N0-G0 Disconnected From Download Cable

[Logic Rules]

Hi Guys,
I’m having a problem with my 08M disconnected from the download cable.
I’m attempting to run the bike indicator program at http://www.nexusresearchgroup.com/technical_data/bike_indicator.bas
As long as the download cable is connected all is well but when disconnected the LEDS begin to flash, and the Piezo sounds off.
It seems as if there is some sort of sensitivity issue here: if I remove the leads to the inputs all becomes quiet again. If I get too close (1/2” – 1”) to the terminals the device will fire up.
I have tried the same circuit on my 18X, and the results are the same.
I don’t have any shielded wire to try; if in fact that would help.
I am using P. Andersons’ kit boards.
Anybody know how to fix this?

 

[hippy]

Sounds like you've got something floating, quite possibly the 10K/22K download interface doesn't go to 0V.

 

[Logic Rules]

Hi Hippy, Nope that's not it they are both soldered in quite firmly, and effectively. Is it possible there is something wrong with the schematic for the boards?

 

[inglewoodpete]

As hippy has implied, there is a hardware problem. Is the PCB a home-designed one?

You should always do a hardware check before plugging the PICAXE and connecting the supply.

Do the following:
- Disconnect the power/battery from the PCB
- Unplug the PICAXE chip
- Leave other inputs/outputs connected to the PCB
- Using an ohmmeter or multimeter on a high ohms range (Eg 2 Megohms),
Check that each input, including the download pin, has a readable* resistance to either the 0v power connection or the +5v power connection. For a start, the Serial-In (download) pins should show about 32kohms to 0v. *Typically less than 500kohms

As hippy said, no input should be left floating (open circuit) at any time.

 

[Dippy]

All of the above.

"Is it possible there is something wrong with the schematic for the boards?"
- why don't you get on to P.Anderson and ask?

Have you got thr schematic you can post?

As Pete asks; is it a homebrew PCB?

Honestly (and with delicacy and the greatest sensitivity, respect and diplomacy) I'd check your own board before thinking that an experienced person like Phanderson has messed up. Nothing is impossible of course.... and tpyos can slip through.

 

[BeanieBots]

First instinct is that the serin pin is left floating as suggested but you have ruled that one out and as pointed out by Dippy, it is unlikely that the board is faulty by design.
The fact that things change by proximity DOES indicate an open input &/or serin.
Your program relies on input switches to work correctly. Check that the pull-up resistors are fitted correctly.
When the serin cable is fitted, there is small amount of current which flows. This can cause very light conduction on inputs which has a similar effect to a very high value pull-up resistor making it harder to spot if one has not been fitted.

 

[papaof2]

I use Peter Anderson's 08 and 18 kit boards and they work very well - whether connected to a breadboard on the bench with multiple fluorescent lights overhead or measuring water flow a few feet away from a small electric water pump.

I vote for "unterminated inputs" as the source of the problem. Active inputs should have proper pull-up/pull-down resistors (depending on how they are used) and unused inputs should have a pull-down resistor. These resistors are very inexpensive insurance against "What the #$@&#@ is going on?" events.

John