i would like some help with a project.
I need to control a small 3volt filament bulb to make it fade on a loop.
I have already made a version which operates on 3 AA batteries using
pro mini and a Mofset IRF 540 which works fine.
I now need to make the same but powered from a mains adapter - say 4.5volts.
I have a 3.3 volt Pro mini.
I would like to know if this is the best option to power the unit and which mofset
would be best to use.
(I would prefer to power from 12volts as I have lots of other objects which all use 12volts But I don't know if this is practical.)
Do you know what the amperage requirement of the bulb is? Maybe it's small enough to power from the 3.3v pin on the board? Usually a bad idea to use the board as a power supply but might be okay for a single bulb.
You can use a buck converter to lower the 12VDC to whatever you want within reason. Look at the specs before purchasing, it will give you an input range which must include 12V for your application and 4.5V in the output. They will have a range that they will provide and the output is generally adjustable with a pot. These can be gotten in the dollar range.
Yes I have tried this in the past but I think it takes a bit too much current. About 0.16 amp.
I don't know if any of the other boards can supply a bit more current. This would make my life easier if so.
It is basically a 3volt Grain of wheat bulb. Not sure if it has a part number.
Here is the spec:
Sub Miniature Bulbs
65ma
3.0mmx10mm on 120mm insulated wire leads.
For 3v or 6v V AC or DC Operation.
3mm dia diameter. Insulated wire leads
Resistor required for 12V operation
Since you have 12 volts I would just use a common off the shelf buck converter. [These are very common.](https://I would like to know if this is the best option to power the unit and which mofset would be best to use.) Max current is 3.0 amps and your lamp at 65 mA is not a problem. I would just drive the bulb with a 2N2222 transistor rather than use a MOSFET. My reasoning for a 2N2222 over a MOSFET, even a logic level MOSFET is the MOSFET gate voltage required and your lamp load is only 65 mA.
Hi,
So I have the transistors. I have tried wiring them into the circuit but no luck so far.
Either the bulb is lit continually or will not light at ll.
The circuit is:
Emitter pin connected to ground.
Base pin is connected to pin 9 on pro mini via a resistor.
Collector pin is connected to the bulb which then goes to vcc.
With a high applied to transistor base the lamp should light and with a low applied to transistor base lamp should be off. This assumes a Vcc of 3.0 or 3.3 volts. Make sure the pinout for the transistor is correct. There are a few variations of the 2N2222 transistor.
You can test the circuit using the blink (with delay!) sketch so it goes on and off slow enough to see, the output pin would directly power an LED with a 1K series current limiting resistor wired to ground.
The driven lamp would go,on and off in sync.
Works, then try the PWM. Which should also, but you might see that while both get brighter and dimmer in synchrony, the visual effect will be different due to LEDs are not incandescent grains o' wheat.
I should have asked about the base resistor. With about 70 mA collector current you want about 7 mA base current so lets say 3.3 V - 0.7 volts (base emitter drop) = 2.6 volts 2.6 volts / 7 mA = 371 Ohms so lets just use a standard 330 Ohm resistor on the base. This is the simple approach.
Ron
