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Topic: My Nano circuit works powered by FTDI, but not VCC/GND. What could I be doing? (Read 360 times) previous topic - next topic

davepl

I built a small dedicated nano circuit that controls an old Noritake Itron VFD.  Works great.  So I wanted to expose it as a slave i2c device. 

My problem is that if I power it up by supply 5V to Vcc and GND to GND, it boots (LED on) but nothing happens.

If I power it up by connecting the 5V FTDI breakout, the VFD works. 

I tried removing all Serial references in case it was hanging on output, but to no avail.

What could be different in so far as being connected to a serial breakout makes it WORK?

If I plug the USB cable into a power brick it works also, so the difference seems to be either having the board connected or being powered through it, but it's not communicating with anything (as proven by working with just a power brick and not the PC connected).

Any idea are welcome!

DrAzzy

Are you reading from the serial port? If so, try pulling the RX pin up to Vcc or removing calls that read the serial port - if there's nothing connected to RX, it will float, maybe it's picking up noise that's interpreted as a barrage of garbage characters (and crashing your serial input processing code) - those VFDs contain a boost converter, which could conceivably be the source of the noise in question.

You say the LED is on. Do you mean the power LED, or the pin-13 LED? The power led comes on whenever there's power, regardless of the state of the chip. I would upload a sketch that blinked the LED or something.

Check the voltage on on the Vcc, Gnd, and Reset pins of the chip, too.

Are you using a Nano or a Pro Mini? I am confused by your terminology. If you are using a nano, why would you need an FTDI breakout board? There is an FTDI chip built into the nano, connected to the USB port... What happens when you use that? The pro mini does not have an on-board FTDI chip, and would make sense to use with an FTDI breakout board.
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dmjlambert

The most common thing forgotten about any type of serial communication, whether it is i2c, regular serial, SPI, is that ground is one of the necessary connections.   Even tutorials like this one at Sparkfun don't show the ground wire.   It even says in the tutorial "I2C requires a mere two wires", but that is not the case.   It requires 3, SDA, SCL, and GND.   Just like serial requires RX, TX, and GND.      I have seen cases here on the forum (and done it myself) where powering via a serial device such as FTDI or built-in USB makes a circuit work that otherwise shouldn't work, because it completes a ground path accidentally.   So, anyway I'm apparently just going on and on too much, check to see if you have the ground connected between devices.   

davepl

Thanks.  I don't even have a second device yet, this was just getting the Master set up.  It was up and running and working fine, so when I sent to set up the second unit, I unplugged the serial board and found it did not work.

In addition to GND there's a Vcc pin there on that serial header as well, and I need to check the datasheet to see what those pins map to and if they're required, I guess.

wilykat

VFD tended to draw a lot more power than comparable LCD. If you're running off battery or a 5v supply with fairly low max current, the whole project may not be receiving enough power to work properly.

davepl

So here's the answer in the form of another question!  Here's the pinout of the Mini:

http://www.dominicdube.com/wp-content/uploads/ProMiniPinout.png

The FTDI header has a VCC, but its a second VCC.  Could it require that BOTH are connected, or could the one on the FTDI header be special that it MUST be connected?

jremington

What does the Pro Mini pinout have to do with the Nano in the title of your post?

Normally Vcc is one common connection, possibly with multiple pinouts. It certainly is that way on the Pro Mini. On the Nano, perhaps you have a bad connection, so check for continuity.

ChrisTenone

What are you using to supply the 5 volts when you connect it directly? Like Wilykat in reply #4, I think it's the power, not the internal circuitry of the nano.

And it is a nano, right, not a pro mini? If you have a usb on the board, it's a nano. They also have the connectors for FTDI.
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davepl

Correct, it is indeed a Nano with the onboard USB.  I got the naming backwards because I assume the board with the fewer features (no USB) would have the smaller sounding name (nano).

I did notice that when I supplied Vcc to the pin on the FTDI header that the power LED came on, so it might be required.

larryd

No technical PMs.
The last thing you did is where you should start looking.

ChrisTenone

Correct, it is indeed a Nano with the onboard USB.  I got the naming backwards because I assume the board with the fewer features (no USB) would have the smaller sounding name (nano).

I did notice that when I supplied Vcc to the pin on the FTDI header that the power LED came on, so it might be required.
The 5 v on the side of the board is connected to the 5 v on the 6 pin connector at the end of the board (which technically is an ICSP connector, not an FTDI connector.)
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6v6gt

Quote
My problem is that if I power it up by supply 5V to Vcc and GND to GND, it boots (LED on) but nothing happens.
Which pin on the Nano are you treating as Vcc ? Vin or 5v or what? If the supply is 5v then it should be 5v.

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