Page 1 of 1
Transferring a Byte via SPI
Posted: 23 Oct 2021, 22:54
by Roland_60
Hi!
I need to control a Digital Potentiometer (MCP 4151-103E/P) via the SPI interface of the nodeMCU. The value is received from the host via MQTT.
The digital potentiometer will substitute a manual potentiometer in the controller of my heating system.
I use the same nodeMCU to read some temperatures using DS18b20 and transfer those via MQTT as well.
I study already for a while the documentation. I found that SPI is somehow supported. However, I cannot find out how I could use it for this purpose. I need to transfer only one Byte via SPI to this device and the value will change only few times a day.
Could anybody give me a hint how to do?
Best regards,
Roland
Re: Transferring a Byte via SPI
Posted: 23 Oct 2021, 23:00
by TD-er
Currently the only way how SPI is used in ESPEasy is via plugins for specific hardware.
So the best way here would be to write a very basic plugin to support your potentiometer chip and accept commands for it (implemented in PLUGIN_WRITE call in the plugin)
The reason why I think it should be a plugin is that you need to select something else like a CS line too and you definately don't want to add a command that would write just anything to the SPI bus as it may cause a lot of havoc.
Re: Transferring a Byte via SPI
Posted: 23 Oct 2021, 23:25
by Roland_60
Thank you for the swift answer.
I found a documentation how to add a plugin to ESPEasy and I had a look to the plugins in the src folder. Which of those plugins would be best as a template for my project?
Re: Transferring a Byte via SPI
Posted: 23 Oct 2021, 23:31
by TD-er
I would go for the smallest, as you simply won't have to do a lot in the plugin.
P006 BMP085 is a nice small one to start with to see how quickly you can get it to compile with your own changes (e.g. start with renaming the plugin and assigning a new plugin ID to it for starters)
To see one of the simple SPI plugins (not using a lot of GPIO pins) see where DEVICE_TYPE_SPI is used, like P039
Re: Transferring a Byte via SPI
Posted: 28 Sep 2022, 19:40
by ankan
Roland_60: How did it go? Did you manage to implement your digital potentiometer with espeasy?
Re: Transferring a Byte via SPI
Posted: 15 Oct 2022, 17:56
by Roland_60
Hi!
Yes, it worked. However, I was working on this a year ago and I hardly remember how I made it and the project is not yet finished. The target was to make my domestic heating system smarter replacing the manual control with this digi-poti. Finally, I had to give other issues a priority and the project is still stuck. But winter is coming! I will resume to work on this. (Although my old oil-fired heating system is due for replacement)
What I have by now is the following:
I used, as recommended the P006 BMP085 as template. I did create a P116 and did list it in define_plugin_sets.h.
Working with the Arduino IDE I used the features provided in this environment for the SPI communication with the module.
Init module and communication:
Code: Select all
case PLUGIN_INIT:
{
SPI.begin();
pinMode(CHIPSELECT, OUTPUT);
wiper = 0.5;
success = true;
break;
}
Writing a value if ESP Easy receives the command mcp41xx_digipoti followed by a real number between 0 and 1
Code: Select all
case PLUGIN_WRITE:
{
String command = parseString(string, 1, ':');
if (command == "mcp41xx_digipoti") {
String cmdValue = parseString(string, 2, ':');
char str[20];
wiper = atof(&cmdValue[0]);
if (wiper > 1) {
wiper = 1;
}
if (wiper < 0) {
wiper = 0;
}
uint8_t setCValue = (uint8_t) (255 * wiper);
digitalWrite(CHIPSELECT, LOW);
delay(100);
SPI.transfer(B00000000); //write cmd
SPI.transfer(setCValue); //write value
delay(100);
digitalWrite(CHIPSELECT, HIGH);
} //command == "mcp41xx_digipoti"
UserVar[event->BaseVarIndex] = wiper;
success = true;
break;
} // case PLUGIN_WRITE:
}
Sorry for the late answer.
Roland
Re: Transferring a Byte via SPI
Posted: 15 Oct 2022, 18:45
by ankan
@Roland_60 thanks for your replay.
I have it now working in ESPEasy with a MCP41010 that is controlling my indoor termostat on my heatpump.
For someone who knows ESPEasy l guess it is quite easy to develop a ESPEasy component but I just created a custom spi device.