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legailutin

Yet Another Wireless Sensor Board

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Hi,

I've finally found my "cahones" and decided to become a doer, and hopefully more active on the forum.

I've been working on his for more than a year on my free time and have learned a lot. However, nothing real have come out of this project until recently. With the recent release of energia library for nRF24L01P by spirillis, I decided to restart working on it. Anyway. I'll post what I've done so far and move along with the suggestions.

 

I'm a noob, so I've gone the noob way:

  •   Breadboarded first using what I had in my noob bin (msp430g2553 , nRF24l01P, ds18b20, thermistor, 7805, lm358, 9v battery, couple of resistors and capacitors)
  •   Used the launchpad schematics to get the components values.
  •   Board Layout with fritzing. Eagle was too complicated for me.
  •   Ordered the board thru Oshpark after exporting the gerbers. [ yay!!! I'm speaking like the pros :grin:)
  •   Programming with Energia, so far everything is going ok.

I attached the fritzing file as well as the oshpark rendering of the board. Please, take a look, let me know where I've gone wrong.

YAWSB.zip

post-228-0-58127700-1360557311_thumb.png

post-228-0-57646000-1360557346_thumb.png

post-228-0-47912300-1360557371_thumb.png

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Looking good, some remarks:

 

the IRQ line is really close to the circular pad of the 470 ohm resistor, I'm afraid they might short eachother.

try to avoid 90 gegrees angles (lice the GND, VCC and CSN lines of the nRF) as they are more prone to peel off of the board than weaker angles.

 

7805 are very power unfriendly, are you going to battery power? If using AA cells, why not tap off of 3 NiMH or 2 Alakine cells for the 3.6 and use 3 Alkaline or 4 NiMH cells for the 5V? If you must go with a power regulator, try to use DC-DC or switching designs, linear regulators like the 78xx series basically "burn" the volts over the required voltage. (More correctly, the current draw will be equal, no matter the input voltage; hence the power usage increases with the input voltage)

 

Further looks quite nice!

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The IRQ line is really close to the circular pad of the 470 ohm resistor, I'm afraid they might short eachother.

try to avoid 90 gegrees angles (lice the GND, VCC and CSN lines of the nRF) as they are more prone to peel off of the board than weaker angles.

There are quite a few areas that I think will short. OSHPark expects 0.15mm trace clearance. I usually design for 0.20mm trace & 0.20mm clearance with OSHPark, though.

 

I agree that Eagle has a terrible UI. DipTrace has a much nicer UI, you should try it. There is a free, hobbyist version that would meet the requirements of this board. Its schematics are a bit uglier and I'm told the autoroute in Eagle is better, but I never use autoroute anyway -- I design only relatively simple mixed-signal and RF boards.

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Thanks already for the feedback.

 

the IRQ line is really close to the circular pad of the 470 ohm resistor, I'm afraid they might short eachother. try to avoid 90 gegrees angles (lice the GND, VCC and CSN lines of the nRF) as they are more prone to peel off of the board than weaker angles.

 

 

Thanks rr, I can miraculously see all the short 8-) on my board now. lol. I'll also change the angles on the traces. When I ran the design rule check with it's "professional" autorouter setting, everything showed ok in fritzing.

 

There are quite a few areas that I think will short. OSHPark expects 0.15mm trace clearance.

 

In addition, I looked everywhere to see where I can add clearances to the design rules. I guess I just hit the first roadblock. Thanks for pointing at diptrace. Never heard of it before but determined to try it out. One question though, how to understand the 300 pins limit metric? Is a hole equal to one pin? or is a pad considered a pin?

 

 

7805 are very power unfriendly, are you going to battery power? If using AA cells, why not tap off of 3 NiMH or 2 Alakine cells for the 3.6 and use 3 Alkaline or 4 NiMH cells for the 5V? If you must go with a power regulator, try to use DC-DC or switching designs, linear regulators like the 78xx series basically "burn" the volts over the required voltage

 

For the power, I didn't want to order new parts. In this iteration, I just decided with things I could easily find in my bin and that most noob will  also :)

 

The thing was looking forward to doing was to learn how to use a ldo for 3.3v but your suggestion of skipping all that with 3 alkalines sounds a lot better to me as it involves less parts on the board.

 

Now, I'll like to share with you couple of facts and get your impressions.

I prototyped my wireless sensor stations using 2 launchpads + spirillis boosterpack + nrf24l01P + ds18b20. The radio modules are the cheap ones from ebay (8pins + trace antenna).

  • The radio modules have a very poor range. One of the stations was setup outside, under my patio and have been running for the last week. I had to setup the receiving station not even 5 meters from the sensor to pick-up the signal. Is there any way to improve the signal quality? 
  • Everytime the temperature gets close to 4 degree C, the station basically "freezes." I mean, nothing is transmitted. Could this be that the ICs do not support low temps? 
  • For now, I'm running the station off powered usb. I'll eventually have to move to batteries and implement low power modes. Is there a way to programatically check how much battery has been used ? I mean, I'd like to implement a low battery alert using the led.

