In keeping with the modular design that enables costs to be kept to a minimum without compromising on capabilities, a standalone mode of operation is being added to the firmware.
This will display a few basic measurements such as capacitances, voltages, frequencies etc on an ssd1306(128x64) OLED if it is detected on the I2C port when the device powers up. The device can be run off of batteries or other power sources.
Once it receives data from the PC, it will automatically exit the standalone mode and a remote/hard reset will be required to restore it.
The Picture Above shows the present state of development of the standalone mode.
Polynomial based calibrations are not applied , and instead nominal values for references are used.
CH1,CH2 are floating, and are displaying a few fluctuating readings. The capacitance of 1uF capacitor is calculated using constant voltage charging mode, and the potential developed across it at the end of the charge cycle is also shown. If a diode is plugged in instead of a capacitor, this voltage approximately represents the barrier potential.
The frequency of the clock fed to the AD9833 DDS is also measured. However, since the clock source is correlated to the 12MHz TCXO that is also used as a reference for the frequency counter by means of a PLL, the readout may have an error of up to 2.5ppm as stated in the datasheet of the FOX924b 12MHz TCXO.
The display projecting out awkwardly isn't a good solution, so a centrally placed four pin I2C header has been added to the next layout sent for fabrication.