Pin Reading High on Disconnect

[ccdubs]

Hi,
I have an issue with an 08m where if I disconnect a wire from the breadboard to input pin 2 of the chip, it seems to register that the pin has gone high. This wire is connected to a push switch which is connected to Vcc. When the wire is connected to the switch it works perfectely, but if i pull the wire out the pin reads high? Isn't this akin to just pushing the switch?

When high my code then pulses a buzzer. Sometimes on the wire disconnect the buzzer pulses once, other times it may pulse several times or indefinitely (my ears haven't allowed it to go that far yet!)

I am using an experimenter board which utilises pull a pull down resister array for all inputs.

Anyone know why this is happening?

 

[inglewoodpete]

The pulldown resistor must always remain connected to the input pin (leg). Due to an input pin's high impedance, an unterminated pin will 'float' at any potential (voltage) if not pulled high or low. This is caused by the effects of electrostatic charges and/or electromagnetic induction.

It's not clear from your description if the pulldown resistor is being disconnected from the PICAXE when you disconnect the wire.
-Peter

 

[ccdubs]

Hi Peter,

The pin is always tied low by a 10k resistor array. The set up i have is the experimentor starter kit.

The design is very similar to the Alarm project that is available on this site.

 

[inglewoodpete]

You'll have to be real specific here. The only 08M <i>experimenter </i> board listed on the rev-ed PICAXE website is the AXE-092 &quot;Schools Experimenter&quot;. Yet you refer to a 10K resistor array which the AXE-092 does not have.

Can you provide your kit/board number?

Also, are you referring to pin 2 (physical leg 5 on the package)?

Edited by - inglewoodpete on 26/09/2006 05:45:43

 

[ccdubs]

The board is an AXE090 which is compatable with all PICAXE chips.

The input is connected to physical pin 6 as per the ASCII art below.

vdd
|
|
|- switch normally open
|
|_______Pin6
|
|
-
|R|
-
|
|
-
GND

 

[inglewoodpete]

Rev-Ed's website does not list the AXE090, so I googled it and found a URL to the PDF document at the Rev-Ed site....

The board looks like a great way to experiment with PICAXEs.

Anyway, from your description of the problem and ASCII diagram, something does not add up. Are you able to test the voltage on the pin with a multimeter? You should also check continuity between the resistor and leg 6 on the experimenter board.

 

[eclectic]

I don&#8217;t have an AXE090, but, having read the datasheet,
page 4 states : -

PICAXE-08 / 08M
The PICAXE-08 input/output connections are on the left hand side of the board,
marked OUT0, I/O1, I/O2, IN3 and I/O4. Note that OUT0 is also connected to
TXD and so will flicker when a download is taking place (PICAXE-08/08M only).

Therefore, are i/o pins 1,2 and 4 left &#8220;free&#8221;, to enable programming?

i.e. you must add your own pull-up / pull-down resistors?

e.

 

[Technical]

To confirm, the AXE090 does not have pull downs on any input pin and os this is certainly the issue here.

However the push switches on the right do have associated pull downs, so if using these switches for testing you just make a single wire connection from the switch pin to the PICAXE input pin.

 

[ccdubs]

I wish technical would have responed a little earlier as I had just figured it out for myself.

I made the mistake of assuming that the pull down resistors were fixed to the pins but they are only connected if using the push button, which I was.

So simple...thanks all and sorry for wasting peoples time.

 

[Technical]

We think 9.05am is a fair response time to a question posted at 2am on a Sunday night (UK time!)

 

[Mycroft2152]

And I thought you guys at Technical lived, ate and slept in your offices!



MycHolmes

 

[ccdubs]

Technical: your response was brilliant, I didn't expect it.

This is my first time dealing with micros and your products have made it very easy for me to understand them.

Well done.