Multiple temperature sensors on a emonPi?

hockeyshooter · 24 January 2017 09:54

Just want to check that it is still possible to connect multiple temperature sensors, via an RJ45 Multi Breakout board, to an emon Pi, rather than having to use a Tx as well?

I was sure the earlier Pis we bought had an internal sensor but those with built-in wifi (presumably based on the Pi3) don’t appear to have that any more - is that true or am I just going nuts?

Robert.Wall · 24 January 2017 17:27

As far as I know, the emon part of the emonPi has never had an internal temperature sensor, it’s only the emonTH and emonGLCD that have had that. The emonPi and emonTx can both accept one or several temperature sensors via the RJ45 socket, and the emonTx via the terminal block also. Caution: use the correct RJ45 in the case of the emonPi.

glyn.hudson · 24 January 2017 21:40

Yes it is. The default firmware on emonPi / emonTx allows up to 6x ds18b20 temperature sensors to be connected to the RJ45 input.

All raspberry Pi’s have got a SOIC (CPU) temperature sensor, I’m not sure if it has another temperature sensor but it would be useless for ambient temperature monitoring since the whole Pi PCB gets quite warm inside an enclosure.

Bill.Thomson · 25 January 2017 02:27

The enclosure does indeed make it useless, but It would be useless even if the Pi wasn’t in an enclosure.
Soon after the CPU load rises to anything above idle, the sensor will detect a temperature increase.

If the ambient temperature is less than the CPU idle temp…

hockeyshooter · 25 January 2017 14:16

The older Pi I’m currently setting up shows Temp 1 and Temp 2 on its internal display - Temp 1 appears to reflect the probe I have connected to the RJ45 socket. I understand what you’re saying about an internal sensor being useless.

pb66 · 25 January 2017 15:32

Although the emonPi display is only configured to display the first 2 temp sensors

github.com

openenergymonitor/emonpi/blob/master/lcd/emonPiLCD.py#L382

    
      
          logger.addHandler(loghandler)
          logger.setLevel(logging.INFO)
          
          
logger.info("Starting emonPiLCD V" + version)
          
          
# Now check the LCD and initialise the object
          # Scan I2C bus for LCD I2C addresses as defined in led_i2c, we have a
          # couple of models of LCD which have different addreses that are shipped
          # with emonPi. First I2C device to match address is used.
          global lcd
          for i2c_address in lcd_i2c:
              try:
                  lcd = lcddriver.lcd(int(i2c_address, 16))
                  lcd.backlight = 1
              except OSError:
                  # No LCD at this address, try the next...
                  continue
              print("I2C LCD DETECTED Ox%s" % i2c_address)
              logger.info("I2C LCD DETECTED 0x%s" % i2c_address)
              # identify device as emonpi
              r.set("describe", "emonpi")

github.com

openenergymonitor/emonpi/blob/master/lcd/emonPiLCD.py#L391

    
      
          global lcd
          for i2c_address in lcd_i2c:
              try:
                  lcd = lcddriver.lcd(int(i2c_address, 16))
                  lcd.backlight = 1
              except OSError:
                  # No LCD at this address, try the next...
                  continue
              print("I2C LCD DETECTED Ox%s" % i2c_address)
              logger.info("I2C LCD DETECTED 0x%s" % i2c_address)
              # identify device as emonpi
              r.set("describe", "emonpi")
              break
          else:  # no break
              print("I2C LCD NOT DETECTED on either 0x" + str(lcd_i2c) + " ...exiting LCD script")
              logger.error("I2C LCD NOT DETECTED on either 0x" + str(lcd_i2c) + " ...exiting LCD script")
              # identify device as emonbase
              r.set("describe", "emonbase")
              sys.exit(0)
          
          
# This is a row-major bitmap of a character.

the firmware and the subsequent payload is for 6 temp sensors

github.com

openenergymonitor/emonpi/blob/master/firmware/src/src.ino#L43

    
      
          Change Log:
          https://github.com/openenergymonitor/emonpi/blob/master/Atmega328/emonPi_RFM69CW_RF12Demo_DiscreteSampling/compiled/CHANGE%20LOG.md
          
          
emonhub.conf node decoder:
          
          
[[5]]
              nodename = emonPi
              firmware = emonPi_RFM69CW_RF12Demo_DiscreteSampling.ino
              hardware = emonpi
              [[[rx]]]
                  names = power1,power2,power1_plus_power2,Vrms,T1,T2,T3,T4,T5,T6,pulseCount
                  datacodes = h, h, h, h, h, h, h, h, h, h, L
                  scales = 1,1,1,0.01,0.1,0.1,0.1,0.1,0.1,0.1,1
                  units = W,W,W,V,C,C,C,C,C,C,p
          
          
*/
          
          
#define emonTxV3                                                      // Tell emonLib this is the emonPi V3 - don't read Vcc assume Vcc = 3.3V as is always the case on emonPi eliates bandgap error and need for calibration http://harizanov.com/2013/09/thoughts-on-avr-adc-accuracy/
          #define RF69_COMPAT 1                                                 // Set to 1 if using RFM69CW or 0 is using RFM12B
          
          
#include <JeeLib.h>                                                   // https://github.com/openenergymonitor/jeelib

hockeyshooter · 25 January 2017 15:55

So data from up to 6 sensors would still be transmitted - without me having to change any code?

glyn.hudson · 25 January 2017 16:11

Correct, the emonTx and emonPi both support up to six sensors without any changes in firmware. More sensors can be added if the firmware is modified, we played it safe setting a 6 sensor limit. Only data from the first two sensors connected to an emonPi will show on the LCD. Data from all the sensors will be posted to Emoncms. The emonPi LCD will display the total number of sensors detected at power-up.

hockeyshooter · 25 January 2017 16:12

This is good news. At the moment I think three will be enough.