Arduino – MCP42010 controlling several digital potentiometers in cascade

Arduino – MCP42010 – Example of controlling several digital potentiometers

After the example Arduino – control and test digital potentiometer MCP42010 on breadboard and the graphic variant Node Red – Arduino – control digital potentiometer MCP42010 I tested the control of 2 digital potentiometers MCP42010 cascaded.



Control of the two MCP42010

The control of the primary MCP42010 is described in detail in Arduino – Control and Test Digital Potentiometer MCP42010 on breadboard.
Write in potentiometer 1 -> B00010001 and in potentiometer 2 -> B00010010
The value that the selected potentiometer should set is transmitted as the second byte.

To reach the second MCP42010, 4 bytes have to be sent instead of 2 bytes for a single one.
With three MCP42010 6 bytes are required, with four 8 bytes and so on.
In order to control a potentiometer of the second MCP42010 directly without changing the contents of the first chip, two more bytes with the value 0 are sent.
See also the picture on the left from the data sheet.

Write in potentiometer 3 -> B00010001 value B00000000 B00000000
Write in potentiometer 4 -> B00010010 value B00000000 B00000000

The whole thing has to be read from right to left.
4 bytes are written, or better shifted into it.
The first two bytes (from the left) are shifted from the following two bytes into the second MCP42010.
Two bytes with ‘zero’ arrive in the first MCP42010, i.e. no changes to the values in the 1st chip.

Here is a minimal example of how the value 127 is loaded into potentiometer 1 (Pot0) of the second MCP42010.

Node Red

Arduino – Node Red – MCP42010 control the digital potentiometer

Arduino – Node Red – MCP42010 – Sample control of the digital potentiometer

In the article Arduino – control and test digital potentiometer MCP42010 on a breadboard I showed how the MCP42010 can be controlled via the serial monitor of the Arduino IDE.
Now I want to do this more comfortably.
The operation has to take place from the browser, should look visually very appealing and it must also be possible with the smartphone.

Why with Node Red?

Node Red is included in the standard installation of the Raspberry Pi, free and intuitive to use.
By the possibility of clicking together the flow by drag and drop together, one comes very quickly to a good result.
For prototypes and also IOT applications this is a really great thing.
Where light is, is also shadow: Node Red consumes quite a lot of resources.
Nevertheless, the Raspberry Pi 2 does well and the performance with the Pi 3 should still much better.

Required functions of the flow

The flow is supposed to take over the entries, which I have done by hand in the Arduino – control and test digital potentiometer MCP42010 on a breadboard.
The flow should represent the return values in a Gauge Chart.

data input:
1:Value between 0-255
-> sets potentiometer1 to the value and returns the voltage to A0
2:Value between 0-255
-> sets potentiometer2 to the value and returns the voltage to A1

The Flow

  • copy the following flow and insert it under menu (top right) -> Import – Clipboard
[{"id":"ebf0e947.110038","type":"ui_slider","z":"8ec3bd3.cce4dc","tab":"147200e2.b8e19f","name":"Slider","topic":"","group":"Pot1","order":1,"min":0,"max":"255","x":225.5,"y":125,"wires":[["25bd2695.9acaf2"]]},{"id":"b755b484.2bd75","type":"ui_text","z":"8ec3bd3.cce4dc","tab":"147200e2.b8e19f","name":"Wert","group":"Pot1","order":1,"format":"{{msg.payload}}","x":636.5,"y":102,"wires":[]},{"id":"ed9f01b2.dfae38","type":"ui_gauge","z":"8ec3bd3.cce4dc","tab":"147200e2.b8e19f","name":"Spannung in V an A0","group":"Pot1","order":1,"format":"{{value}}","min":0,"max":"5","x":681.5,"y":322,"wires":[]},{"id":"25bd2695.9acaf2","type":"function","z":"8ec3bd3.cce4dc","name":"Value to Command","func":"var msg1 = { payload:\"1:\" + msg.payload +\"\\n\"};\nreturn [msg, msg1];","outputs":"2","noerr":0,"x":440.5,"y":125,"wires":[["b755b484.2bd75"],["134514.6c0042ed"]]},{"id":"134514.6c0042ed","type":"serial out","z":"8ec3bd3.cce4dc","name":"/dev/ttyUSB0","serial":"d535ccdc.123838","x":658.5,"y":148,"wires":[]},{"id":"13db30d1.da3c67","type":"serial in","z":"8ec3bd3.cce4dc","name":"/dev/ttyUSB0","serial":"43aa993f.185738","x":186.5,"y":345,"wires":[["f39416bc.0495"]]},{"id":"f39416bc.0495","type":"function","z":"8ec3bd3.cce4dc","name":"Response to value","func":"//find A0 or A1\nvar value;\nif (msg.payload.indexOf(\"A0\") != -1) {\n    value = msg.payload.split(\"A0: \");\n    value = value[1].replace(\" Volt\", \"\");\n    msg.payload = value;\n    return [msg, null];\n} else {\n    value = msg.payload.split(\"A1: \");\n    value = value[1].replace(\" Volt\", \"\");\n    msg.payload = value;\n    return [null , msg];\n}","outputs":"2","noerr":0,"x":431.5,"y":345,"wires":[["ed9f01b2.dfae38"],["ddbfff6.2bdb3"]]},{"id":"8a48ef7d.33ba9","type":"ui_slider","z":"8ec3bd3.cce4dc","tab":"147200e2.b8e19f","name":"Slider","topic":"","group":"Pot2","order":1,"min":0,"max":"255","x":224,"y":227,"wires":[["127d632d.c0419d"]]},{"id":"5a58be54.e6b8d8","type":"ui_text","z":"8ec3bd3.cce4dc","tab":"147200e2.b8e19f","name":"Wert","group":"Pot2","order":1,"format":"{{msg.payload}}","x":635,"y":204,"wires":[]},{"id":"127d632d.c0419d","type":"function","z":"8ec3bd3.cce4dc","name":"Value to Command","func":"var msg1 = { payload:\"2:\" + msg.payload +\"\\n\"};\nreturn [msg, msg1];","outputs":"2","noerr":0,"x":439,"y":227,"wires":[["5a58be54.e6b8d8"],["ee1b0407.9fbca"]]},{"id":"ee1b0407.9fbca","type":"serial out","z":"8ec3bd3.cce4dc","name":"/dev/ttyUSB0","serial":"43aa993f.185738","x":657,"y":250,"wires":[]},{"id":"ddbfff6.2bdb3","type":"ui_gauge","z":"8ec3bd3.cce4dc","tab":"147200e2.b8e19f","name":"Spannung in V an A1","group":"Pot2","order":1,"format":"{{value}}","min":0,"max":"5","x":681,"y":370,"wires":[]},{"id":"147200e2.b8e19f","type":"ui_tab","z":"","name":"Test MCP42010","icon":"dashboard","order":"1"},{"id":"d535ccdc.123838","type":"serial-port","z":"","serialport":"/dev/ttyUSB0","serialbaud":"9600","databits":"8","parity":"none","stopbits":"1","newline":"\\n","bin":"false","out":"char","addchar":false},{"id":"43aa993f.185738","type":"serial-port","z":"","serialport":"/dev/ttyUSB0","serialbaud":"9600","databits":"8","parity":"none","stopbits":"1","newline":"\\n","bin":"false","out":"char","addchar":false}]

Video Controlling MCP42010 with Node Red


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