Hello everyone,
with a arduino "one" according to the temperature that I read by a sensor LM335 st I manage the speed of my fan of the greenhouse.
Arduino fails if the fan remains stopped. how to make sure that if Arduino fails the fan parts 100%
Hold on a minute. You want the fan to be on full power if the Arduino fails somehow? That should be pretty easy. How are you controlling the fan? What motor driver are you using?
with a arduino "one"
No it is called an Arduino Uno, you don't translate the Uno bit.
how to make sure that if Arduino fails the fan parts 100%
The simplest way is to use a relay to switch the fan and use the common and normally closed contacts. Then the Arduino activates the relay to turn the fan off. Then when the relay is turned off either through the program or Arduino failure the fan turns on.
Or a MOSFET with a pullup resistor. (I am not a MOSFET expert, ask someone who is.)
Isaac96:
Or a MOSFET with a pullup resistor.
Yes but pull up to what. If the Arduino failed then there probably would be nothing to pull up to. You can't pull up to +12V as then the Arduino would see 12V on it's output and fry it. Therefore you would have to have a transistor to isolate it so it is more complex than just that.
You could have a diode between the Arduino output and the pullup resistor. Or you could use a P-type MOSFET. (I think that is right.)
You could have a diode between the Arduino output and the pullup resistor.
To do what? It would not protect the Arduino output on way round and the other way round it would not let you turn off the fan.
Or you could use a P-type MOSFET.
still the same problem of generating the 12V signal to turn it off.
Sorry, I meant between the Arduino pin and the gate of the MOSFET.
Draw out what you are thinking of because I can't picture anything that would work.
I mean like in the picture I attached.
The fan have 3 wires. Two wires for power and a wire for a control pwm signal. A caracterist of the fan is that when the control signal is high or disconnected the speed of the fan is 100%. I would like that when Arduino fails the speed of my fan has to be 100%. How connect Arduino pwm pin with the control wire of fan?
Isaac96:
I mean like in the picture I attached.
If that is a P- channel FET then you can never turn it off the diode stops you. If it is an n- channel FET then you can never turn it off for the same reasion.
cchechio:
The fan have 3 wires. Two wires for power and a wire for a control pwm signal. A caracterist of the fan is that when the control signal is high or disconnected the speed of the fan is 100%. I would like that when Arduino fails the speed of my fan has to be 100%. How connect Arduino pwm pin with the control wire of fan?
So now you tell us!!
What voltage level are we talking about for this signal 5V or the full fan voltage?
the fan is powered separately.
the voltage level of pwm signal is between 0V and 5V
That is not at all easy. This is because anything connected directly to the Arduino will be pulled to ground when the arduino fails and yet you need to be able to connect it to ground to have the off part of the PWM. You could try connecting the fan control through a seriese capacitor. My only worry about that is the negitave voltage spikes it creates might damage the control circuit in the fan.
Just had another thought, connect the PWM to the fan through a relay, then control the relay from the Arduino. If the Arduino fails then the relay opens and disconnects the PWM control.
Grumpy_Mike using a relay, for all the life of arduino the relay is closed.
Not sure what you mean by that.
The othe thought is to have a potential divider on the fan's supply to give you a 5V signal which you attach to the control signal. Then you put the output transistor of an opto isolator across the bottom resistor and drive the input of the opto isolator from the Arduino.
Why? It will not work the way you want. If the Arduino fails then the fan will not run.
what is the correct circuit?