Grain of Wheat

Hi All,

I am using the arduino to dim on loop a 12 volt grain of wheat bulb via a transistor
which works fine.

To simplify the installation I would like to share the power supply for the
bulb and the 12 volts for the arduino rather than have two separate
supplies, as the installation will ideally be run from a pack of 12volt AA batteries.

Is there any reason I should not share the same power supply?
Can iI take a power lead from the bulb to power the arduino from the Vin socket.

many thanks

keef476

keef476:
Is there any reason I should not share the same power supply?

Yes. Inefficiency!

If you are going to power this from batteries, then using the linear regulator in the Arduino (which you can do at 12V if you are powering nothing else from the 5V regulator output) will be wasting 60% of the battery power.

It makes more sense to power the Arduino (and use a Pro Mini instead which has no USB to TTL converter to waste more power) from 4.5V - three AA batteries.

I do have to query why you would be using a “grain of wheat” bulb nowadays when these have been functionally replaced - such as in model railways - by white LEDs in the SMD format which can be powered by the same 4.5V without the switching transistor?

Hi Thanks for reply. I prefer the colour of the light from the GOW bulb. Also I have noticed that LEDs seem to dim in progressive stages rather than smoothly which the 12volt GOW bulb does ( very smooth).

I have tried a 3volt GOW bulb but this did not get bright enough -I guess not enough current through the arduino pins.

Any suggestions welcome.

keef476

keef476: Hi Thanks for reply. I prefer the colour of the light from the GOW bulb. Also I have noticed that LEDs seem to dim in progressive stages rather than smoothly which the 12volt GOW bulb does ( very smooth).

I have tried a 3volt GOW bulb but this did not get bright enough -I guess not enough current through the arduino pins.

Any suggestions welcome.

keef476

You need to search for "warm white" led's....

Not sure what you mean by they dim? They dim if being destroyed (too much current)

Hi ,

I mean that I am using the Arduino to dim or fade on a loop. Leds are Ok -just prefer the Gow bulbs .

I just had a look at the Pro Mini - seems ok but needs adapter boards to program. Size looks good for my embedded project.

keef476

keef476: I mean that I am using the Arduino to dim or fade on a loop. Leds are Ok -just prefer the Gow bulbs .

Warm White LEDs are not a bad emulation of an incandescent bulb. You are of course referring to using "AnalogWrite" and noting that the steps are more obvious on the lower levels with a LED. That is of course, due to two effects, one being the thermal inertia of the incandescent bulb, but the other is the linearity of the LED as a light source. At the lower levels of the PWM, the incandescent bulb will not be glowing at all, so you of course, cannot discern the steps. If you do want to dim LEDs, you need to use software PWM with a higher resolution than 256 steps.

keef476: I just had a look at the Pro Mini - seems ok but needs adapter boards to program. Size looks good for my embedded project.

That is precisely the point. You use the adaptor only for programming, then remove it and you are encumbered with neither its bulk nor its current draw.

Hi ,

To revive this thread:

its a good idea to power the arduino from as low as possible to reduce heat and wasted power. I would still like to arrive at an elegant solution which would enable me to have one power supply for the project as this will allow me to switch on and off with one switch as opposed to having two separate supplies i.e. one for arduino and one for the bulb -12 volts, and I assume needing two switches to operate.

Is there some simple way to provide a minimum 4.5 volts for the arduino by a step down of the 12 volt bulb supply which I will have to provide anyway.

Hope I have made this clear. Any suggestions welcome. keef

Buy a switching regulator a couple of bucks off ebay (I got 5 for less than a buck each!)

Then use a couple of decoupling capacitors on the 3-5v output.. but you should be fine without

Hi again,

i have a switching regulator ordered and an arduino pro mini. I would like to know from an earlier post how to hook this up to run from 4.5 volts.( its a 5volt board)

Is it to VCC and ground or Raw and ground.

Many Thanks

keef

If it is a regulated supply - as a switching regulator would be - and is not more than 5V, then you connect it to Vcc.

Great, Thanks

keef