RFM69 Auto Transmission Control (ATC)

[papa]

    RFM69 Auto Transmission Control (ATC), Introduction

papa: Though RFM69 Auto Transmission Control (ATC) has long been available, I did not feel the need for it, but recently decided to try it & offer it in our programming.

        Adapted from lowpowerlab.com (including here):

An RFM69 radio's always transmitting at maximum power is usually not necessary. Reducing transmit power even a little saves much battery power.

An RSSI (Radio Signal Strength, shown in negative numbers) is stronger the closer it gets to zero. In the nodes sketch, ATC_RSSI (target RSSI, a negative integer), should be set from very strong (-30) to very weak (-95). Usually set ATC_RSSI closer to the noise floor (-100) since you want to reduce transmit power to the bare minimum.

To save battery on a node, ATC dials down transmit power (-100db is the noise floor, -90db is still pretty good) toward the target RSSI (ATC_RSSI in choose_nodes.ino). For indoor nodes that are pretty static & at pretty stable temperatures, -90db is quite safe. For more variable nodes that can expect to move or experience larger temperature drifts, a stronger setting of ATC_RSSI like -70 to -80 would probably be better. (papa: the sketch has a safe default value of -80.)

To ensure ATC will perform expected, always test your ATC node in the edge cases of your own environment. When ATC is activated in both Gateway & node sketches, this setting enables the gateway to work with remote nodes to dial down their power to the required level.

See here for more lowpowerlab.com discussion of ATC.

    Next, Automatic Transmission Control, Implementing

[papa]

        Automatic Transmission Control (ATC)
            Implementing on Gateway AND Nodes

Automatic Transmission Control requires the RFM69_ATC.h library to be installed in your Arduino IDE. You may already have that library if you installed a recent master RFM69 library from here.

Needed in order for the following to work: See this thread on achieving an RFM69 Gateway & RFM69 nodes.

        Once you have built Gateway & node devices ...

Starting with this post, download the latest RFM69 Gateway sketch. Be sure you do the usual customizing in this post. In the latest Gateway sketch, UNcomment #define ENABLE_ATC. You may now upload the Gateway sketch to its device.

From here, download the latest choose_nodes sketch & follow the basic customization in that thread. Also in the latest choose_nodes sketch, by UNcommenting the needed #define lines, activate the other features of your node (sensors, etc). In the latest choose_nodes sketch, UNcomment #define ENABLE_ATC. You may now upload the choose_nodes sketch to its device.

        Next, Automatic Transmission Control (ATC), Comments

[papa]

        Automatic Transmission Control (ATC),

             Comments & Testing Results

I adapted the choose_nodes ATC code from the lowpowerlab.com Gateway sketch & node sketch. They are included as examples with the recent RFM69 master library.

Previous to adding ATC, the Gateway sketch has filled much of the Arduino compatible's memory. However, the sketch with ATC activated still fit.

Reminders: For ANY node to use ATC, both it & the gateway must have ATC enabled. However, a non-ATC node will still communicate (other than ATC) with an ATC-enabled Gateway.

Thoughts on when to use ATC: To save a battery on a node. On
wall-powered nodes, to reduce radio signals in one's location. Maybe
when to not use ATC: A distant from the gateway node (even on battery)
with obstacles between it & Gateway. Watch the node's device 9 to
see if it needs several attempts to get its message to the Gateway.

        Automatic Transmission Control (ATC), Testing Results

To test results, I watched the ATC Gateway Serial Monitor while an ATC node was running: The Gateway & node both have a coiled antenna (more compact, but less effective than straight). Both the Gateway & node had activated #define ENABLE_ATC. The node used the default #define ATC_RSSI -80. The node was about 30 feet from Gateway with no obstacles between them. Transmit attempts (device 9) were always 1. RSSI started at -55 then the signal got stronger at -49, -50. Then the signal got weaker at -55, -58, -61 .. -64, -62, -61, -65, -60. After a while, it settled (plus or minus) to around -60.