# Input current.

I have seen several references to this, but was wondering. I want to use a 32 V DC power supply for my project. I know the max input voltage for the Arduino is 20V. If I remember my college EE I should be able to put a resistor in series with the power to drop the voltage to something less than 20V, but I need the current draw to apply Ohm's law V=IR.

I haven't played with electronics for about 50 years so my theory may be wrong. Any suggestions other than using a separate power supply for the Arduino?

Thanks.

Use a DC-DC switch-mode regulator to do the step down from 32 to 5V. Don't use a resistor, don't use a linear regulator.

If I remember my college EE I should be able to put a resistor in series with the power to drop the voltage to something less than 20V,

Problem is that you don't remember your college EE well enough. That will only "work" if the current taken by the load is constant which it is very much not.

In fact I don’t remember any of my College EE except V-IR. It confounded me then and it continues to today and, it was over 50 years ago. You would think someone with an MS in Aeronautical Engineering would be able to get this, but it alludes me.

Thanks for your patience and information. I am still trying to track down a DC-DC regulator. Finding lots of different types, from simple chips, to complete boards with pots to adjust output voltages. Just don’t know which one to go with so any recommendations would be appreciated.

Have a look at Pololu to get an idea of what's available in switching regulators. These will give you a steady output voltage for a range of input voltages. With a 5V one of these you can bypass the Arduino regulator.

You can also get cheaper buck regulators where you can adjust the output voltage with a trim pot, but the output voltage will change if the input voltage changes, so you may still need the Arduino regulator if your power supply is not constant (like a battery).

ov10fac: In fact I don't remember any of my College EE except V-IR. It confounded me then and it continues to today and, it was over 50 years ago. You would think someone with an MS in Aeronautical Engineering would be able to get this, but it alludes me.

Thanks for your patience and information. I am still trying to track down a DC-DC regulator. Finding lots of different types, from simple chips, to complete boards with pots to adjust output voltages. Just don't know which one to go with so any recommendations would be appreciated.

How long can you wait for shipping? If 3-4 weeks is okay then alibaba, dealextreme and ebay will sell you a buck converter with 3A max output for about \$3, less if you buy 3 or more.

V-IR... you mean Ohm's Law?

How many milliAmperes do you need?

If it is not more than 50 thru 1000 milliAmperes at 5 Volts you might use the power supplies of rotten devices. People throw them away every day.

In Germany we have a very good recyling system. There are recycling yards where you can get rid of waste and broken things. You are not allowed to take things, but nobody cares. So I have a box foll of different power supplies. Cost is ZERO. And I feel good reusing things that have been thrown out. The power supplies are usually good, just the devices were either too old or not working anymore.

Do you want to connect high power devices to your Arduino? If not - forget about 32 Volts.

If you do not need more than 100 milliAmperes you might use a linear voltage regulator, but it will waste up to 2 Watts when you go down from 32V to 10V. Not good, but acceptable if you live in a country where power is cheaper than in Germany (almost any country).

I recommend to power the Arduino not directly using the 5V pin if you cannot guarantee voltage stability. An input voltage of 9V seems to be perfect. For higher currents please go down to an input voltage of 7,5 Volts.

arduinoaleman: How many milliAmperes do you need?

If it is not more than 50 thru 1000 milliAmperes at 5 Volts you might use the power supplies of rotten devices. People throw them away every day.

In Germany we have a very good recyling system. There are recycling yards where you can get rid of waste and broken things. You are not allowed to take things, but nobody cares. So I have a box foll of different power supplies. Cost is ZERO. And I feel good reusing things that have been thrown out. The power supplies are usually good, just the devices were either too old or not working anymore.

Here we have yard sales and GoodWill Industries.

How many of those free power supplies are old design low efficiency linear supplies that waste power even when not use but still plugged in? They are easy to tell by the weight, high efficiency supplies are light due to lack of transformer. They are easy to tell by how they stay warm (big clue) while plugged in even when not being used to power anything.

Don't just throw out the old though, they have a transformer and parts than can take a good amount of current. Big ones can be used for door stops and boat anchors!

For a couple EU you should be able to get 5V 1A. Arduino boards like Uno are rated at using 200mA max. Extra supply capacity means the PS does not work itself to death so soon, a 1A supply delivering 100mA should last a long time.

A good switching PS or (also switching) buck converter is over 90% efficient where a good linear PS might be 70%.

