PCF8591 < Embedded_Systems

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---+ Analogue to Digital and Digital to Analogue Conversion

The [[http://www.nxp.com/documents/data_sheet/PCF8591.pdf][PCF8591]] is a 4 channel analogue to digital (ADC) and 1 channel digital to analogue converter (DAC). ADC and DAC have 8 bit resolution. The PCB card already contains 3 devices that can be connected via jumpers to the ADC inputs:<br /><br />
   * a potentiometer on channel 3
   * a photo resistor on channel 0
   * a thermistor on channel 1
   * channel 2 is free
The sensors are resistors whose resistivity changes with the parameter to be measured (temperature or light intensity) and, in conjunction with a 1 k&Omega; resistor they implement a voltage divider. This voltage is converted to a digital value by the ADC.

There are 2 LEDs on the PCB: a red one showing that the board is powered and a green one connected to the DAC output.

I used the free channel to feed back the DAC output.
| <img alt="pcf8591front.png" height="306" src="%ATTACHURL%/pcf8591front.png" title="pcf8591front.png" width="458" /> | <img alt="pcf8591back.png" height="306" src="%ATTACHURL%/pcf8591back.png" title="pcf8591back.png" width="458" /> |
| pcf8591 front | pcf8591 back |
You can distinguish the PCF8591 chip, the potentiometer and the photo resistor and thermistor. The pins on the left make the connections to external analogue signals and 1 pin provides the DAC output while the pins on the right implement the I2C interface with SCL, SDA, Vcc and Gnd.

Here is the circuit diagram of the PCS:

<img alt="yl-40.jpg" height="396" src="%ATTACHURL%/yl-40.jpg" title="yl-40.jpg" width="516" />

Unfortunately on the boards I purchased in China there is an error on the PCB: The thermistor is not correctly connected to ground. For this reason I only see the value 0xff. A little bridge between the ground pin of the photo resistor and the thermistor will do the trick.

-- %USERSIG{UliRaich - 2017-02-01}%

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Topic attachments
I	Attachment	History	Action	Size	Date	Who
png	pcf8591back.png	r1	manage	1218.9 K	2017-02-04 - 13:13	UnknownUser
png	pcf8591front.png	r1	manage	1096.3 K	2017-02-04 - 13:13	UnknownUser
jpg	yl-40.jpg	r1	manage	37.3 K	2017-02-04 - 14:53	UnknownUser

Topic revision: r4 - 2017-02-05 - uli