically my board is correct. It's the "logic" of the board that's wrong, so iTead could not have picked this up.

Lesson learned!

[marceltrapman]

@Bandra Aha. Thank you for the explanation.

I don't use auto-route at all. Sometimes I check it out, when I am tempted to try to avoid my brains doing overtime at finding a new route for yet another trace, but I always undo it.

[jribera]

Is anyone with a tested and working sensors PCB willing to share the design files ? This way people can order directly from oshpark, iteed etc. I'm sure these will make a great addition to the mysensors.org website.

[Dvbit]

Hi
I would also benefit from the sharing on OSHPark or similar sites as I am a total newbie.

Btw thanks to all the pros for their great work ;-)

Bandra your design is for now the one that gets closer to my desires. Really nice compact and flexible

[ToSa]

@Zeph said:

Have a look at this little fella: http://www.digikey.com/product-search/en?mpart=W25X40CLSNIG&vendor=256

Any proposals for DIP-8 flash to use for breadboard testing that are compatible to avoid surprises when switching to the SOT-8 ones later-on? Do all of these SPIflash chips use the same "protocol"?

[Zeph]

@ToSa

Here's a dip version of the next larger brother from adafruit:for $1.95 https://www.adafruit.com/products/1564

Then digikey has the soic for $0.43
http://www.digikey.com/product-search/en?x=0&y=0&lang=en&site=us&keywords=W25Q80BV

(Digikey has listings for the dip version but 0 stock)

I have not used these so I don't have any first hand recommendation. I cued in on this line because Felix uses the 4Mbit version on the Moteino, so I looked it up and thought it looked good.

(The Anarduino uses a 128 Mbit spi flash chip from a different line).

[ToSa]

@Zeph
What I don't like about Flash is the need to erase before writing / the ability to erase only full sectors (4k if I get it right from the WB datasheet). Not a big deal for bootloading or logging where you can erase all upfront but limits the use-cases.
What I really like is that a lot of the SPI Flash chips and EEPROM chips have the same pinout - which means depending on the specific need you can use a flash or an EEPROM using the same PCB layout (example EEPROM that allows single byte writes without erase: 25LC256 - obviously less memory and higher price but serves different purpose - 256kbit for <1€)

So I really like the idea of having this added to the PCB layout - especially because it can serve different needs depending on what chip is selected :)

[Zeph]

@ToSa
Yes that flexibiity is attractive.

I don't have the datasheets right here, but...

Do I recall that there's often a way to test for the type and size of chip (that's actually installed) using SPI?
Do I recall that some include a unique ID?

(I might be thinking of the 128 Mbit chip used by anarduino)

For bootloading one attraction is the possibility of letting application code fill and verify the external Flash using the full normal protocol (at the cost of some space in operational PROGMEM), then having a relatively simple boot-loader to transfer it to PROGMEM The sensor can continue to operate while packets are written to external flash, using high or low portions of the wireless bandwidth. When the application has finished loading and verifying the new firmware in external flash, it would write a "All OK, use this" signature to the external flash and reboot; the bootloader would notice that signature and copy from external flash to application PROGMEM.

In this case, the bootloader doesn't need to have a radio library or MySensors protocol stack (even trimmed down), and so there's no need to change the bootloader when the OTA protocol changes, eg MySensors 1.3 vs MySensors 1.4 vs RadioHead. Pretty much all the hardware config the bootloader would need is the select pin for the SPI flash. And if you were using a low bandwidth network (eg: 433 Mhz at 38400 bps) you could take as long as it needs to sent out firmware packets mixed with ongoing normal operation, before doing a sudden reboot/bootload.

That said, not every node is going to have external flash, so I'm happy to have the alternatives of your approach which doesn't require it.

[meanpenugin]

Bandra,

Any chance we can get the files to order our own?

If I want to use this with a 5V regulated supply, how hard would it be to add a 5V-3.3V converter for the Radio?

Edward

[Bandra]

Thanks for your interest, guys!

My PCB is getting really close, but I'm not entirely happy with it. I've made up 5 of them and scattered them around my place. For the most part, they're working well. However I have the following issues:

• The battery voltage varies. I don't think my cap is quite doing the job, so I may need to tweak the PCB to get it closer to the voltage divider. I'm running Domoticz and it does a good job of averaging the battery level out, so it's not completely bad, but I'd really like to fix it in the next version of the PCB.
• My moisture sensor (the one from the MySensors store) doesn't work very well. It chews the battery (cos the sensor from the store has 2 leds on it, plus it's always "on". I'll pop those off and see how it goes. However I think I can do the moisture sensor better. I'm thinking of including another voltage divider, and run the sensor off the digital pin for power. That way, I can power the sensor down in between samples.

I think that I can also include my own step up voltage converter. I'm not entirely happy with the chinese step up converter. So far my 2xAA batteries have lasted several weeks, and they're still going strong, but I suspect that I'll only get a few months out of them. I'm aiming for a year.

I'm designing our new house at the moment, which is taking up a lot of time, but I'll get onto rev 2 shortly. Once I'm happy with it, I'll put the design up here so that you guys can get your own made up.