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Thanks for pointing at diptrace. Never heard of it before but determined to try it out. One question though, how to understand the 300 pins limit metric? Is a hole equal to one pin? or is a pad considered a pin?

 

The free, non-commercial license is up to 500 pins, 2-layer.  A pin is any pad or pin.  500 pins is more than you'll need.

http://www.diptrace.com/nonprofit.php

 

 

 

 

Now, I'll like to share with you couple of facts and get your impressions.

I prototyped my wireless sensor stations using 2 launchpads + spirillis boosterpack + nrf24l01P + ds18b20. The radio modules are the cheap ones from ebay (8pins + trace antenna).

  • The radio modules have a very poor range. One of the stations was setup outside, under my patio and have been running for the last week. I had to setup the receiving station not even 5 meters from the sensor to pick-up the signal. Is there any way to improve the signal quality? 
  • Everytime the temperature gets close to 4 degree C, the station basically "freezes." I mean, nothing is transmitted. Could this be that the ICs do not support low temps? 
  • For now, I'm running the station off powered usb. I'll eventually have to move to batteries and implement low power modes. Is there a way to programatically check how much battery has been used ? I mean, I'd like to implement a low battery alert using the led.

The Nordic parts have never been known for having long range, but you many have chinese knock-offs or simply units that didn't pass testing.  I suspect that is the case.  If I had to guess, I would say this chip has a grounding problem.  With the low-temperature freeze, it might also be your battery, but I suspect it's just that you have a bad PCB or bad chip.

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I went with channel 83 and 1Mbps rate. I'll try the 250kbps sometimes later.

 

 

but you many have chinese knock-offs or simply units that didn't pass testing.

 

 

I do have the cheap chinese boards. :) I wouldn't have felt comfortable investing 20 bucks for one unit with sma antenna. mainly doing this for the fun and learning.

 

Even wifey is getting jealous of my new best friends called DS1052E and Saleae Logic. Hope I'll never have to choose.

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What bitrate for the nRF24?  I find 250Kbps is needed for anything decently far... although you lose the auto-ack/auto-retransmit feature at that speed.

That totally depends on your needs. You could always do retransmission in software. A lot of applications can do with 9600bps, so where do you need 250k for?

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The Nordic nRF24 modules do full-service protocol handling, so you're at the mercy of their bitrate options, which include 250Kbps / 1Mbps / 2Mbps. So 250Kbps is the slowest/best range option for those $1.20 modules :D

 

Sent from my Android tablet using Tapatalk

 

 

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I went with channel 83 and 1Mbps rate. I'll try the 250kbps sometimes later.

 

but you many have chinese knock-offs or simply units that didn't pass testing. 

 

I do have the cheap chinese boards. :) I wouldn't have felt comfortable investing 20 bucks for one unit with sma antenna. mainly doing this for the fun and learning.

 

Even wifey is getting jealous of my new best friends called DS1052E and Saleae Logic. Hope I'll never have to choose.

For what it's worth, when I set up my grill monitor project I wrote a routine to scan the channels for activity and I noticed the middle channels were the noisiest (probably WiFi) and channels below 20 and above 110 were quietest. My setup uses channel 10.

 

Sent from my C3PO via Tapatalk

 

 

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For what it's worth, when I set up my grill monitor project I wrote a routine to scan the channels for activity and I noticed the middle channels were the noisiest (probably WiFi) and channels below 20 and above 110 were quietest. My setup uses channel 10. Sent from my C3PO via Tapatalk

That sounds like a useful bit of could - share?

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That sounds like a useful bit of could - share?

Check out the Enrf24 lib on github for Energia -- It's in there as one of the examples!

https://github.com/spirilis/Enrf24

 

https://github.com/spirilis/Enrf24/blob/master/examples/Enrf24_ChannelScan/Enrf24_ChannelScan.ino

 

 

(and make sure your Energia install has this patch so Serial doesn't clobber SPI -- http://forum.43oh.com/topic/3272-msp430g2553-issue-hardwareserial-io-corrupts-spi-io/ )

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That totally depends on your needs. You could always do retransmission in software. A lot of applications can do with 9600bps, so where do you need 250k for?

 

If you don't need much range, higher data rate means less time spent in transmit, and hence less energy used on a beacon.

 

I took a look at the NRF2401+ datasheet.  Indeed, it uses a self-interfering modulation scheme for 1Mbps and 2Mbps, so range is going to be really poor on 1Mbps and 2Mbps.  Bluetooth uses a similar scheme.

 

Even so, you may have a grounding issue or just a lousy antenna.

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