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Hello, I am designing a pcb that uses an Arduino nano and a LORA module to blink a light and communicate with other lights that have the same hardware.
I have two things I need help with:
I was planning to use the RFM95W LORA module but didn’t realize that it doesn’t have a built in antenna. Is there a small Antenna that can be soldered onto our PCB and communicate over short distances (at least like 50 meters). Or are there other LORA modules with built in antennas that can replace the RFM95W in my design to complete the task?
We plan to have 2 SMD LED’s on each PCB connected to digital pins of the Arduino Nano 33 BLE sense. We need LED’s that are between 12-35 Candelas and the Arduino digital pins can support them voltage and current wise. Our board is designed to fit LED’s of package size 0805 right now but we can change that if there is an LED that meets our criteria in a package size that is similar. Do you guys have any LED’s that will fit this description?
Hello RFM85W,
Thank you for contacting DigiKey Technical Support and welcome to our community.
I am sorry to inform you that I could not find a cross with antenna for PN RFM95W. These are the 0805 LEDs we have available
1000 Millicandela Rating = 1 candle
I am sorry to inform you we do not carry a single LED that high of light.
As for the LEDs, we indeed don’t carry any 0805s that are that bright. You’ll likely have to change the footprint on your circuit board. Here is a list of our 12-35 Candela LEDs that can be driven from an Arduino output pin, (assuming you pair them with an appropriately sized resistor, of course). There are a couple of 1208s in there that may suit you…
Edit:
My bad. I was looking at the Nano and not the Nano 33 BLE.
Did you mean to say 12-35mcd (millicandelas) or candelas? In the 0805 size, that’s a very ambitious target to meet.
Also, viewing angle plays a big part in that number, as very narrow viewing angle LEDs will have a much greater candela rating for a given package size, since a given amount of light is concentrated over a narrower beam angle.
Also, reading a bit on the Arduino Nano 33 BLE, it looks like they are specified for a maximum of 15mA per I/O pin and at that current, the the max voltage they could pull down would likely be a bit less than 3.3V.
Thank you guys for the information! With regards to the light, I am okay going with a larger package size as long as it stays relatively small. What is the brightest light that I can run with the Nano 33 BLE sense and is still a reasonably small package size. The light is intended to sit inside a construction zone light casing and flash. So anything that will be easily visible.
With the LORA would you guys recommend I add a terminal to my PCB connected to the antenna pin of the RFM95W and try to find an antenna to use or is there another small surface mounted LORA module that has a built in antenna and would be easier? Thanks!
Have you considered adding some simple switching circuitry to your design to increase it’s driving capability? An N-channel MOSFET is often used for such a task (along with a couple resistors to ensure proper operation). Doing so would afford far more flexibility when it comes to selecting an LED for your application.
Not sure what you mean by “terminal” here… If you mean a footprint for an antenna connector, then sure, why not? If I was in your shoes, I’d probably duplicate what Adafruit did on their breakout board:
This way, you can try a simple whip antenna like I mentioned before and test it’s performance. If it doesn’t cut the mustard, you could then replace it with an SMT uFL connector or an SMA edge-mount connector and try a higher-quality antenna.
If you mean a module with a chip antenna or a PCB trace antenna like those shown below, then you’re probably not going to find much luck there. These antennas are less common on sub-ghz modules. This is especially true for LoRa modules as most applications prefer to take advantage of their long-range capabilities.
Agreeing with @Matt_Mielke about both the RF modules and driving the LED’s with a MOSFET. With a MOSFET, you can essentially use as much current as you can afford to pull from your power source by going that way.
First, it would help if you could define your maximum footprint/height requirements for the LED. That would give a boundary from which to select options.
Second, “The brightest light” is somewhat subjective because of the viewing angle issue I mentioned previously. If you use an LED viewable from a broad range of angles, it will not appear nearly as bright as a comparable LED with a much narrower viewing angle. So it depends significantly on whether you need a wide viewing angle or not. Perhaps you could compensate somewhat by using more than one LED arranged such that they are directed at different angles to cover the field of view you require.
Third, what are the ambient light conditions expected? Is this an outdoor or indoor construction zone? Outdoor will require far more light than indoor.
Fourth, what type of power supply do you have, and, if battery powered, how long does it need to last on a charge or set of batteries? That would dictate the amount of current available for the LED(s).
Fifth, you also haven’t mentioned which color you want or need. Note that different colors have different voltage requirements, with white, blue, and some greens requiring more than 3V to reach full brightness. If you have a power supply available with greater than the 3.3V required for your Nano 33 BLE, then by using a MOSFET between your I/O pin and the LED, you have much greater flexibility in your LED options.
