Hello,
My objective is to use the AT42QT1012 - Standalone Toggle Capacitive Touch Sensor Breakout as a on/off switch for an 8x8x8 LED Cube project. While reading the breakout sensor tutorial, I noticed that the picture with the simple motor had a mosfet, a few capacitors, and a diode being used. I'm unsure where the capacitors and diode connect and their values. Can you please illuminate this part of the project for me? Also, is this the mosfet that I need to purchase? http://www.adafruit.com/products/355#Technical_Details
Thanks a lot for any help!
Capacitive Touch Sensor / Power switch
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adafruit_support_mike
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Re: Capacitive Touch Sensor / Power switch
The only schematic for a motor I found was this one:
It only shows three components: a motor, a mosfet, and a diode.
The symbol at the bottom, surrounded by G, D, and S, is all a single device: the mosfet. A mosfet has a strip of silicon between the D (drain) and S (source) pins, and the amount of current that can flow through the silicon is controlled by the voltage on the G (gate) pin. There's a layer of glass about three atoms thick between the channel and the gate, so that part of the mosfet is basically a capacitor. It's traditional to represent doped silicon with an arrow, and the left-pointing arrow says the mosfet's channel is made of N-type silicon.
It's very easy for a spark to blow a hole through the thin layer of glass between the gate and the channel, destroying the mosfet. Mosfets had a reputation for being absurdly fragile for many years because of that. Eventually designers learned that they could eliminate most of the problems by building a diode into the mosfet between the S and D pins. The internal diode doesn't do anything when the mosfet operates normally, but it routes current away from the delicate gate-channel barrier when power is connected the wrong way.
The only real diode in the schematic is the one in parallel with the motor, and that's called a 'snubber diode'.
The only difference between a motor and a generator is where you apply the power. If you send current through the coils and use the rotation of the shaft to drive a load, you have a motor. If you turn the shaft mechanically and take current from the coils, you have a generator.
That's important when you use PWM to control a motor. Every time you cut the power to the coils, you have a rotating armature in a magnetic field. The device stops being a motor and becomes a generator, forcing current to move. Ohm's law says voltage equals current times resistance, so if you induce current in a coil with very high resistance between the ends, you get very high voltage. In practice, the voltage rises until it becomes high enough to arc across an air gap or short out some component in the circuit.
The snubber diode gives the induced current a low-resistance path to follow. It prevents voltage spikes that can damage switch contacts with arcing or kill other components.
- mosfet_motor.gif (2.99 KiB) Viewed 158 times
The symbol at the bottom, surrounded by G, D, and S, is all a single device: the mosfet. A mosfet has a strip of silicon between the D (drain) and S (source) pins, and the amount of current that can flow through the silicon is controlled by the voltage on the G (gate) pin. There's a layer of glass about three atoms thick between the channel and the gate, so that part of the mosfet is basically a capacitor. It's traditional to represent doped silicon with an arrow, and the left-pointing arrow says the mosfet's channel is made of N-type silicon.
It's very easy for a spark to blow a hole through the thin layer of glass between the gate and the channel, destroying the mosfet. Mosfets had a reputation for being absurdly fragile for many years because of that. Eventually designers learned that they could eliminate most of the problems by building a diode into the mosfet between the S and D pins. The internal diode doesn't do anything when the mosfet operates normally, but it routes current away from the delicate gate-channel barrier when power is connected the wrong way.
The only real diode in the schematic is the one in parallel with the motor, and that's called a 'snubber diode'.
The only difference between a motor and a generator is where you apply the power. If you send current through the coils and use the rotation of the shaft to drive a load, you have a motor. If you turn the shaft mechanically and take current from the coils, you have a generator.
That's important when you use PWM to control a motor. Every time you cut the power to the coils, you have a rotating armature in a magnetic field. The device stops being a motor and becomes a generator, forcing current to move. Ohm's law says voltage equals current times resistance, so if you induce current in a coil with very high resistance between the ends, you get very high voltage. In practice, the voltage rises until it becomes high enough to arc across an air gap or short out some component in the circuit.
The snubber diode gives the induced current a low-resistance path to follow. It prevents voltage spikes that can damage switch contacts with arcing or kill other components.
Please be positive and constructive with your questions and comments.