Arduino to Triac connection ..........

I have now got my solar divert system working finally after fitting a longer immersion heater! An 11" immersion heater dosn't have much effect in a 1.5m tall tank .....

It would be really useful to have an external indicator as a "repeater" for the Tric on/off signal LED as built into the Arduino board.

Looking at the diagram, the LED feed to the Opto isolator is a +5 connection and one direct into the chip, I'm assuming that the chip then sinks the current. I dont want to connect too heavy a load to the chip so can anyone suggest a suitable simple circuit that would allow me to control an additional LED so that I can see what's happening more easily.

I was thinking of a simple NPN transistor (BC108 family?) with the emitter connected to Ov, the base via a suitable resistor to the Arduino output and my chosen LED(S) into the collector via suitable resistors to a supply rail. I accept that this would only work if the Opto isolatoe was working - which is what I want.

Comments welcome - thanks - Rob


Robert Wall's picture

Re: Arduino to Triac connection ..........

Why not simply use a separate output and drive that at the same time in the software?

Otherwise, if you've got a 5 V supply, you can probably, if it's a red LED, wire the LEDs in series and adjust the current limiting resistor to suit. You'd need to do the sums on the worst-case conditions to find the optimum resistor value, but I'd guess it is 75 Ω as that's what I use with 3.3 V emonTx.  I need to put the driver i.c in the high side and the ATMega is active low; because it has a lower voltage drop to the 0 V rail when low than from the supply when high - check the data sheet if that doesn't immediately make sense.

calypso_rae's picture

Re: Arduino to Triac connection ..........

Yes, as Robert has said, the easiest approach is just to drive a spare digital pin on and off at the same time as the trigger.  Many of the Mk2 versions do this already, e.g. in Mk2_PV_Router_mini_3 :

         // first check the level in the energy bucket to determine whether the
          // triac should be fired or not at the next opportunity
          if (energyInBucket > (capacityOfEnergyBucket / 2))       
            nextStateOfTriac = ON;  // the external trigger device is active low
            digitalWrite(outputPinForLed, 1);  // active high
            nextStateOfTriac = OFF;
            digitalWrite(outputPinForLed, 0); 
          // then set the Arduino's output pin accordingly,
          digitalWrite(outputPinForTrigger, nextStateOfTriac);  
          // and clear the flag.
          triggerNeedsToBeArmed = false;       

Here, the LED is used in "active high" mode because it matches the Uno's on-board LED.  The trigger is "active low" because the Uno has slightly better drive characteristics in that mode.

richmc's picture

Re: Arduino to Triac connection ..........

If you want an indicator at the Arduino end just connect an LED (with a 200ohm resistor) between pin 13 and GND they are next to each other on the board and no programing is requied. if you want the LED remote i.e. by the triac if you use say CAT5 cable or telephone wire to wire it you will have spare cores to run from the arduino to the tricac remote position. If you just want to open your tank cupboard and have an indication then you can get a mains plate for the immersion with a neon on it,

Comment viewing options

Select your preferred way to display the comments and click "Save settings" to activate your changes.