Totally new to mqtt. I understand what it can do but how can I find out which devices that can be used if I want to send sensor info over mqtt
I’m not exactly sure this was your question, but the HA components that use MQTT are listed here
This did not help. What I dont understand is how to find out which devices that can be used. If I read in the list you suggest I get even more confused
Under cameras
The mqtt camera platform allows you to integrate the content of an image file sent through MQTT into Home Assistant as a camera. Every time a message under the topic in the configuration is received, the image displayed in Home Assistant will also be updated.
This can be used with an application or a service capable of sending images through MQTT, for example Zanzito.:
It does not say anything about which devices that can be used
When a device can be integrated in HA you can use MQTT.
I have also looked into this for a while but it’s not clear what devices can be used with MQTT. I have quite a few existing devices but I have no way of knowing if they can be used with MQTT. Confusing.
As one might perhaps expect, there is no list of devices that can use mqtt, any more than there is a list of devices that can use http. You may get more useful help if you asked about the capabilities of a specific device that you are interested in using with it, and see if anyone has written suitable software to interface it with mqtt if it does not have native support. (And this may not be the right forum to ask that question! 
)
For my part, I use mqtt and HA with
- Sonoff sockets/switches/sensors, using the Tasmota firmware
- Broadlink RM, using mqtt_broadlink
- C-Bus structured lighting, using cgateweb
- Amazon Dash Buttons, using mqtt_dasher
Unfortunately all guides on Mqtt say it is the solution for so much but not a word anywhere that it can only be used if there is a special firmware that can handle mqtt
I guess most manufacturers right now see their best business models as buy-our-proprietary-hub-and-pay-a-subscription or use-our-cloud-so-we-can-sell-your-data. Putting in open protocols (like public, native mqtt functionality) rather undermines those models, hence the lack of devices with native support.
There is sooo much other devices that does not need this model. Like ip cameras. Thats why I am interested. I use the Xeoma surveillance platform for my cameras. I get a much more competent motion detector and much other features than any PIR or those built in to cameras. The platform can be used to send mqtt by using http requests but it is a very complicated and not very skilled way to do it. I have asked the developers to develop a module for mqtt and hope they will do that. But there is ofc 1000 other very useful devices out there that has no interest of developing own hubs and protocols. I think it is just a matter of reaching out to them
Good luck with the reaching out. It sounds like you have answered your own question
I have reached out to only one because I know them