I just soldered my first project together that has a on off on switch. On one side of the switch is dim leds. On the other side of the switch the same leds are brighter. There is a fan at the end of this circuit. It only runs when the leds are brighter, I'm dropping too much current when the led's are dim.
The fan is a small 5v computer fan. Power source is a 24v wall adapter. Dim side of LEDs is dimmed by 144 ohms, bright side of LEDs is dimmed by 44ohms.
Is there any reason its a bad idea to leave it like this? I should have wired it differently if I didn't want the fan on while switched to the dim setting, but I didn't and now l'm here.
It's my first attempt at my own circuit. I don't mind the fan not turning on while my lights are in the dim setting, I do mind if its gonna catch on fire or something. I’ve learned my lesson on fans and will try not to repeat this offense in the future, but is it okay to keep my display light like this forever?
The circuit will not be stable as the fan is not a constant current device. Use a separate branch to power the fan with its independent resistor. As you progress you will learn how to do it with PWM. I highly recommend you get a copy of the Arduino Cookbook and try any of the projects that interest you. It fives your the circuit, code and explains how it works.
I will take out the fan and diode and replace the 100 ohm resistor with a 340 ohm resistor and replace the 44 ohm resistor with a 60 ohm resistor. I believe this will give me an adequately dim light and a bright light and I will continue to learn circuitry. Thank you for the help!
It would be fine as is? Shouldn’t catch on fire or anything? I do like the idea of the tiny little fan.
The original design was meant for dispersing scent in the room, hence the inclusion of the fan. I’m sure the fan doesn’t actually do much but I just thought it is kinda fun.
That makes sense! Thank you for your time. I will leave it on for longer than the three seconds I’ve been testing it out for and see if anything gets warm.
The three seconds test has passed, I can excitedly report.
With lower voltage the power (related to heat) will be lower. (But the power might be "transferred" to the resistor.)
Some basic electronics math:
Ohm's Law defines the relationship between voltage, resistance, and current as Current = Voltage / Resistance. Resistance is "the resistance to current flow". (This is the 1st thing you learn when you study electronics.)
The basic power formula is Power (Watts) = Voltage x Current.
With Ohm's Law and simultaneous equations you can derive: Power = Voltage Squared / Resistance (often very handy)
and Power = Current Squared x Resistance.
When you add the series resistor you're making a Voltage divider - Wikipedia. As long as you know that resistances in series sum-up, and that the same current flows through series devices, you can apply Ohm's Law to understand how it works.
Ohm's Law (and voltage dividers) are a bit tricky with LEDs and motors because their resistance is not constant. The theory holds but it's not easy making the calculations. LEDs are non-linear and their resistance goes down when voltage goes up. A little too much voltage results in way more current and they are easy to burn-out. That's why you need a series resistor or some other way to control/limit current.
Motors have their maximum current when they are stalled or when they are starting-up. Once the motor is running, current drops. And the load on the motor affects current. With a load (like a fan, or anything) the current is higher than if you are simply spinning the motor shaft.
Dimming & speed control:
With the Arduino, LEDs & motor speed is normally done with PWM and a MOSFET or transistor when you are driving a motor or an LED strip where the Arduino can't supply enough current (and/or enough voltage). PWM switches on & off faster than the eye can see to make an LED appear dim and faster than a motor can respond to control the speed.
If you use linear control instead fo PWM, the MOSFET or transistor will have a voltage drop across it and current through it at the same time. It has to dissipate power and heat (like using a resistor). With PWM its working like a switch and it dissipates much less power. (A regular mechanical switch has virtually no resistance when on. A transistor or MOSFET has a bit more resistance so it still generates some heat.0
