Hi all,
I’m using an Arduino Uno as an embedded controller. As usual, the project has grown, now I need additional digital pins to read two Oilmex Mod-TC thermocouple modules (uses the MAX 6675 chip).
The code seems to be assigning the MAX6675 CLK CS and DO to digital pins 4, 5, and 6 respectively.
But I only have 4 unused digital pins.
I’m sure (not positive) that that the ICSP header signals MISO = DO and SCK = CLK so shouldn’t I be able to fan out the ICSP header pins MISO and SCK signals to the two tc modules and then use only two pins for the CS?
If so how do I go about it? I’ve attached the library in case it is a way to assign the pins (I’m just guessing). Finally, I tried just moving the DO wire (assigned to pin 4?) to the MISO, but it don’t work
// this example is public domain. enjoy!
// www.ladyada.net/learn/sensors/thermocouple
#include "max6675.h"
int thermoDO = 4;
int thermoCS = 5;
int thermoCLK = 6;
MAX6675 thermocouple(thermoCLK, thermoCS, thermoDO);
int vccPin = 3;
int gndPin = 2;
void setup() {
Serial.begin(9600);
// use Arduino pins
pinMode(vccPin, OUTPUT); digitalWrite(vccPin, HIGH);
pinMode(gndPin, OUTPUT); digitalWrite(gndPin, LOW);
Serial.println("MAX6675 test");
// wait for MAX chip to stabilize
delay(500);
}
void loop() {
// basic readout test, just print the current temp
Serial.print("C = ");
Serial.println(thermocouple.readCelsius());
Serial.print("F = ");
Serial.println(thermocouple.readFahrenheit());
delay(1000);
Unless you are using SPI in theory those pins are available for anything.
But I only have 4 unused digital pins.
The SPI header on the Uno is directly connected to pins D11/D12/D13 which are the SPI pins. The header does not give you "extra" pins. (The other three are +5V/Gnd/Reset).
It looks like the device only needs 3 pins apart from power and Gnd, so aren't 4 pins plenty?
I hope to accommodate 2 TC modules so it would take 6 pins. My thought was to fan out the MISO and clk to the modules and then use only 2 digital pins for CS (SS). I think CS has to toggle to read the serial. But I don't know how to code that. I'm new to both C and Arduino. Although I have had programming experience a while ago with VB.Net. I'm still learning how to use Libraries and classes. I've been studying these in the Arduino site. I have some spare AI pins so I can use those as output using pinMode
But again, I am not sure how to change the pins assigned in the example (in my original post).
Still trying
Gene
I count only 4 pins (as suggested by Nick Gammon) ...
EDIT:
You may need a pullup resistor on MISO (i.e. 2.2K - 10K).
You may need to insert a small delay after CSn goes high to allow 1 SCK cycle for SOn to go tristate (high impedance) before the next device is enabled.
I have been looking around to find an example of coding more than one instance of a constructor.
(in other words - creating more than one object of a class?) (not even sure how to state the problem!)
So I want to read 2 TCs the example given with the library works great. but when I try to read 2 not so good. this is one try...
// this example is public domain. enjoy!
// www.ladyada.net/learn/sensors/thermocouple
#include "max6675.h"
int thermoDO = 4;
int thermoCS = 5;
int thermo2CS = 6;
int thermoCLK = 7;
MAX6675 thermocouple(thermoCLK, thermoCS, thermoDO);
MAX6675 thermocouple2(thermoCLK, thermo2CS, thermoDO);
void setup() {
Serial.begin(9600);
Serial.println("MAX6675 test");
// wait for MAX chip to stabilize
delay(500);
}
void loop() {
// basic readout test, just print the current temp
Serial.print("C1 = ");
Serial.println(thermocouple.readCelsius());
Serial.print("C2 = ");
Serial.println(thermocouple2.readCelsius());
delay(1000);
}
there is a lot more to my application - this just focuses on 2 TC modules.
I don't get how to use the constructor so I can share 2 of the 3 pins required for each TC modules
Just for closure This Issue was a hardware wiring issue the header has inconsistent configuration (somehow?) My original code ran two modules using only 4 pins. dlloyd's graphic was great
Regards
Gene
