MCP4726 - 12 Bit I2C DAC Driver for ESP8266 CBDB Board - Part 1

    At least from the zillions of request for a DAC Driver implementation example that I received in the latest weeks, this is the long awaited topic: ESP8266 Modules and Voltage Output Digital-to-Analog Converter control!

    For our project we will use Microchip MCP4726, a Voltage Output Digital-to-Analog Converter (DAC) with EEPROM and I2C™ Interface.

    As you will see, despite the fact that is a tiny one, it's a very versatile chip with a great price/capabilities ratio. If you take a look on Digikey for example it can be found at around 1.15$!

Features:

• Output Voltage Resolutions:
 - 12-bit: MCP4726
 - 10-bit: MCP4716
 - 8-bit: MCP4706

• Rail-to-Rail Output

• Fast Settling Time of 6 μs (typical)

• DAC Voltage Reference Options:
- VDD
- VREF Pin

   The VREF pin or the device VDD can be selected as the DAC’s reference voltage. When VDD is selected, VDD is connected internally to the DAC reference circuit.  When the VREF pin is used, the user can select the output buffer’s gain to 1 or 2. When the gain is 2, the VREF pin voltage should be limited to a maximum of VDD/2.

  That means that it has also an internal reference and if you don't need very high accuracy or you have a very stable power supply for MCP4726 DAC, you don't need to use an external expensive Voltage Reference to make it working decent! If you are looking in the basement after boson Higgs cousin then this 1.15$ DAC is not what are you looking for :)

• Output Gain Options:
- Unity (1x)
- 2x, only when VREF pin is used as voltage
source

• Nonvolatile Memory (EEPROM):
- Auto Recall of Saved DAC register setting
- Auto Recall of Saved Device Configuration
(Voltage Reference, Gain, Power-Down)

• Power-Down modes:
- Disconnects output buffer
- Selection of VOUT pull-down resistors
(640 kΩ, 125 kΩ, or 1 kΩ)

• Low-Power Consumption:
- Normal Operation: 210 μA typical
- Power-Down Operation: 60 nA typical
(PD1:PD0 = 11)

• Single-Supply Operation: 2.7V to 5.5V

• I2C™ Interface:
- Eight Available Addresses - Factory hardcoded !! - if you need more than one to run in your project be carefully when ordering!!
- Standard (100 kbps), Fast (400 kbps), and
High-Speed (3.4 Mbps) modes

• Small 6-lead SOT-23 and DFN (2x2) Packages
• Extended Temperature Range: -40°C to +125°C

For more details, please see MCP4726 Datasheet

   Don't be scared by the SOT-23 package used, with a small SOT-23 to DIP adapter will fit great in our CBDB extension slots so it will not matter at all. Actually is even more manageable than the MCP9808 Temperature sensor MSOP-8 package used before

What we will need:

• CBDB Board
• USB adapter (take a look on Part 1 for details how to connect them together)
• MCP4726 Module from above
• LED module (if you want maybe a LED ticker)

CBDB with MCP4726 DAC and MCP9808 Temperature Modules

    Connection between the modules is pretty simple as both are I2C chip modules. Each of them is connected at +3V, GND and toghether on I2C bus using SDA and SCL lines. I will suggest also to do proper decoupling for MCP4726 Power and Vout pins (see picture above).

MCP4726 DAC Module connections

    Please remember that all released software examples are provided under MIT Licence, if no other specific options stated. I was asked about, so this is the reason of this declaration. Some people looks more interested in legal stuff than wide access to information. So, if you find on this website anything useful and you want to contribute, please send your comments or even a  donation. OR virtual beer. OR whaterver. OR nothing. Your choice.
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The MIT License (MIT)
 
Copyright (c) 2015       
esp8266-projects.com
 
Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions: The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.
 
THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
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  For programming and uploading the driver and the software we will continue to use the LuaUploader as before.

Driver implementation.
 
As MCP4726 has a I2C compatible compatible interface, building a driver for it it's a pretty straigh forward process:
1. Init I2C bus/interface
     
          dev_addr = 0x60,
          init = function (self, sda, scl)
                   self.id = 0
           i2c.setup(self.id, sda, scl, i2c.SLOW)
          end
 
  2. Write Volatile DAC Register Function.

          write_dac = function (self, voltage) 
               self.dev_addr = 0x60
               self.reg_addr = 0x40

               volt=(4096*voltage)/3.27 -- tweak the value for your VREF value
               print("Voltage Steps:" .. string.format("%d",volt))  --debug

               msb = bit.rshift(volt, 8)
               print("MSB:" .. string.format("%d",msb))              --debug

               lsb = volt-bit.lshift(msb,8)
               print("LSB:" .. string.format("%d",lsb))              --debug

               i2c.start(self.id)
               i2c.address(self.id, self.dev_addr ,i2c.TRANSMITTER)
               --i2c.write(self.id,self.reg_addr)
               i2c.write(self.id,msb)
               i2c.write(self.id,lsb)
               i2c.stop(self.id)
          end

For testing, just save the code on ESP as 'mcp4726.lua', restart ESP and run:

          require('mcp4726')
          sda=2 --GPIO4
          scl=1 --GPIO5
          mcp4726:init(sda, scl)
          mcp4726:write_dac(1.5)

Uploading Driver on ESP module

  If all OK, if you measure the DAC output (see picture above for connections) you will find the programmed voltage. 

MCP4726 DAC output voltage set

   
Youtube MCP4726 DAC Driver Test Video :





That's all for today, thank you for your great feedback and looking forward for your suggestions!