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An output power display for my solar system.

G2553 Launchpad,  Blue 4-digit LED display, RS485 Transceiver SN65HVD12P (a low power, 3.3V version of the standard SN75176), this is all there is.

All pins are used,

4 + 7 for the multiplexed LEDs (no resistors: Blue LED, 3.6V supply, output resistance of the pins limit the LED current)

3 pins for UART and send/receive for the SN65.

2 pins for 32768Hz  xtal (I had this one soldered in on the LP, so why not use it)

The MSP asks the inverter over RS485/Modbus "what is your current output power". After less than half a sec, the  inverter aswers with the required value. This repeats every 2 seconds.

The inverter is a Fronius Symo, with Datamanager 2 (which I guess is an embedded linux machine, covering LAN, Wifi, Modbus.....).

The communication protocol can be downloaded from the Fronius website (after signing in), so no reverse engineering was required.

Instead of only power, I could also display line voltage, frequency, total delivered energy....


This is just a working prototype on Launchpad, I will do a PCB later, I also plan to power this directly from the inverter (which has a 12V solar powered output for such things).

See the picture, almost 7.5kW :-)



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Yep, a great application.

May I inquire :   are you muxing the LED array one digit  -or-  one SEGMENT per digit at a time ?   Any the 'ON' time ?   Just curious how much current the IO pins can supply, it sounds like there's no series limiting resistance, which is perfectly OK.





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it is classic LED multiplexing, rows and columns. 

I measured around 20mA in total when 3 digits are on, so this is an average current of  around 1.2mA per LED (most numbers have around 5-7 segments on).

Only one column driver is active high at a time, I go through the four of them with 64 Hz repetition, to avoid flicker. 

The "1s" are somewhat bright than the "fuller" numbers.

For sure I would add resistors (at the segments, not the rows) if using a red or yellow display.

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