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Support Forum » Halloween Project Help

October 27, 2009
by n3ueaEMTP
n3ueaEMTP's Avatar

I am working on duplicating the Halloween project for my Son’s Cub Scout Party on Thursday evening. I can't seem to get the project to work unless I am physically touching the aluminum foil inside the jack-o-lantern. I’m using generic foil. Could that be the cause? I’m considering going to the hardware store & buying some actual aluminum and using screws and eye connectors to make the connection permanent. Any thoughts as to why I need to physically touch the foil? Could it be that I’m dehydrated or is the amount of water in my body not a variable?

Thanks in advance for any help...


October 27, 2009
by hevans
(NerdKits Staff)

hevans's Avatar

Hi n3ueaEMTP,

Glad you decided to try out the Halloween Project. In our labs, we also found that the the sensor could be a bit finicky in some situations. Here are a few things you could try.

  1. Make sure there is plenty of space between the sensor foil, and the ground foil, and that they are placed such that when you reach your hand in you are reaching between the two sheets. In some of our prototypes he had the foil all the way at the bottom of the bowl, and this didn't work as well. When we made the sheet smaller, and placed it towards the front and up towards the lip, it was much more reliable.

  2. Make sure there are no exposed wires that might be touching the sensor from the LEDs.

  3. Make sure you ground pin 12 of the MCU, the one between your sensor and the LED PWM pin. If you don't, the PWM signal can capacitively couple across to your sensor wire.

  4. Use some printf statements and minicom to read the numbers your system is getting. You are most interested in the avg_timer variable. I think there is already printf in the main loop that prints this variable. Observe what this value is when you move your hand in out of the sensor, it if it is not changing enough, you might need to adjust the multipliers that the full and floor variables use. (Warning: connecting the serial port will change the grounding of your system, and your capacitive sensor will behave differently. Take what you learn from this step with a grain of salt)

Let us know if you get it working, and post pictures!


October 31, 2009
by n3ueaEMTP
n3ueaEMTP's Avatar

Humberto, Sorry for the delay. I worked for a bit on Thursday (the deadline for the party) without success. Thanksgiving & Christmas are coming up for hopefully I'll have it working by then. Maybe I'll have a light up turkey or Santa head, who knows? I'll keep you posted. Thanks again for the help.

Chris B.


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