Added steps howto build the hardware

docs/hardware/index.md

@@ -3,4 +3,15 @@
 OpenDTU supports the ESP32 family of microcontrollers.
 
 Depending on the inverter to be addressed, different RF modules are required. The HM series requires the NRF24L01+ module, while the HMS/HMT series requires the CMT2300A module.
-Please see the [inverter overview](../hardware/inverter_overview.md) to see if your inverter is supported and to determine the required RF module.
+Please see the [inverter overview](inverter_overview.md) to see if your inverter is supported and to determine the required RF module.
+
+## Steps to build your own DTU
+
+1. Determine the [RF module](inverter_overview.md) you need
+2. Get a ESP32 module.
+3. Use a power suppy with 5 V and 1 A. The USB cable connected to your PC/Notebook may be powerful enough or may be not. Also the quality of the used USB cable might have an impact.
+4. Wire the module and RF module
+5. Wire a optional [display](display.md)
+6. Wire optional [LEDs](led.md)
+7. [Flash](../firmware/flash_esp.md) the firmware via USB
+8. Upload a [device profile](../firmware/device_profiles.md) which describes your hardware (or look at the profile first and connect your pins accordingly) using the [Config Managment](../firmware/configuration/config_settings.md)