Touch sensor problem - High resistance with opened switches

[ricardocrl]

Hi,

The topic may be simplistic. In my newer vending machine creation, I have the following scenario:



Some things are hard to understand why the h*ll did I need to do that way... The machine can be seen here: http://www.youtube.com/watch?v=WUItzPTetpc
The 9V end on the right is for the coin conductivity detection. It has one extra old electric plate, but I think it doesn't matter that much to evaluate the problem.

I know I'm pushing a little bit the limits, but I'd like to know your idea of what can be the weakest point in the layout, that may be producing high resistance value on the input (around 400 or more). The value also oscilates sometimes...

Assume that the custom NXT-NXT connectors are correctly built. I'm pretty sure they are... I'm using a PCB and mindsensors sockets.

I'm using mindsensors enhanced firmware, for longer wiring connections (which I believe to only help for the I2C connections).

Ricardo

[mightor]

Hey Ricardo,

The wires may be picking up inductance from outside.
Is there a reason you can't connect each touch switch directly to the SMUX?
Do you see the problem when you remove one or more parts from this circuit?

To debug something like this, I would simply disconnect all of it and then build it up slowly and see when the problem starts again.

- Xander

[ricardocrl]

Hi Xander,

Is there a reason you can't connect each touch switch directly to the SMUX?

Well, yes, everything is in use. Every port of the NXT and multiplexers. Touch sensors were always sensors I tried to "split" as a way to increase the available ports. As far as they are never pressed at the same time, this works fine.

Do you see the problem when you remove one or more parts from this circuit?
To debug something like this, I would simply disconnect all of it and then build it up slowly and see when the problem starts again.

Unfortunately, I don't have the machine with me right now. I will fine tune it before LW, when I get back to Sweden. For now, I'm planning to take parts and wires with me and studying the problem.
But I barely remember that I only noticed this problem, when I joined the 1,5m cable to the network.

I asked a professor that thought about ohmic resistance, along all the connections. What do you think? My guess is that, once the circuit is opened, this shouldn't be having any effect. Only when we close the circuit, it could be showing a higher value than...~180.