I want to be able to control a device, say a switch, using Bluetooth BLE. Should be Switch be a Bluetooth server or client and why? I expect to use a ESP32 for both the server and client but only one will be controlling a switch.
In the Bluetooth LE world the word server and client feel a bit out of place with our normal world concept of a server. The server in BLE is usually the simple device (e.g. light bulb) that waits for commands from clients which often are more complex e.g. smart phones.
A switch (e.g. push button) does not wait for commands it sends commands so it should be a client. Whatever receives the command and reacts to it, is the server.
If with switch you mean a relay that switches something on or off than the term is wrong. A relay would be a server.
I hear you but what about low power. I have some WYZE contact sensors. In order to keep the power low, I would think that they would be a client, basically just doing nothing until the contact changed and then it would send a signal to the server, i.e. a bridge I think. Now if I have a light bulb, like the C by GE that are controlled via bluetooth by a google mini, then I guess this would run a server. Power would not be an issue as the power can come from the 110 volt main.
Now, if I had a battery powered water sprinkler controller I would think that would have to be a server since my cell phone or other controller would have to send commands to it. This means the server would always have to be ON, i.e. waiting for a signal. So I guess the power consumption would depend on how low power the Bluetooth server is. However, the battery powered sprinkler valve could be a client that periodically connects to a server to see if it should be on or off.
I should point out that I do not know if the WYZE sensors use Bluetooth or not. They might be 433 MHz devices.
Do you know how the "Tiles" work? They are the things that you attach to your keys so if you lose them you can find them with a cell phone app. These work for about a year on their batteries. I am assuming these are Bluetooth Clients that continually ping the users cell phone at some low rate. Once the Tile gets so far from the cell phone that the signal is lost, the cell remembers the last location.
I have not seen much documentation as to how these things work. I am curious.
barryjo:
This means the server would always have to be ON, i.e. waiting for a signal. So I guess the power consumption would depend on how low power the Bluetooth server is. However, the battery powered sprinkler valve could be a client that periodically connects to a server to see if it should be on or off.
In Bluetooth LE the server is lower power than a client, because the server advertises with 3 very short messages (3 advertisement channels) and then immediately looks for an answer and then shuts off for an interval. The client needs to be on for a much longer time to catch the advertisements.
Do you know how the "Tiles" work?
From what I have seen on Amazon about the Tiles, I am certain they only send out advertisement packets (they are servers). They do not need to do anything else (BLE allows non connectable ads). The smartphone needs to scan for the UUID and because it knows how strong the transmitted signal is, it can even figure out how far the tile is away. They seem to be quite expensive for the functionality they have. You can try something like this with one of the new Arduino Nano 33 IOT or BLE and an App like BLE scanner. The app will show you the RSSI.