I have a large AC fan that I currently control with a SCR based regulator:
can I de-solder the pot and control this directly with the Arduino outputs?
what other things will I need to be considering, if any?
I don't HAVE to use this SCR regulator, but it seems to be working fine with the motor now - so was trying to keep it simple - if there is a better way, I would be interested...
I doubt that the pot can be easily replaced in a dimmer circuit. Eventually you can replace it by an LDR, and illuminate it with a PWM controlled LED.
Details depend on the exact circuit diagram - do you have one?
Some thing like:
can I de-solder the pot and control this directly with the Arduino outputs?
No! The Arudino (and yourself) needs to be electrically isolated from the power line voltage. (An LDR is one way of doing that.)
Typically, you use an opto-isolator that's specially designed for a TRIAC (or SCR). You also need a phase detection (or zero-crossing) circuit because the TRIAC (or SCR) trigger needs to be synchronized with the AC power frequency. Of course, the phase detection circuit must also be isolated.
Look-up "Phase controlled dimmer circuit".
And I'll bet that's a TRIAC, not an SCR.
thanks all!
DrDiettrich:
I doubt that the pot can be easily replaced in a dimmer circuit. Eventually you can replace it by an LDR, and illuminate it with a PWM controlled LED.
so I can replace the pot on that dimmer with an LDR?
then use PWM output from Arduino to change the 'brightness' of an LED, that will then change the resistance in the 220v circuit?
i have found a 500k LDR (to match the existing pot) that is rated for 400v (e.g. VT43N3) - but these only have two legs? will this work in the dimmer?
so if i understand correctly - i would need to work out how fast/slow to flash the LED and that will change the dimmer output in the range i want?
DVDdoug:
And I'll bet that's a TRIAC, not an SCR.
(i just checked the transistor - it's a 'BTA20' - a snubberless TRIAC - your bet pays!!!)
not sure how often you change the speed, but you could put a servo on the pot. just turn the pot with the servo
speed will be constantly varied - (based on inputs from a pair of DHT22's)
(i am actually surprised that an often cited Arduino solution to controlling a variable resistor is a mechanical "put a servo on it" solution?)
so is this the LDR/LED solution in a nutshell?
seems simple enough!
Wareemba:
so I can replace the pot on that dimmer with an LDR?then use PWM output from Arduino to change the 'brightness' of an LED, that will then change the resistance in the 220v circuit?
Right. But see below for using PWM.
i have found a 500k LDR (to match the existing pot) that is rated for 400v (e.g. VT43N3) - but these only have two legs? will this work in the dimmer?
Check if the pot is wired as a variable resistor, as in the posted circuit diagrams (two pins connected, or one unused).
so if i understand correctly - i would need to work out how fast/slow to flash the LED and that will change the dimmer output in the range i want?
Yes, in principle. The range depends on the sensitivity of the LDR, and on the brightness of the LED. You also have to box the LDR and LED, to keep off other light sources, of course.
But beware, the brightness should be constant, using PWM (pulses!) to change the brightness of the LED may confuse the circuit. I'd first power the LED using a pot, to find out about the achievable range. If that works for you, a RC filter and a transistor may be needed to make the LED light look continuous, not only to the eye, but also to the LDR. In my last experiments I used filament lamps, which react much slower to voltage changes than a LED.
After all it might be easier to attach a servo to the pot. Even then the pot may have to be exchanged, when the servo can only turn 180°, while a pot typically has a 270° full stroke. Finally a true digital pot may be a simpler solution.
DrDiettrich:
Right. But see below for using PWM.Check if the pot is wired as a variable resistor, as in the posted circuit diagrams (two pins connected, or one unused).
it is 2-pin? from the PCB:
so that means the LDR solution could work?
DrDiettrich:
Finally a true digital pot may be a simpler solution.
OK, now that sounds much more simple! are you saying that a digital pot could be used to replicate the mechanical pot on the existing regulator? doesn't that mean it needs to be attached to the 220v circuit side?
OK, i'm not giving up on trying to have no moving parts, but I am struggling to find any examples (e.g. pictures) about "controlling potentiometer with a servo"
I keep getting results showing controlling a "servo with a potentiometer"
do you basically directly connect the shafts? or is it a gear based arrangement?
Servos have a gear box included, that amplifies the weak torque of the DC motor. And yes, you connect the pot shaft to whatever turning part looks out of the servo (shaft or gear wheel).
When you look at the bottom side of your device, you'll see two pot pins connected together. You can solder your LDR in parallel to the pot, for some range detection experiments.
Thanks Doctor, i'm just wondering whether the digital pot is better than the LDR/LED solution?
OK,
alternatively - will this suit my purpose (purpose = control speed of 250VAC 0.5A inline fan)?
http://www.inmojo.com/store/inmojo-market/item/digital-ac-dimmer-module-lite-v.2/
it states:
"Module contains Triac triggering coupled with zero-cross detection mechanism for programming the intensity of incandescent lamps or fan speed controlled through a micro-controller."
The digital dimmer requires exact timing for proper operation. The sample code tends to block the Arduino, not very useful when the processor has to do other things as well.
Wareemba:
Thanks Doctor, i'm just wondering whether the digital pot is better than the LDR/LED solution?
Two considerations:
The LDR/LED combination must be configured for the intended speed range. One problem is, how much the dark resistance will decrease by illumination. As I already suggested: try out yourself, an LDR is not a big waste of money.
For the digital pot, the cheap (integrated) versions are not usable with a dimmer. The pot/motor combinations are perfect but expensive. Here you can try to fit your pot together with a servo.
Wareemba:
speed will be constantly varied - (based on inputs from a pair of DHT22's)(i am actually surprised that an often cited Arduino solution to controlling a variable resistor is a mechanical "put a servo on it" solution?)
so is this the LDR/LED solution in a nutshell?
seems simple enough!
Hey! Can you give me details/source of the circuit diagram?
