I agree. I had lithium ion pouch cells in a remote sensing application and made the mistake of placing the unit at about 100 mm above ground. On a hot sunny day ground temperature reached above 70 C and the cells vented. Stank. My next deployments will place the unit at a minimum of 1000 mm above ground, or buried at least 30cm below ground, or supplied with a passive airflow derived from an underground pipe. Or enclosed in a big thermal mass that uses the night cooling to average out the day heating.
That’s a good thing to test. it should be relatively shaded most of the time, but most of the time isn’t all of the time. I’ll have to wait for it to warm up some and get sunny again.
In the meantime, I guess it’s back to looking for LEDs and maybe a better enclosure. Although I’m not confident that one exists that suits my needs.
That looks like a good enclosure. Figure out a way to put vents both bottom and top so that hot air can escape and cool air can replace it, without allowing water ingress.
No, no, I can’t do that. That’s too smart. hahahaha. Thanks for the idea! Finding another breather vent for the top is likely way easier than finding another enclosure.
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Hello Everyone!
I’ve gotten the designs of my three next boards to a point I’m comfortable talking about them!
The boards:
- Hand-held Transmitter
- Battery Powered Receiver Light
- Battery Powered Dimmable Light
I’ve built some prototypes based on the Feather 32u4 RFM69 (915MHz version) and they are working well for the most part. I need to fix up some programming bugs and track down a potential hardware failure that I caused. But I’m comfortable with moving forward to custom PCBs. As a side note, I’m only building a few of these each (5 in the first run) but I’m trying to keep some ideas of manufacturability in mind.
My questions:
- With a target range of 100-200 meters through moderate forest, does this unit have enough transmit/receive power/sensitivity with this spring antenna link
- Is the RF layout good at all? Or am I missing something
- Has anyone used a MIC1557 timer
- Besides a uCurrent or Joulescope, do I have any way/hope of measuring sleep/idle currents?
Range Calculations:
I have done some thinking/used a few link loss calculators and from my guesses about certain things, I seem to have more than enough power to reach 200m. The RFM69 has a max transmit power to +20dBm, a receive sensitivity of at least -100dBm, and the antenna has a gain of +2.15dBi with a Vswr of ~1.5.
RF PCB Design:
I tried implementing what I know about RF design, which isn’t a ton, but this is where I got to. I tried to keep the track from the RFM69 to the antenna connection point as short as possible. I also used the KiCAD PCB calculator to try to match the track’s impedance as close to 50 Ohms as possible (ended around 51-52 Ohms, which I am comfortable with).
I removed the copper ground planes from underneath most of the antenna, although I’m not sure if that is what I should do. I’m also not sure if I need to add via stitching around both the trace going to the antenna and the ground exclusion zone.
As a side note, the antenna I would like to use is the spring antenna, but I’m keeping a u.FL connector available just in case I do need to use a different antenna. In that case, I’m not entirely sure which one I would use or where I would end up mounting it, but one problem at a time.
In both photos, U401 is the RFM69 module.
MIC1557 Timer:
The MIC1557 seems like a nice timer chip, I want to use it to create an adjustable PWM signal via a potentiometer. So far, I’ve set it up like below, which is based on the datasheet and the similar circuit when using a 555. I could just use an ATtiny with a small amount of code, but I like the idea of doing it in simple hardware only. And I can’t use an NE555 due to the temp range that I would like to hit (ideally -40 to +85 C).
I’m open to doing it with another PWM chip if anyone knows of anything that is similar, and is in stock.
Also curious on thoughts around if I’m over-complicating this one at all. I’m starting to think I might have.
Thanks in advanced, this was a long one. 