But in Germany where so much power is green and price is low(?) perhaps a little waste is not such a sin?

davidrh: Have a look at Pololu to get an idea of what's available in switching regulators. These will give you a steady output voltage for a range of input voltages. With a 5V one of these you can bypass the Arduino regulator.

You can also get cheaper buck regulators where you can adjust the output voltage with a trim pot, but the output voltage will change if the input voltage changes, so you may still need the Arduino regulator if your power supply is not constant (like a battery).

Thank you. I will check them out.

GoForSmoke: How long can you wait for shipping? If 3-4 weeks is okay then alibaba, dealextreme and ebay will sell you a buck converter with 3A max output for about \$3, less if you buy 3 or more.

V-IR... you mean Ohm's Law?

Appreciate that information. I can wait. Yes, Ohm's Law. That was a fat finger error. Should have been V=IR which of course is the correct equation.

arduinoaleman: How many milliAmperes do you need?

If it is not more than 50 thru 1000 milliAmperes at 5 Volts you might use the power supplies of rotten devices. People throw them away every day.

In Germany we have a very good recyling system. There are recycling yards where you can get rid of waste and broken things. You are not allowed to take things, but nobody cares. So I have a box foll of different power supplies. Cost is ZERO. And I feel good reusing things that have been thrown out. The power supplies are usually good, just the devices were either too old or not working anymore.

Do you want to connect high power devices to your Arduino? If not - forget about 32 Volts.

If you do not need more than 100 milliAmperes you might use a linear voltage regulator, but it will waste up to 2 Watts when you go down from 32V to 10V. Not good, but acceptable if you live in a country where power is cheaper than in Germany (almost any country).

I recommend to power the Arduino not directly using the 5V pin if you cannot guarantee voltage stability. An input voltage of 9V seems to be perfect. For higher currents please go down to an input voltage of 7,5 Volts.

As a mater of fact I do the same thing here. I have a friend who is in the recycling business. I get 12 and 24 Volt DC power supplies from him very inexpensively. Glad to see good ideas are the same the world over.

GoForSmoke: Here we have yard sales and GoodWill Industries.

How many of those free power supplies are old design low efficiency linear supplies that waste power even when not use but still plugged in? They are easy to tell by the weight, high efficiency supplies are light due to lack of transformer. They are easy to tell by how they stay warm (big clue) while plugged in even when not being used to power anything.

Don't just throw out the old though, they have a transformer and parts than can take a good amount of current. Big ones can be used for door stops and boat anchors!

For a couple EU you should be able to get 5V 1A. Arduino boards like Uno are rated at using 200mA max. Extra supply capacity means the PS does not work itself to death so soon, a 1A supply delivering 100mA should last a long time.

A good switching PS or (also switching) buck converter is over 90% efficient where a good linear PS might be 70%.

But in Germany where so much power is green and price is low(?) perhaps a little waste is not such a sin?

Thank you for the information and advice.

ov10fac: Thank you for the information and advice.

If you want some good reading to get you back up to speed, look into the hyperphysics site.

The kind of electric we mostly get into here is DC. You want to get Ohm's Law and Kirchoff's Laws down to be able to design simple circuits.

Look at it this way, there's a lot of new and easier to use toys than you had before, and they're wayyy cheaper! Well, not as much if you want to run power, part of it is that now the toys use less V and I than they used to.

You have a good 10-15 years on me and I need magnification to get jumper pins in the right holes. Following help here (IIRC from AWOL or Grumpy_Mike) I went out (to Harbor Freight) and got the best magnifier visor they had with the interchangeable lenses. I might still go for extra strong reading glasses or clip-ons. Harbor Freight is also where I got my compartment cases with compartments big enough (about 2.5" square) to put resistors without having to bend them first, big enough for labels in the bottoms. They're \$4 each with latched see-through lids. Before those I had everything in the bags they came in from allelectronics, a salvage house I bought from... they got some neat parts but not quite Hong Kong low prices.

Also for jumpers, look for DuPont Cables. That's multicolor 40-wire ribbon cable with each wire ending in a pin or hole. The female ends are perfect for header pins on boards and adapters. You peel off as many strands as you need and.. instant cable. For breadboarding there's also a different kind of jumper made from wire-wrap wire. A set can run about \$6 for 150 pieces of varying length and colors. It's straight insulated wire with stripped ends bent at 90 deg... they can be a pain inserting and removing from breadboards (I need needle nose pliers) but they lay flat on the board (you'll have to bow them to one side a bit) and stay in place really well, next to permanent well.

