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Feather accelerometer, RF transmitter, data logging project.
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Feather accelerometer, RF transmitter, data logging project.

by wahleworld on Sun Nov 11, 2018 1:24 am

Hello:

Before I get into the details of my project I wanted to share my level of knowledge surrounding coding and electronics. I don't know much. But I'm excited to learn more, and am open to any and all suggestions, or constructive feedback.

After several weeks of research I've narrowed down the components to what I think would be the easiest to work with, and learn on.

WHAT I NEED:
1. Acceleration detection.
2. RF transmission to another device <750ft away.
3. data logging
4. Preferably using AA or AAA batteries
5. Decent battery life
6. Visual low-battery notification?
7. Small

My plan was to use the 32u4 Adalogger, with a featherwing proto on top of that with a RF transmitter and accelerometer. An issue I'm experiencing is the lack of an accelerometer specifically designed for the feather. Can I use another adafruit accelerometer (LIS3DH, MMA8451) on the proto? I had also anticipated using a breakout board (RFM69HCW) for the RF, attached to the proto? Or I could use the RF feather as a second layer to the data logger? Is it reasonable to power a device with all three components via AA/AAA? Do I need the MO data logger due to project requirements or anything? I had thought I could attach the AA/AAA battery bank to the battery connector, but it sounds like that is not true?

I plan on having a friend help with coding and have been watching tutorials. I've taken a entry-level python class so I understand the basics.

Feel free to offer insight on any/all of the topics as I'm currently trying to get a feel for how to design the project.

Thank you!

wahleworld
 
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Re: Feather accelerometer, RF transmitter, data logging proj

by adafruit_support_bill on Sun Nov 11, 2018 7:16 am

There are a few workable configurations. I'd probably go with the 32U4-RFM96 Feather, an Adalogger Wing and a Proto Wing.

https://www.adafruit.com/product/3079
https://www.adafruit.com/product/2922
https://www.adafruit.com/product/2884

You should be able to interface any of the accelerometers or IMUs via the proto wing.

The Feathers are desgined to be powered via LiPo and/or USB. It is possible to power using a 3xAAA pack (4.5v) via the USB port. But do not plug anything but a LiPo into the battery jack - since the charge controller is designed for LiPo cells only.

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Re: Feather accelerometer, RF transmitter, data logging proj

by wahleworld on Sun Nov 11, 2018 6:06 pm

Thanks, Bill.

Is there anyway to turn off the charging capability of the Li-Po port? I'd have to alter the battery pack for USB compatibility I believe, and would love to use the adafruit battery pack with Li-Po connection.

wahleworld
 
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Re: Feather accelerometer, RF transmitter, data logging proj

by adafruit_support_bill on Sun Nov 11, 2018 7:25 pm

Is there anyway to turn off the charging capability of the Li-Po port?

You would have to cut some traces on the board to disable the charger.
I'd have to alter the battery pack for USB compatibility I believe,

You could either splice on a USB connector and use the jack. Or connect directly to the USB and GND pins on the Feather.

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Re: Feather accelerometer, RF transmitter, data logging proj

by wahleworld on Sun Nov 11, 2018 7:47 pm

Bill, you're the man!

I'm going to order a few things to play around with, and when I get ready to actually solder some things together I'll get back in touch.

Thank you!

wahleworld
 
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Re: Feather accelerometer, RF transmitter, data logging proj

by wahleworld on Wed Nov 14, 2018 10:00 pm

Can I integrate a visual low-battery notification easily?

wahleworld
 
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Re: Feather accelerometer, RF transmitter, data logging proj

by adafruit_support_bill on Thu Nov 15, 2018 6:54 am

You can measure the battery voltage and turn on a LED when it gets below some threshold.
https://learn.adafruit.com/adafruit-fea ... attery-5-8

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Re: Feather accelerometer, RF transmitter, data logging proj

by wahleworld on Sun Nov 25, 2018 9:55 pm

Hello again:

Just trying to understand the integrated battery connection a bit better.

