ARDUINO am KNX

[sx3]

Hello,

How much current can I draw from the Siemens BTU?
Is it possible to Power the MEGA 2560, from the BTU?
The only thing the MEGA will Power is opto-coupler for TTL Communication with an IVT heat pump.
It would be great if I could Power the Mega from the BTU, instead of using opto-couplers in between because of external Power supply.

[Eugenius]

Siemens BCU has 5V 50mA output.
MEGA needs up to 100 mA => it can be started, but unstable (i've test it, bad idea )

[sx3]

Thanks, thats a shame!
Did you use optocouplers when powered the MEGA externally? Or is it enough with Rx/Tx without any problem?

[Eugenius]

yes, i use ADUM1201 for that.

[sx3]

Thanks, wow that was a fast coupler, I have a couple of MCT6 at home I will test with, hopefully they are fast enough för 19200 Baud.
Any pictures / schematics of your Mega?

[Eugenius]

No, but it was something like thit:

ADUM Pin 1 (VDD1)    <->    +5V BCU
ADUM Pin 2 (TX 1)    <->    RX BCU
ADUM Pin 3 (RX 1)    <->    TX BCU
ADUM Pin 4 (GND1)    <->    GND BCU

ADUM Pin 8 (VDD2)    <->    VCC Arduino
ADUM Pin 7 (RX 2)    <->    TX Arduino
ADUM Pin 6 (TX 2)    <->    RX Arduino
ADUM Pin 5 (GND1)    <->    GND Arduin

[sx3]

Thanks mate! You did use resistors right? what size, and to which pin?
Do you perhaps have a schematic for the connection?

[tuxedo]

Question is: Why do you want to use the mega? Isn't any other arduino sufficient? Or is it just about the 2nd serialport?
How about Arduino Zero? --> https://www.arduino.cc/en/Main/ArduinoBoardZero

MOre powerful, more energie efficient and can be powered via BCU.

[sx3]

It's because of the serial ports. The arduino will be a gateway between my heat pump and KNX. Hence 2 HW serial needed + 1 extra to monitor, during testing and programming.
Plus I wasn't sure if the Zero memory would have been sufficent to build this gateway.

[tuxedo]

The Zero has

Flash Memory	256 KB
SRAM	32 KB

That's more than you need. Regarding multiple serial ports, read --> https://learn.adafruit.com/using-ats...ports?view=all

For testing/Programming the Zero has a dedictated debugger port. With that (and Atmel Studio) you can step line-by-line through your code. That's far better than serial console debugging.

[sx3]

Hmm, maybe the Zero is interesting after all.. Where did you find info on the serials? I didn't manage to find it when I looked up the boards Before.
How many mA will the Zero draw from the KNX Power supply?

[tuxedo]

Info about the serials came from samd21 datasheet + google.

I have no exact power consumption. But our KONNEKTING team mate Masifi is already using the SAMD21 direclty on KNX (but with self assembled NCN5120 KNX Transceiver instead of Siemens BCU).

[sx3]

Alright, I might consider the Zero for final version.
For now, I Think I go for the Mega, If someone could help me out with schematic/diagram between Ardu-serial and KNX-uart using MCT6 or ILD2, I would be very glad.

[Eugenius]

Alright, I might consider the Zero for final version.
For now, I Think I go for the Mega, If someone could help me out with schematic/diagram between Ardu-serial and KNX-uart using MCT6 or ILD2, I would be very glad.

Example:
http://rago600.sourceforge.net/generic_com.pdf

[sx3]

Thanks, but that optocircuit is "inverted" and intended for CMOS 4000 TTL signals. Rego600 have one signal 3V3 and second 5V; one signal is inverted and
second not.

I'm not sure that either Arduino or the Siemens BCU is using this type of TTL's
As you can see on that schematic, the circuit is different on each side of the optocoupler.
Do you still think it would work with Arduino->KNX?