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1300 Henley Court Pullman, WA 99163 509.334.6306 www.digilentinc.com PmodCDC1 Reference Manual Revised December 17, 2015 This manual applies to the PmodCDC1 rev. B Overview The Digilent PmodCDC1 demonstrates capacitative-to-digital conversion through the use of Analog Devices AD7156. With its high input sensitivity and adaptive threshold capability, this Pmod is able to easily handle variance in environmental changes while still reporting accurate information. Features include: Two capacitive input channels Fixed or adaptive threshold capability High sensitivity up to 3 fF Small PCB size for flexible designs 2.3 0.8 (5.8 cm 2.0 cm) 24-pin connector with I2C interface Follows Digilent Pmod Interface Specification The PmodCDC1. 1 Functional Description The PmodCDC1 utilizes a 12-bit capacitance-to-digital converter (CDC) to determine if the measured capacitance on a particular channel (conveniently labeled as BTN1 and BTN2 on the Pmod surface) is above, below, inside, or outside a user definable threshold level(s). Users are able to read the digital capacitance level on the most recently converted channel through I2C or can simply use the output pins on header J2 if they are only interested in knowing if a threshold has been crossed or not. 2 Interfacing with the Pmod The PmodCDC1 communicates with the host board via the IC protocol. The byte consisting of the 7-bit address for the on-board chip is 0x90 (10010000) for a write command and is 0x91 (10010001) for a read command. On power-up the Pmod enters into continuous conversion mode with both of the channels alternately reporting their data. It also uses the adaptive threshold mode where the output is active (high) only when the sensed capacitance is lower than the difference of the average measured capacitance and the sensitivity (a sensitivity of Copyright Digilent, Inc. All rights reserved. DOC : 502-247 Page 1 of 3 Other product and company names mentioned may be trademarks of their respective owners. PmodCDC1 Reference Manual about 12 fF). Users can choose to either detect when the output of a channel crosses its threshold by watching its respective output pin on header J2 for a high voltage or can get more specific information by querying the device through the IC interface. 2.1 Example: Continuous Read with Default Settings A communication transmission example taking advantage of continuous read capability and reporting the contents of the Status (address 0x00), most recent Channel 1 and Channel 2 data, and average Channel 1 and Channel 2 data registers, is shown below. The bit names are taken from the Analog Devices datasheet and are defined after the table. Command byte Address byte 1 0 0 1 0 0 0 1 (ACK) 0 0 0 0 0 0 0 0 (ACK) 1 Status PwrDown DacStep2 OUT2 DacStep1 OUT1 C1/C2 RDY2 RDY1 (ACK) 2 Ch 1 Data High Ch 1 Data Low b11 b10 b9 b8 b7 b6 b5 b4 (ACK) b3 b2 b1 b0 0 0 0 0 (ACK) Ch 2 Data High Ch 2 Data Low b11 b10 b9 b8 b7 b6 b5 b4 (ACK) b3 b2 b1 b0 X X X X (ACK) Ch 1 Avg High Ch 1 Avg Low b11 b10 b9 b8 b7 b6 b5 b4 (ACK) b3 b2 b1 b0 0 0 0 0 (ACK) Ch 2 Avg High Ch 2 Avg Low b11 b10 b9 b8 b7 b6 b5 b4 (ACK) b3 b2 b1 b0 X X X X (ACK) Status Register Bit Values Bit Mnemonic Description 7 PwrDown PwrDown = 1 indicates that the part is in a power-down DacStep2 = 0 indicates that the Channel 2 CAPDAC value was changed after the last CDC 6 DacStep2 conversion as part of the auto-DAC function. The bit value is updated after each finished CDC converion on this channel. OUT2 = 1 indicates that the Channel 2 data (CIN2 capacitance) crossed the threshold, according 5 OUT2 to the selected comparator mode of operation. The bit value is updated after each finished CDC conversion on this channel. DacStep1 = 0 indicates that the Channel 1 CAPDAC value was changed after the last CDC 4 DacStep1 conversion as part of the auto-DAC function. The bit value is updated after each finished CDC converion on this channel. OUT2 = 1 indicates that the Channel 1 data (CIN1 capacitance) crossed the threshold, according 3 OUT1 to the selected comparator mode of operation. The bit value is updated after each finished CDC conversion on this channel. C1/C2 = 0 indicates that the last finished CDC conversion was on Channel 1. C1/C2 = 1 indicates 2 C1/C2 that the last finished CDC conversion was on Channel 2. RDY2 = 0 indicates a finished CDC conversion on Channel 2. The bit is reset back to 1 when the 1 RDY2 Channel 2 data register is read via the serial interface or after a part reset or power-up. RDY1 = 0 indicates a finished CDC conversion on Channel 1. The bit is reset back to 1 when the 0 RDY1 Channel 1 data register is read via serial interface or after a part reset or power-up. 1 The bits of the status register are defined in their own table (from the Analog Devices datasheet). 2 The last four bits of each data set are not part of the 12-bit data conversion and so are either 0 s or don t cares (X) Copyright Digilent, Inc. All rights reserved. Page 2 of 3 Other product and company names mentioned may be trademarks of their respective owners.