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Rfm69 esp8266 arduino11/7/2023 ![]() I have compromised and have cut my antenna wires to 80mm total (including the section going through the PCB). There are however other factors which could cause similar effects deeming it wise to use lesser than exactly ¼ wave-length. As for 915Mhz that would be less than a foot and normally you operate this unit much higher from the ground than that, I dismiss this 78mm length. ![]() I understand that antenna tech says when the antenna is within a ½ wave length of earth ground your antenna will act like it is ~5% longer than it is. For those that are interested this gives a little more information on how I got there.Ī ¼ wave length for 915MHz is 82mm. įor your implementation of these units you can skip this section. To make all the measurements easy and accurate, I really like this inexpensive caliper. Alternately a piece of scotch tape over the hole for audio is effective. This device does not make a lot of noise, but if you are concerned about attracting the attention of others, then it provides the option of using an ear phone. I would not use green as that color is otherwise used for signaling information. A green or maybe a blue LED could be used but not yellow or red as their voltage drop is too low and would make it look like the button is pressed. With such little drive this LED must be a high efficient one. It was simple to add as I wired it across Btn1 which is given some drive current from an internal resister (~37k). Also a portable speaker amp could be connected to it. Misc: soldering supplies, tape, hot glue, prototyping tools.Ī stereo jack to connect an ear piece, to be sure not to miss incoming communications. 2 each resisters … 270 Olm, 1.5kOlm, ~5k Ģ6ga wire solid or 24ga stranded, for grounds and +V ![]() 4 Red-Green 5mm Common Cathode Bi-Color LEDs (wiring & breakdown voltage is important) 2 Li-ion 3.7v 200+mah batteries (7x20x30mm, ~Maximum size usable 9x24x36mm) 2 Case (was to be a battery compartment) Also note that I use the 'H' high power version of the radio modules. They could also be used as pagers with 3 levels of attention requests, when someone is convalescing or working under the house.īeyond that they can be a lot of fun, especially for kids or students.Īs the radio module can not handle a 5v supply or signal voltage, you must use 3.3v MCUs. The units do not support any voice (analog) communication. The units support a set of, digital, 10-20 (location?) style question and answer codes (refer to wiki/Ten-code ) as well as optional Morse code. But they cost much more, which for me was unwarranted. There are a few LoRa devices (like a RFM95) out there that are of similar size and interface. The RFM69 radio modules are much more efficient and effective over greater distances then either a NRF24L01 or an RFM12.įor even greater reliable longer distant connections this project could be made to used LoRa radio modules just as well. They can communicate over 100 meters using low power, on only 10s of milliamps, and as much as 1/2 kilometer or even 1/2 mile using about 120 ma. They are very efficient, low power, radios using digital packet communications. These “2-bit” (digital) radio communicators provide a means to signal each other (as to where they are if their done …) when shopping at opposite ends of a big box store even where cell phones have no service or cell battery charge.
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