[werk_ag]

I have finally finished my 4Pro transmitter unit.
Can the UVM-30A and the solar cell for solar radiation measurement be connected to the 4Pro transmitter unit directly without the solar/UV interface?
It is not yet clear to me how the solar cell or the UVM-30A are connected. I am currently using the interface, but I would like to do without it.
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Hello SunDancer,

The 4Pro Transmitter doesn't need the separated Solar / UV interface used on the Pro2 systems, it is already included on the main 4Pro TX board, as said on the description of the 4Pro TX board.
Don't connect the Pro2 Solar / UV interface to the 4Pro TX board, it may damage the Solar /UV inputs.
The solar cell and the UVM-30A should be connected directly to the board.

The transmitter unit can be supplied with voltage via a solar module. If I connect this to the 12V interface and if so, what does the battery look like, is it also connected to the 12V interface and/or do I need a charging module for the battery ?

Yes, if you chose to power the TX through a 12V battery instead of 12V from a mains supply, then the battery should be kept charged, usually through a solar panel and a solar charge controller (I do not recommended this option for your place, as you will need at leat a 50W solar panel).

My last question concerns the TX LED and the fan LED. In the parts list, the FAN LED is specified as a "Blue" LED, the TX LED has no color assigned. Can I also use other colors for the LEDs? As far as I remember, some colored LEDs also have different voltages. Would I have to replace resistor R8 with a different value to change the voltage for the FAN LED?

With little variance on brightness almost all LED colour will work with the default value resistors.

I just had a question about the HTU21 temperature sensor. I wanted to try out a different T/H sensor instead of the SHT31 and the HTU21. I received this sensor:
Si7021 Humidity Sensor Temperature Sensor I2C SHT21 HTU21 GY-21 Sensor Module
Can someone tell me exactly what kind of sensor I have? I can't find any explanation about the sensor on the web. In the firmware for the transmitter unit I can set 1 for SHT21 or 2 for HTU21 for TH Sensor0 and then I get identical values displayed on the serial monitor.

From the picture on the link that sensor seems a HTU21. Its a good sensor but don't last long when used outside.
Using a different kind of sensor than those supported by the software, would imply changes on the software and / or libraries. The STH31 is a pretty good durable and precise sensor, why not use it?

Regards
Werk_AG