PNS Web Server interface dies

#1
I have a PNS with a Picaxe connected to it. The PNS is powered from the ribbon cable to the Picaxe, so the 9V DC power plug is unused. Everything seems fine, except that sometimes the web interface dies, in that all HTTP connections are then refused. The Picaxe is still able to access the I2C bus to get the time (which keeps advancing, so the clock is ok) and read/write the I2C RAM I have attached. So the PNS is working on the I2C side but not the web interface side.

When the PNS goes into this state, two black blobs appear on the LCD display after the IP address.

With the setup spread out on the bench, and the Picaxe programming interface connected to a PC for debugging, I reckon it happens much more often but I still can't get it to repeat reliably. Disconnecting the serial cable, closing the terminal window etc seem to have something to do with it.

Anyone seen anything similar? Ideas on how to make it more repeatable??

Cheers
Simon
 
#2
I don't have a schematic for the PNS so I'm not sure that you can power it via the 16 way IDC. I would doubt that it was intended to be used this way.

The 5V on the IDC is to allow the PNS to provide power to the PICAXE and not the other way. There may be some protection diodes or other circuitry to prevent you trying to do this.

The two power options are

1. PNS uses 9V connector, PICAXE uses 5V from PNS
2. PNS uses 9V connector, PICAXE uses external power

If you are using the the AXE022 then jumper J3 must be set accordingly.
If you are using your own PICAXE board then you will need to make your own provision for switching between PNS and external power.

As for the black blobs, I've seen that too. I think it's when the PICAXE is attempting to write to the screen and failing. I was trying to get a 40X2 working on the AXE022 and this is when I saw the blobs. I put back the original 28X and all was well again. Most likely its an I2C problem.
 
#3
Don't have floating inputs!

I've finally found the reason for the random behaviour and "black blobs". I had foolishly left an input floating on the PicAxe that was behind the PNS. As "everyone knows" this is a very bad thing to do, but I just overlooked it for ages.
My guess is that the floating input would randomly disrupt the PicAxe firmware causing it to randomly access the I2C bus and mess up the PNS / LCD.
Anyhow, two minutes pulling the unused inputs up with a resistor fixes it. The system is now completely stable.
 

sbscott

Senior Member
#4
Simon,
You mentioned " left an input floating on the PicAxe that was behind the PNS" in your last thread. What inputs are you talking about? I am having the same symptoms with my PNS/PICAXE setup.

Thanks for your help!
 
#5
I was interfacing a PICAXE-28X to the PNS. I was using 7 of the 8 inputs - all except IN2 - for various serial inputs and to control the I2C PNS bus. IN2 (leg13) was not connected to anything, but I failed to notice despite staring at the circuit diagram and circuit board for ages. The fix was to simply connect IN2 to +5 via a resistor (10k or 22k at a guess).

If anyone wants to read about pull-up resistors, try here: http://everything2.com/title/Pull-up+resistor or, for a hard core discussion, here: http://www.interfacebus.com/IC_Output_Input_Pullup_Resistor_Values.html
 
Top