It is my understanding that I can use the AA/AAA battery packs , with the JST connector plugged into the connector on the feather boards. I also understand that I must unplug the battery pack, before plugging in the USB (or risk something happening to the board/ batteries?) What would happen?

Thank you Adafruit Bill for the info on battery level monitoring. Am I also able to monitor the battery voltage if it were plugged into the JST connector? Or do I need to be wired into the board itself?

wahleworld
 
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Re: Feather accelerometer, RF transmitter, data logging proj

by adafruit_support_bill on Mon Nov 26, 2018 6:49 am

The Feather boards were designed primarily for use with LiPo batteries and/or USB. There is a built-in LiPo charger circuit connected to the JST that is activated when plugged into USB.

You can use other power sources (such as AA/AAA battery packs) in the 3.3v-5v range. But if they are not compatible with the LiPo charger damage to the battery or charger may result.

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Re: Feather accelerometer, RF transmitter, data logging proj

by wahleworld on Thu Nov 29, 2018 2:59 am

Would it be possible to store very small amounts of accelerometer data using FRAM?

The application does not require scheduled reading/write, and will most likely only be recording data from 1 "impact" to the sensor, before it will be reviewed.

wahleworld
 
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Re: Feather accelerometer, RF transmitter, data logging proj

by adafruit_support_bill on Thu Nov 29, 2018 6:47 am

Yes, you should be able to buffer it to FRAM.

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Re: Feather accelerometer, RF transmitter, data logging proj

by wahleworld on Thu Nov 29, 2018 1:02 pm

I had planned on using a microSD adalogger. But I believe I can use the radiowing(RFM69HCW) , with a prototboard on top of the radiowing, with an accelerometer, and FRAM storage. Does this seem like it would be appropriate for detecting an impact, logging the data(only a few readings from accelerometer), and sending a signal to another transceiver?

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Re: Feather accelerometer, RF transmitter, data logging proj

by adafruit_support_bill on Thu Nov 29, 2018 1:29 pm

Does this seem like it would be appropriate for detecting an impact

Are you trying to just detect an impact, or actually measure the peak accelerations at impact? If the latter, my main concern would be about capturing the impact with sufficient time resolution. Depending on mass and physical properties the objects involved, the peak accelerations during impact may be quite short and you would need a very fast sample rate to capture them.

Although FRAM is pretty fast, you still have the overhead of the i2c interface when writing to it. You may be better off going with something like one of the M0 or M4 based Feathers. These have 32K of RAM. So you could avoid some of the communication overhead and log the data directly to the processor memory.
https://www.adafruit.com/product/3177

The other potential bottleneck is the interface to the accelerometer. Most are i2c. But we have some analog versions as well which should allow faster sample-rates. I've used the ADXL377 for drop-test datalogging of medical instruments with good results.
https://www.adafruit.com/product/1413

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Re: Feather accelerometer, RF transmitter, data logging proj

by wahleworld on Thu Nov 29, 2018 1:52 pm

I've been given a task to detect impact, log data, and send an RF signal.

I am also concerned with the timing of the impact and the processing capability of the feather boards, in respect to logging the data in what could be an impact time of less than 0.5 seconds most likely.

The guidelines are rather blurry, and I'm currently analyzing various ways to implement the design. I don't know much about the intricate workings of boards, yet. But I'm learning.

Someone on the project suggested battery life should be over 500 hours for the sensor.. I don't think it's feasible, but I don't know much about low-power consumption devices. I initially selected the 32u4 because I thought it would require less processing power, and therefore draw less current. haha, this is all new material for me, but I learn quickly, and am willing to spend time researching various resources.

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Re: Feather accelerometer, RF transmitter, data logging proj

by adafruit_support_bill on Thu Nov 29, 2018 2:13 pm

I initially suggested the 32U4 because it is a simple and easy to use processor. Although the M0 is more complex and powerful, one of its features is more sophisticated power management. It can be configured to use substantially less power than the 32U4.

To capture 0.5 seconds of raw 3-axis accelerometer data with a resolution of 1ms would take 500ms * 3axis * 2 bytes per channel = 3K of memory. That should be well within the capabilities of the M0.

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Please be positive and constructive with your questions and comments.