LowPowerLab Forum

Hardware support => ATXRaspi => Topic started by: djanice1980 on June 28, 2016, 06:02:58 PM

Title: Instead of a power switch - I want to use a capacitive touch sensor [solved]
Post by: djanice1980 on June 28, 2016, 06:02:58 PM
I am trying to turn on/off the ATXRaspi using a capacitive touch switch from adafruit.

https://www.adafruit.com/product/1374

I know it sends 5v out so I think I need to use a mosfet or a relay to turn on ATXRaspi.  I went to the store and purchase an n-channel enhancement mode mosfet model NTE66.

http://www.nteinc.com/specs/10to99/pdf/nte66.pdf

I can get it to power on the ATXRaspi but It won't power off when holding the "button" (sensor).  I think I may be wiring something wrong.  I don't have much experience with mosfets so I may need a little help.  I got the LED on the touch switch wired in fine and I am thinking I need to possibly put a resistor somewhere.  What I would like to do is attach the sensor to my case and then I can wave or touch the outside of the case instead of pressing a button.

Any help would be appreciated.

Thanks




Title: Re: Instead of a power switch - I want to use a capacitive touch sensor
Post by: Felix on June 28, 2016, 10:03:24 PM
If it turns it on, the reset/off is the same thing, but the hold time is longer.
Title: Re: Instead of a power switch - I want to use a capacitive touch sensor
Post by: djanice1980 on June 29, 2016, 12:14:30 AM
Yea I thought that too but it refuses to turn off no matter how long I hold it.  I removed the switch and mosfet then used a short piece of wire to short the button contacts and it turns off properly.  I'm thinking I just have something wired wrong.

The "button" has 5v, out, gnd, and led pads.  I soldered the 5v to "+" on the bottom of atxraspi then soldered gnd to led - (btw I think I also have it soldered to "-" on the bottom of atxraspi.  Then led is soldered to led +.  The out is soldered to gate on the mosfet and drain and source are soldered to both button pads.
Title: Re: Instead of a power switch - I want to use a capacitive touch sensor
Post by: Felix on June 29, 2016, 11:49:13 AM
An N-channel is switching the low side, not the high (VCC).
Since one side of the switch is connected to VCC and the other to the MCU, you might need a P-Fet to do this  ::)
Title: Re: Instead of a power switch - I want to use a capacitive touch sensor
Post by: djanice1980 on September 02, 2016, 02:31:39 AM
Just wanted to let you know I got this working.

I used an enhanced n-fet but I had to reverse the drain and source so the load was on the drain side.  Then I had to get two resistors for the gate.  One to power from the capacitive touch sensor and one to ground to drain the gate when I stop touching the sensor.

Everything works great!  Thank you for your insight.