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


Arduino MCP42010 – control and test the digital potentiometer

Arduino MCP42010 – test on a breadboard

There are many instructions to control digital potentiometers with an Arduino. The search for the MCP42010, was very promising, but led to success only after several attempts. Many web pages and foren entries discuss the topic, but in the end they do not come to a working solution.

The idea is to switch the two digital 10 kilohms potentiometers at the ends between 5 volts and ground and place the center of each potentiometer on an individual analog input.
Depending on what now for a resistor controlled, the voltage at the analog inputs will rise or fall. And this can be evaluated.

I describe how I proceeded.

I’ve been used an Arduino Nano replica, which is already available for a little more than 3.50 Euros, and a digital potentiometer MCP42010 (data sheet), which I ordered for about 2 euros at
I have also tested the design with a Arduino Uno and the same IO pins. Successful :-)

As shown in the following Fritzing image and the Eagle circuit diagram, I have wired as follows.
Pin relation MCP42010MCP42010:
Pin 1 -> D10 Arduino, Pin2 -> D13 Arduino, Pin3 -> D11 Arduino, Pin4 -> GND, Pin5 -> GND, Pin6 -> A1 -> Arduino, Pin7 -> +5V, Pin8 -> + 5V, Pin9 -> A0 Arduino, Pin10 -> GND, Pin11 -> +5V, Pin12 -> 5V, Pin13 – free, Pin14 -> 5V

Arduino: In addition to the connections at MCP42010, I had to connect only 5 Volt and ground at the Arduino to supply them with power.

Control of the MCP42010

MCP42010 datasheet excerptAs shown in the data sheet on page 18, CS (PIN 10) must be set to Low for the duration of the transmission.
2 bytes are sent for transmission.
First, a control byte, specifying the operation (write) and the pot (the desired one of the two potentiometers).
Write to potentiometer 1 -> B00010001 and to potentiometer 2 -> B00010010
The second byte is the value that the selected potentiometer should take up.
Here is a minimal example, as in the potentiometer 1 (Pot0) the value 127, thus approximate middle position is loaded.

//minimal Example to set the Pot0 of a MCP42010 to the value 127 
void setup() {
  // take the CS pin low to select the chip:
  //  send in the address and value via SPI:
  // write out the value 127
  // take the CS pin high to de-select the chip:
void loop() {

The program for ‘comfortable’ control of the 2 potentiometers of the MCP42010

The operation is very simple, as was already seen in the video above. I pass values to the digital potentiometer and evaluate the resulting voltage at the analog inputs A0 and A1.
For the data input and output I use the serial monitor of the Arduino IDE.

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
s -> returns values for both potentiometers and the voltages at the Pins A0 and A1

// inslude the SPI library:
// set pin 10 as the slave select for the digital pot:
const int slave_Select_Pin  = 10;
const int analogInPin0      = A0; 
const int analogInPin1      = A1; 
String    inputString       = "";         // a string to hold incoming data
boolean   stringComplete    = false;      // whether the string is complete
int       level1            = 0;
int       level2            = 0;
void setup() {
     // set the slaveSelectPin as an output:
     pinMode (slave_Select_Pin, OUTPUT);
     // initialize SPI:
     MSP42010PotWrite(slave_Select_Pin, B00010001, level1);
     MSP42010PotWrite(slave_Select_Pin, B00010010, level2);
void loop() {
  if (stringComplete) {
    //check ob R1:
    if (inputString.substring(0, 2) == "1:") {
      level1 = inputString.substring(2).toInt();
      MSP42010PotWrite(slave_Select_Pin, B00010001, level1);     
      printValues(level1, analogInPin0);
    //check ob R2:
    if (inputString.substring(0, 2) == "2:") {
      level2 = inputString.substring(2).toInt();
      MSP42010PotWrite(slave_Select_Pin, B00010010, level2); //Datasheet Page 18
      printValues(level2, analogInPin1);
    //check ob s
    if (inputString.substring(0, 1) == "s") {
      printValues(level1, analogInPin0);
      printValues(level2, analogInPin1);
    // clear the string:
    inputString = "";
    stringComplete = false;
void MSP42010PotWrite(int slaveSelectPin, byte address, int value) {
     // take the SS pin low to select the chip:
     //  send in the address and value via SPI:
     // take the SS pin high to de-select the chip:
void printValues(int level, int aPin) {
      int pot = 0;
      if (aPin == 15) {
        pot = 1;
      Serial.print("level Pot");
      Serial.print(": ");
      Serial.print(" Spannung an A");
      Serial.print(": ");
      double sl = analogRead(aPin);
      sl = sl * 5 / 1024; 
      Serial.println(" Volt");  
  SerialEvent occurs whenever a new data comes in the
 hardware serial RX.  This routine is run between each
 time loop() runs, so using delay inside loop can delay
 response.  Multiple bytes of data may be available.
void serialEvent() {
  while (Serial.available()) {
    // get the new byte:
    char inChar = (char);
    // add it to the inputString:
    // if the incoming character is a newline, set a flag
    // so the main loop can do something about it:
    if (inChar == '\n') {
      stringComplete = true;
    } else {
      inputString += inChar;

Papst ebm G1G133-DE19-15* fan speed measuring / controlling with Arduino and Raspberry Pi

On ebay are offered used fan with DC motors from 13 euro, which with up to air flow: 225 m³ per hour with a maximum of 45 watts have very good performance values.
For me it was important that it is possible to regulate the speed of the fan, because I don’t always need full power.

In the reviews of the product below in the auction, it was announced that the speed of the motor can be controlled by PWM.
This data sheet of an almost identical fan shows on page 4 that it is possible to control the speed via a PWM signal. With my fan this doesn’t work.

After many attempts to create a PWM signal and to pick up a speed pulse, I decided to take the fan apart.

Inside it is not a normal DC motor, that is more a microcontroller-controlled high-tech product. I am sure that the circuitry would allow speed control even if for that the internal fan microcontroller’s code would have to be adapted.

continuing on the following pages:


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