My Ideal sensor node PCB

[Zeph]

My thoughts on a standard room sensor:

This PCB board ($1 or so)
Arduino Pro Micro ($2.50)
nRF24L01+ ($1 or so)
passives and regulator
Box ($2-3)

Mounted to the front of the box: PIR motion detector, IR decoder (remote control receier), LDR light sensor. ($1.50 total w/shipping)

Mounted to the side: DHT-22. ($3 with shipping)

Other sensors as needed, with room for some expansion.

My idea is that I can send commands from any room with a handheld IR remote, and the central conrol will know what command comes from which room. So the IR detector (which is very cheap) is also standard.

If I get too many false hits on the motion detector, I might add an external pet-resistant motion detector from the alarm industry.

I wasn't aiming for boost, but if it's small and cheap and optional I might change my mind. One option is to use the $5 boost-only board Axilent was proposing, if I only rarely needed boost power. (I don't want to solder any microscopic chips myself tho).

Garage, attic, crawl space, water meter on the irrigation, etc would differ from this typical indoor room sensor, as would a clock module. I imagine some with wall power, some battery powered. Some boxes would be waterproof (really, just reasonably weather resistant).

I would have enough pins left over to drive an LCD display if I wanted one; character or graphic.

And this doesn't count the Christmas light control.

Some prices above assume buying around 10 or so, some do not. 3.3v APM is a bit more.

[therik]

@Bandra Exactly what I was going to do. Nice!

Question: Since pin D3 is in great demand (the only available intrupt pin for waking the pro-mini) how did you decide what sensors have access? I think only one sensor can connect to the D3 pin, right? I suppose the door reed switch sensor gets priority, or does distance get the D3 pin?

Right now I'm leaning to the PIR motion sensor getting the D3 pin. I think it's the only way to run a motion sensor off a 'sleeping' pro-mini, right?

Here is what I'm currently thinking...

From the bottom...a 2xAA battery pack, the pro-mini under the PCB in question, and a PIR, temp/humidity, and the radio. I'll break-out the other pins for some other things too, but this is the main function. I could replace the temp/humidity with the Dallas.

Thoughts?

[therik]

@Zeph I have a DHT-22 and my pin spacing is 0.1".

I was thinking of connecting the PIR and DHT-22 directly to the PCB and building a case around it. Of course, I could also use wires to remote the DHT-22 or PIR, but I like the option of direct connecting.

Oh yea, and where are you getting the DHT22 for $3? I need to use these due to the low humidity here in the desert. The DHT11 only goes to 20% and we a lower than that much of the year.

[therik]

@Zeph Oh yea, use a wet tile saw for slicing PCBs like butter, very smooth edge too.

[Bandra]

@therik
D3 is an interesting one. As you can see on my board, I've broken it out with a +'ve and -'ve and together called the 3 pins "motion". However, it's dead easy just to use D3 and either the positive or neg for the door switch (depending on whether I want a high or low switch (so it supports both normally open and normally closed).

The only drawback is, of course, (as you point out) that I can't run motion and door switch on the one sensor node. But that's ok. I've tried really hard to cram as many sensors onto each node, but the door switch sensors will just have to be dedicated. For the price of each node, I'm ok with that.

I like your layout. I was fearful of making the node too tall, which is why I'll connect my PIR with wires rather than sit it on the board. It should sit inside a plastic case a bit better that way. I'll see if I can take some photos of my prototypes to show you my thoughts.

[Bandra]

@Zeph
For cutting the boards I'll be using a really sharp Stanley knife. I live in an apartment with my young family, so containing the dust is a big consideration for me. A Stanley knife is about the "cleanest" way to cut them. It just takes a little more elbow grease.

I've left about 3mm between each board (since I have 3 x 3cm boards to fit across 10cm). Plenty of room to cut between :)

Yeah, I know that Nordic recommend not to run the antenna over a plane. I plan to solder a 2x4 header onto my PCB and slot the nRF into that. My prototype had pretty decent range when I tried it. I'll see how it works when my PCBs come in. I may need a rev 2 yet :)

[Zeph]

@therik said:

@Zeph I have a DHT-22 and my pin spacing is 0.1".

Cool.

Oh yea, and where are you getting the DHT22 for $3?

I understand the desire to go below 20% RH.

I am using AM2302. Many of the sources for "DHT22" are actually substituting the AM2302 (including the current MySensors store link). Do you have a datasheet for the real DHT-22?

And I goofed, $3 was based on winning a bid for my first one, they start at $4 w free shipping on eBay for "Buy it Now", tho they can be had for closer to $3 in lots of 5 on AliExpress.

I got mine before coming to this site; I would now tend to suggest following the links in the MySensors store if you are getting it from eBay - who knows how good the "cheapest offering" on eBay or AliExpress is?

[Zeph]

@Bandra said:

For cutting the boards I'll be using a really sharp Stanley knife.

