4.5 KiB
PCF8591
Arduino Library for PCF8591 I2C 4 channel 8 bit ADC + 1 channel 8 bit DAC.
Description
warning during tests I could overclock the PCF8591 chip up to 650 KHz. However it is only specified to run at 100 kHz. After some time it was getting pretty hot and it broke down. So overclocking is fun but not recommended.
PCF8591 has one 8 bit ADC on board for 4 channels. The ADC is 8 bit and quite fast.
At 100 KHz one gets > 2000 reads per second for analogRead() and
> 2000 writes per second for analogWrite().
Note that most time is probably spend on I2C communication.
The auto-increment functionality is used in the analogRead4() function. The library only supports it for the mode 0 (plain ADC, no differential). The lastRead() function is needed to get access to the values. First tests shows it is 2.6 x faster than 4 individual reads.
analogRead4() needs investigation in the future for the other modi.
Interface
Generic
- PCF8591(const uint8_t address, TwoWire *wire = &Wire) constructor with I2C address, default is 0x48, optional set the WireN I2C bus.
- bool begin(uint8_t sda, uint8_t scl, uint8_t value = 0) set wire pins for ESP series.
Also set initial value for the DAC. Returns true if successful. - bool begin(uint8_t value = 0) Set initial value for the DAC. Returns true if successful.
- bool isConnected() test to see if chip can be reached.
ADC channels
The PCF8591 has four 8 bit ADC channels. Values = 0..255.
- void enableINCR() used in analogRead4(). Could become private in the future.
- void disableINCR() idem.
- bool isINCREnabled() idem.
- uint8_t analogRead(uint8_t channel, uint8_t mode = 0) read one of the 4 analogue ports.
Default mode is single ports. For comparator modes test datasheet. - uint8_t analogRead4() read all 4 channels in one call. Uses enableINCR() to do that efficiently. It is about 2.6 x faster than 4 individual analogRead(), although the latter allows for optimized timing per channel. Only 4x single ports mode supported for now, comparator modi needs investigation. Returns PCF8591_OK or an error code.
- uint8_t lastRead(uint8_t channel) get last read value from cache.
This cache is filled both by analogRead() and analogRead4(). See example sketch.
DAC channel
The PCF8591 has one 8 bit DAC. output value 0..255 == 0..Vref Volts (datasheet).
- void enableDAC() switch on the analogue output.
- void disableDAC() switch off the analogue output (high impedance). Sort of energy saving mode.
- bool isDACEnabled() check the modus operandi.
- bool analogWrite(uint8_t value = 0) writes a value 0..255 to the DAC. Check datasheet for voltage. Note, this is a real voltage not a PWM signal like analogWrite() on an UNO.
- uint8_t lastWrite() get last written value from cache.
Error codes
- int lastError() always check this value after a read / write to see if it was OK (== 0). After the read the error value is reset to OK.
To elaborate
| error code | Value | Notes |
|---|---|---|
| PCF8591_OK | 0x00 | |
| PCF8591_PIN_ERROR | 0x81 | |
| PCF8591_I2C_ERROR | 0x82 | |
| PCF8591_MODE_ERROR | 0x83 | |
| PCF8591_CHANNEL_ERROR | 0x84 | |
| PCF8591_ADDRESS_ERROR | 0x85 |
Operations
See examples.
Future
must
- improve documentation
should
- add / improve comparator modi support, datasheet (par.8.2 figure 4)
- int16_t readComparator10()
- int16_t readComparator30() - return type correct?
- int16_t readComparator31()
- int16_t readComparator32()
- set modi and read.
could
- analogRead4() needs investigation for the other modi.
- Does it work?
- Is it user understandable?
- good example