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pmod:pmoddpot:reference-manual [2022/09/13 17:40] – changed forum.digilentinc.com to forum.digilent.com jeff.greenberg_ni.compmod:pmoddpot:reference-manual [2022/10/04 11:38] (current) – external edit 127.0.0.1
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 +====== Pmod DPOT Reference Manual ======
 +The Digilent Pmod DPOT is a digital potentiometer allowing users to set a desired resistance anywhere from 60 to a nominal 10 kΩ.
  
 +{{Digilent Image Gallery 
 +| image = {{:reference:pmod:pmoddpot:pmoddpot-0.png?direct |}}
 +| image = {{:reference:pmod:pmoddpot:pmoddpot-1.png?direct |}}
 +| image = {{:reference:pmod:pmoddpot:pmoddpot-2.png?direct |}}
 +| image = {{:reference:pmod:pmoddpot:pmoddpot-3.png?direct |}}
 +}} 
 +
 +== Download This Reference Manual == 
 +  * {{:reference:pmod:pmoddpot:pmoddpot_rm.pdf| PDF}}
 +
 +----
 +
 +===== Features =====
 +  * Digital potentiometer with 8-bit resolution
 +  * Select desired resistance from 60 Ω to 10 kΩ
 +  * 6-pin Pmod port with SPI interface
 +  * Follows Digilent Interface Specification Type 2
 +
 +----
 +=====Functional Description =====
 +The Pmod DPOT utilizes [[http://www.analog.com/media/en/technical-documentation/data-sheets/AD5160.pdf|Analog Devices' AD5160]] to digitally set a desired resistance between two terminals. With 256 possible step values, a  resistance between 60 Ω and 9961 Ω can be programmed. The wiper terminal has an internal resistance of 60 Ω.
 +
 +----
 +===== Interfacing with the Pmod=====
 +The %%Pmod DPOT%% communicates with the host board via the [[pmod:communication_protocols:spi|SPI protocol]]. By bringing the Chip Select (CS) line low, users may then provide 8-bits of data on the falling Serial Clock (SCLK) edge in SPI Mode 0. Once the 8 bits of data have been transferred, the rising edge of the CS line loads the data into the internal register %%DAC%%, whereupon the resistance between terminals is set. 
 +
 +The %%Pmod DPOT%% can be utilized in two different styles: a rheostat where users set a desired resistance between one outside terminal and the wiper terminal or in a voltage divider mode where the two outside terminals are powered at set voltages and a ratio of resistance is specified. 
 +
 +Equations for the programmable resistance values and output voltages are provided from the [[http://www.analog.com/media/en/technical-documentation/data-sheets/AD5160.pdf|AD5160 datasheet]] below:
 +
 +{{ :pmod:pmod:dpot:PmodDPOT_rwbEquation.png?450 |Equation for the resistance between the wiper terminal (W) and the B terminal, where D represents the sent 8-bit value in decimal}}
 +Here, R<sub>AB</sub> represents the nominal resistance of 10 kΩ and R<sub>W</sub> is the wiper terminal resistance of 60 Ω.
 +
 +{{ :pmod:pmod:dpot:PmodDPOT_rwaEquation.png?450 |Equation for the resistance between the wiper terminal (W) and the A terminal, where D represents the sent 8-bit value in decimal}}
 +Here, R<sub>AB</sub> represents the nominal resistance of 10 kΩ and R<sub>W</sub> is the wiper terminal resistance of 60 Ω.
 +
 +{{ :pmod:pmod:dpot:PmodDPOT_voltageDivider.png?450 |Equation for the output voltage of the wiper terminal (W) in the voltage divider setup, where D represents the sent 8-bit value in decimal}}
 +Here, R<sub>WA</sub> and R<sub>WB</sub> are the resistances calculated in the two above equations and VA and VB are the voltages applied at terminals A and B, respectively.
 +
 +Care must be taken to ensure that current flow between the wiper terminal and either terminal A or B must be limited to a pulsed ±20mA or a continuous 4.7mA so that the power dissipation capabilities of the on-board chip is not exceeded.
 +
 +==== Pinout Description Table ====
 +^  Pin  ^  Signal  ^  Description             ^
 +|  1    |  ~CS     |  Chip Select             |
 +|  2    |  MOSI    |  Master-Out-Slave-In     |
 +|  3    |  (NC)    |  Not Connected           |
 +|  4    |  SCLK    |  Serial Clock            |
 +|  5    |  GND     |  Power Supply Ground     |
 +|  6    |  VCC     |  Power Supply (3.3V/5V)  |
 +
 +
 +
 +Any external power applied to the %%Pmod DPOT%% must be within 2.7V and 5.5V; however, it is recommended that Pmod is operated at 3.3V. Users must also ensure that any voltage applied to the outside terminals is between GND and VCC.
 +----
 +===== Physical Dimensions =====
 +The pins on the pin header are spaced 100 mil apart. The PCB is 0.9 inches long on the sides parallel to the pins on the pin header and 0.8 inches long on the sides perpendicular to the pin header.
 +----
 +===== Additional Information =====
 +The schematics of the %%Pmod DPOT%% are available {{reference:pmod:pmoddpot:pmoddpot_sch.pdf|here}}. Additional information about the %%digital potentiometer%% including specific timings of the chip can be found by checking out its datasheet [[http://www.analog.com/media/en/technical-documentation/data-sheets/AD5160.pdf|here]]. 
 +
 +Example code demonstrating how to get information from the %%Pmod DPOT%% can be found [[pmod:pmoddpot:start#example_projects|here]]. 
 +
 +If you have any questions or comments about the %%Pmod DPOT%%, feel free to post them under the appropriate section ("Add-on Boards") of the [[https://forum.digilentinc.com/|Digilent Forum]].