Author Topic: Associating parts for an RFM69HW breakout board  (Read 4383 times)

sketchy

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Associating parts for an RFM69HW breakout board
« on: March 04, 2014, 04:21:09 AM »
I created a new post where I discuss what I have learned about picking parts and associating the parts with schematic symbols.  http://bitknitting.wordpress.com/2014/03/03/associating-parts-to-the-schematic-symbols-for-a-rfm69-breakout-board/  in case you're interested.

uChip

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Re: Associating parts for an RFM69HW breakout board
« Reply #1 on: March 04, 2014, 12:22:19 PM »
Nice work.  Seems you have successfully navigated the Digi-Key UI and filter system.  It takes some getting used to.  Once you know it, you'll find it is a very powerful way of finding that needle in the haystack.

One comment on your choices: Your selection of the 1703 in the SOT-23A case has a more limited power dissipation.  That case has a high thermal resistance which in English that means that the SOT-23 will get hotter for a given load current than some of the other cases.  Probably not a problem if your only application is to wake up once a minute take a reading, send a packet and then go back to sleep.

If you might use your breakout board in some more continuously transmitting application the SOT-23 might not cut it.  Consider the SOT-223 case instead.  It is five times as efficient at heat dissipation.  For detailed descriptions see section 6.2 of the 1703 datasheet.

Good luck,
  - Chip

sketchy

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Re: Associating parts for an RFM69HW breakout board
« Reply #2 on: March 05, 2014, 05:51:52 AM »
Hey Chip,
Thank you for your help.  Your comment:
Nice work.  Seems you have successfully navigated the Digi-Key UI and filter system.  It takes some getting used to.  Once you know it, you'll find it is a very powerful way of finding that needle in the haystack.

One comment on your choices: Your selection of the 1703 in the SOT-23A case has a more limited power dissipation.  That case has a high thermal resistance which in English that means that the SOT-23 will get hotter for a given load current than some of the other cases.  Probably not a problem if your only application is to wake up once a minute take a reading, send a packet and then go back to sleep.

If you might use your breakout board in some more continuously transmitting application the SOT-23 might not cut it.  Consider the SOT-223 case instead.  It is five times as efficient at heat dissipation.  For detailed descriptions see section 6.2 of the 1703 datasheet.

is ABSOLUTELY WONDERFUL. THANK YOU.  A big reason why I tediously write the blog posts is to get feedback on how to increase my knowledge with the goal of understanding aspects in electronics that I don't know to ask and will greatly enhance the hw/sw experience I wish to design and build.  I will be following up understanding power dissipation better.  Your comment gave me insight into this challenge (which seems like an obvious one now :-) ).

Totally appreciate the time you took to help me.

Felix

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Re: Associating parts for an RFM69HW breakout board
« Reply #3 on: March 05, 2014, 07:57:09 AM »
I've not ever seen any heating or smoke out of that regulator in my own practice. Some people reported heating but I suspect they misused it or shorted the outputs (which WILL cause heating).
Wireless programming for instance is very RF intensive for a period of 20-30 seconds or even more depending on the sketch size. And there is no heating. So it's a bit of a myth that the SOT23A is a bad choice. If it were, I would have replaced it over the several revisions of Moteino.

sketchy

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Re: Associating parts for an RFM69HW breakout board
« Reply #4 on: March 05, 2014, 08:40:00 AM »
Hey Felix,
Excellent point on usage scenario when it comes to power dissipation requirements.  My scenario has receiving a small amount of sensor data from many nodes.  Thus, the RF is used - as you point out - in bursts and i dont need the data that often - probably at most 4 times a day, unless there is an alert (e.g.: the air temperature on a sensor node is too high for a particular plant).  I find heat dissipation with regards to PCB layout and chip selection to be a bit complicated for me to grok at this time.  Hopefully, in the future this will all make sense (and I will have folks like you and Chip to thank).

kobuki

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Re: Associating parts for an RFM69HW breakout board
« Reply #5 on: March 06, 2014, 01:41:02 PM »
Sorry if it might not fit the topic perfectly, but seeing that you talked about the selection of Microchip LDOs too, and I'll need to choose one of the available models for a future project, I'd like to have a question: out of the 1700, 1702 and 1703, which has the lowest dropout voltage in practice? It is supposed to be the 1700, so I tend to lean towards it. How stable is it near the low end of the difference foltage at Vin (any model you have experience with), and what load can it handle? I mean, in practice (I've already read the datasheets).