All, in pursuit of my DCS World A10C cockpit build, I have made the countermeasures panel that you can see in the picture. I have used 3off 8 X 1 LCD displays, which are driven by PCF8574 modules set to have different addresses. These are all connected to one Nano board. Power for the LCD modules is via the PCF boards, and the 5v and GND are shared as the PCF boards receive the VCC and DNG from the Nano, which ultimately gets power via the USB connection.
As you can see it works, but the problem that I have seen is that as I added the extra displays, the displays are getting fainter, with less contrast available. I have used the pots on the PDF8574 modules to maximise the contrast, but it really doesn't help much.
Should the PCF boards have separate power supplies and if so should it be common to the Nano or is there something else I should do
OK, thanks - so to confirm for a mechanical engineer, not an electronics savvy guy, I should be seeing the full 5v and so I have a short or partial short to find?
I just checked everything, including the bare Nano board - the '5v' output is only 4.5. With just one of the PCF boards and LCD modules connected it drops to 4.38 (doesn't matter which one). With two PCF boards it drops to 4.22v
To test I disconnected all the other hardware so that there was no chance of each affecting the other
Lesthegringo:
Should the 5v supply be externally supplied?
It sounds as if your USB voltage is sagging badly (which is not infrequently the case). There is also a diode in the Nano which drops at least 0.6 Volt between the USB input and the 5 V pin.
You need a good regulated 5 V supply. A "Phone charger" which is often rated at 1 Amp would be one option and connecting direct to the "5V" pin along with all the displays eliminates the voltage drop in the diode.
No, it's not a short circuit. You could call it a "partial short" but really it is just that the displays are drawing more current than the USB supply is coping with.
