Changes

The signal generator provides the reference sinusoidal signals for the field generator emitter coils.

The waveform generator provides the reference sinusoidal signals for each emitter coil of the field generator. The generator comprises of a single Analog Devices [http://www.analog.com/media/en/technical-documentation/data-sheets/AD9833.pdf AD9833] programmable integrated circuit which provides a reference sinewave at a desired frequency. The IC is programmed over the SPI bus using a microcontroller.

The AD9833 synthesises the reference sine waves for each emitter coil. The integrated circuit is programmed over the serial peripheral interface (SPI) using a microcontroller. On powering up the IC needs to be configured to output the required frequency. The AD9833 contains a set of registers which can be written over the SPI interface.

The full programming sequence is detailed in the datasheet and [http://www.analog.com/media/en/technical-documentation/application-notes/AN-1070.pdf application note]. Typically a microcontroller platform (for example [https://www.arduino.cc/ Arduino] or [http://energia.nu/ MSP430] is used to program each waveform generator when the system powered-on.

The gain stage amplifies the output of the sinewave generator. The output of the AD9833 is capacitively coupled to the input of the [http://www.ti.com/product/TL081 TL081], a general purpose op-amp. The TL081 is configured with a potentiometer to allow the gain of the amplifier to be adjusted.