Meaning a box cutter knife? So you probably use a straight edge and score the board with the knife (both sides?) Then just break it on the line? That sounds pretty feasible, other than:

I've left about 3mm between each board (since I have 3 x 3cm boards to fit across 10cm). Plenty of room to cut between :)

Ever since SMT, people have new definitions of "plenty of room" :-)

[Zeph]

My overall thinking is that the breadboard area will allow reasonably simple addition of many types of sensors or actuators, so I am suggesting minimizing the dedicated circuitry and maximizing the breadboard area. However it makes sense to have dedicated space on the PCB for sensors and devices which are likely to be commonly used and especially if they do not fit the 0.1" hole grid. For example, a surface mount LDO regulator for the radio.

There's another candidate which meets this criterion for me, and I've edited it into the Origional Post - onboard external serial Flash. This could be as easy as a SOIC-8 outline (and traces) for the AT24C series, or other serial Flash memory. Optional of course.

[therik]

Gentlemen,

For anyone who is interested I have attached a schematic of my proposed "shield". Have a look if you so choose, and if you notice something wrong or incorrect, please let me know. One thing I'm not sure is...does the DHT22 temperature/humidity sensor need an external pull-up resistor?

[therik]

Oh yea, be nice...it's my first one!

[Zeph]

@therik said:

Very nice. No "mistakes", just some questions.

For anyone who is interested I have attached a schematic of my proposed "shield". Have a look if you so choose, and if you notice something wrong or incorrect, please let me know.

This is a base board for the Arduino Pro Mini, right? Are you making use of A6 and A7?

Why three voltage dividers of this style? Do you anticipate having multiple higher voltages to measure? I would tend to use one for VRAW. I guess you could populate one half with a resistor and jumper the other, then tie something like an LDR between the analog input and VCC or Ground.

I'm a little unusual, as I want the option to tie the nRF's IRQ to D8 (input capture 1). This is to allow T1 to be used as a high precision timer and capture the time a packet arrives, and I can also use that capture to generate an interrupt based on that - keeping D2 free for INT0.

I am also using an interrupt driven DHTxx lib, which uses Int0 or Int1 (pin 2 or 3) rather than pin 5.

Are the PIR and Dallas (one wire) and DHT22 dedicated footprints on the board, or connectors?

[therik]

Indeed, a pro-mini clone. I thought that A6 and A7 might be too much to squeeze in. I'm thinking of a 3x5 cm board.

Yea, for the voltage dividers, one for measuring the battery level. And two for something else, possibly an IR-based reflective optical sensor. And anything that has a higher output voltage.

Hmm...haven't heard of using nRF's IRQ to D8, can you still wake a sleeping node with this configuration? I guess I just don't have a full grasp on the concept. I just a beginner, so the more I learn the more dangerous I get!

Right, the main sensor on this board is the PIR; which is why I want an interrupt pin to that sensor. However I'd like to also use the magnetic-based sensors also as the main sensor and interrupt.

The PIR, Dallas, DHT22 are separate from the other 'future-proof' region, this should become clear once the layout is complete.

Anyone have a solid answer on whether the DHT22 needs an external pull-up resistor?

[Zeph]

@therik said:

Indeed, a pro-mini clone. I thought that A6 and A7 might be too much to squeeze in. I'm thinking of a 3x5 cm board.

OK. I like to use one of them for a dedicated measurement of VRAW, since it cannot be used as an additional digital I/O like A0..A5

Yea, for the voltage dividers, one for measuring the battery level. And two for something else, possibly an IR-based reflective optical sensor. And anything that has a higher output voltage.

What IR based sensor are you considering that returns analog above VCC? Are you thinking of having 5V power supply and sensors with 3.3v APM?

Hmm...haven't heard of using nRF's IRQ to D8, can you still wake a sleeping node with this configuration?

I believe the answer is "yes, but not in the lowest possible power-down mode".

Case 1: The nRF is power up and may generate an interrupt. In that case you are using a significant amount of power; you can save battery by nevertheless mostly powering down at ATMega, but keeping timer 1 active so D8 can generate a Input Capture 1 interrupt won't be a big deal.

Case 2: You want really minimal power - so the nRF is powered down and isn't generating interrrupts. In that case you don't need D2 or D8, and you can go to the lowest power level (including powering off timer 1); the watchdog may be all you leave running (or some other super low power external device).
At least that's my understanding. I'm still learning too.

Anyone have a solid answer on whether the DHT22 needs an external pull-up resistor?

I do not use any pull up resister and I've never seen a circuit which used it.

[Zeph]

@Zeph said:

There's another candidate which meets this criterion for me, and I've edited it into the Origional Post - onboard external serial Flash.

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

Isn't anybody willing to create a SOIC-8 home for this cute little chip (with SPI traces of course to keep it happy)?

512 KBytes of happiness for logging and OTA programming. Unique ID.
Or you can get twice that memory for 2 cents more.

(The above is the chip used by the Moteino. The Anarduino uses a heftier 16 MByte chip: http://www.mouser.com/ProductDetail/Spansion/S25FL127SABMFI101/?qs=sGAEpiMZZMtI%252bQ06EiAoG5SEO4xJJ6RlEmMSz7h3HuQ%3D but that too is possible with the same SOIC-8 footprint, I think)

(The Moteino and Anarduino use different and incompatible radios compared to MySensors, but nevertheless contain possible inspirations for our corner of this exciting little world).

[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 :)