Digital signals are explicitly made for noise resistance. The best solution is to use a separate amp for each thermocouple and multiplex the data connection between the amps and the microcontroller. The Arduino has 6 analog pins, which means we can monitor a maximum of 6 sensors. 74HC4067 DeMux For Arduino A multiplexer of this sort really just acts as a 16 to one 1 switch ArduSerie 83 Hi, in this post we're gonna talk about this 74HC4067 Fig 1. This is helpful in devices where there are only 1 or few analog pins. Arduino output to one74HC4067 INHIBIT, and to 180 ohm resistor, other side to transistor base transistor emitter to ground +5 to 5K resistor, other side to transistor collector, same junction goes INHIBIT on the second part. This module is used when you need to monitor multiple sensors or input devices on a single port. They’re dual latching relays so you can make connections to both wires at the same time, and it only takes a pulse of current to open or close them.Įven with those you’ll get some error from the wire between the relays and the thermocouple amplifier and the actual thermocouple wires. The CD74HC4067 is a 16-channel multiplexer. They’re the same kind used in my Keithley 6-1/2 digit bench multimeter, so their performance is pretty good. ICQUANZX 5 st 16CH analog digital multiplexer breakout board modul CD74HC4067 CMOS exakt modul : : Industriella verktyg & produkter. The third problem is that even small amounts of offset voltage through the switch can overwhelm the tiny voltage the thermocouple amplifier wants to measure.įor that kind of job, it’s better to use good quality relays like these: With arduino Uno with a multiplexor that is working flawless I am using following code const int muxSIG A0 const int muxS0 8 const. The second problem is that the free ends of the wires need to be at the same temperature for the thermocouple to work properly. So the first challenge for trying to use an analog switch with a thermocouple is that you have to switch both wires, not just one. A thermocouple amplifier measures that difference (which is usually in the microvolt range) and converts the reading to a temperature based on previously collected information about the Seebeck voltages of the two wires. The exact voltage depends on the material the wire is made of, so if you have two wires of different alloys connected at one end, and put the same temperature gradient across both, you’ll see the difference between their Seebeck voltages at the free ends. That acts like a resistance, and creates a voltage difference between the hot and cold ends. If one end of a long wire is hot and the other end is cold, the electrons have to slow down as they move from the hot end to the cold end. I have spent a lot of time trying to get my 74HC4067 to work with my Arduino Mega 2560 but I have been unable to find any answers so I am resorting to creating my own post in hopes I can solve my issues. Thermocouples operate on the Seebeck effect: the propagation speed for electrons in a cold piece of wire is slower than in a hot piece of wire. You should see all 16 signals printed or plotted.Getting thermocouples to work with analog switches is an iffy prospect. If you are using a 3-bit multiplexer, like the CD74HC4051, you can uncomment the code specific to this multiplexer, and use only three address pins.Ĭonnect some potentiometers or other analog sensors to the 16 inputs of the multiplexer, and open the serial monitor (CTRL+SHIFT+M) or the serial plotter (CTRL+SHIFT+L). Otherwise, just connect the enable pin to ground. Optionally you can connect the enable pin as well, this is useful if you want to use multiple multiplexers with the same address lines and the same analog input. I am able to control one 12-LED-string by using CD74HC4067 library. Testing a CD74HC4067 mux.thru the mux get different voltage readings than direct. I have a project for a Led clock where Ill have 12-LED-string to indicate Hours and other 12-LED-string to indicate 5-minute stretches. Dear, I am quite new at this staff and now I feel stuck for this issue. A0: CD74HC4067 signal pin ("common input/output") 2 CD74HC4067 Multiplexer with Arduino Uno.Boards: AVR, AVR USB, Nano Every, Nano 33 IoT, Nano 33 BLE, Pi Pico, Due, Teensy 3.x, ESP8266, ESP32 It prints the values of all 16 inputs of a multiplexers to the serial monitor. This is an example of the AnalogMultiplex class.
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