Hey once you get past the many things at once lesson, maybe you could make some cool fixed-wing fliers?

@GoForSmoke

Energy prices in Germany are almost the highest on this planet.

People throw away their iPhones every 3 years, the TV sets every 4 years. Most mobile phone power supplies will give you 500mA at 5 Volts. Perfect for electronics.

I am definitely not using power supplies older than a couple of years.

And reusing working devices like power supplies is environmentally very positive. They consist of so many different materials that they are hard to recycle.

arduinoaleman: Most mobile phone power supplies will give you 500mA at 5 Volts. Perfect for electronics.

GoForSmoke:
If you want some good reading to get you back up to speed, look into the hyperphysics site.

Wow, like an unmoderated on-line class room. Easy to follow and it actually makes sense. Read a few things about Ohm’s law, voltage and current law and lessons from long ago came back to me. Maybe after all these years I might finelly understand how electronics actually work (at least at a basic level).

GoForSmoke:
The kind of electric we mostly get into here is DC. You want to get Ohm’s Law and Kirchoff’s Laws down to be able to design simple circuits.

Look at it this way, there’s a lot of new and easier to use toys than you had before, and they’re wayyy cheaper!
Well, not as much if you want to run power, part of it is that now the toys use less V and I than they used to.

You have a good 10-15 years on me and I need magnification to get jumper pins in the right holes. Following help here (IIRC from AWOL or Grumpy_Mike) I went out (to Harbor Freight) and got the best magnifier visor they had with the interchangeable lenses. I might still go for extra strong reading glasses or clip-ons. Harbor Freight is also where I got my compartment cases with compartments big enough (about 2.5" square) to put resistors without having to bend them first, big enough for labels in the bottoms. They’re \$4 each with latched see-through lids. Before those I had everything in the bags they came in from allelectronics, a salvage house I bought from… they got some neat parts but not quite Hong Kong low prices.

Yep HF is my friend. I have the same visor I use for fly tying and fly rod building. I too use magnifiers, usually 3X. I Also use those very same boxes, I also use cabinets that hang on the wall. They have 15 or 20 drawers and are very good for this kind of thing. I think I only pay \$15 at Menards.

GoForSmoke:
Also for jumpers, look for DuPont Cables. That’s multicolor 40-wire ribbon cable with each wire ending in a pin or hole. The female ends are perfect for header pins on boards and adapters. You peel off as many strands as you need and… instant cable.
For breadboarding there’s also a different kind of jumper made from wire-wrap wire. A set can run about \$6 for 150 pieces of varying length and colors. It’s straight insulated wire with stripped ends bent at 90 deg… they can be a pain inserting and removing from breadboards (I need needle nose pliers) but they lay flat on the board (you’ll have to bow them to one side a bit) and stay in place really well, next to permanent well.

Do you know the AWG for the wire wrap and where did you purchase your jumpers?

GoForSmoke:
Hey once you get past the many things at once lesson, maybe you could make some cool fixed-wing fliers?

Thanks for the information.

I use mobile phone power supplies for my Raspberry Pi power source. I agree, they work really well for that purpose. I didn't know you could use it on the Arduino too. So the Arduino can be powered from the USB port? Guess I need to re-read the manual.

So the Arduino can be powered from the USB port?

Yes.

ov10fac: Wow, like an unmoderated on-line class room. Easy to follow and it actually makes sense. Read a few things about Ohm's law, voltage and current law and lessons from long ago came back to me. Maybe after all these years I might finelly understand how electronics actually work (at least at a basic level).

You've got resources you don't even know about. I keep a browser open when I code, tabs open to the Arduino on web pages I need and all zoomed in to easy-read size. It's way easier to use than my old reference manuals.

Yep HF is my friend. I have the same visor I use for fly tying and fly rod building. I too use magnifiers, usually 3X. I Also use those very same boxes, I also use cabinets that hang on the wall. They have 15 or 20 drawers and are very good for this kind of thing. I think I only pay \$15 at Menards.

I haven't gone dry fly fishing since 1972. What an experience every time! Come alive when the trout hits!

Do you know the AWG for the wire wrap and where did you purchase your jumpers?

Thanks for the information.

It says 22 ga where I got the set. The fit in breadboard holes is snug, they stay in place but are a pain for trying quick check work. http://www.allelectronics.com/item/jw-140/140-piece-jumper-wire-assortment/1.html

Neat junk and not so neat junk. Prices neither best nor worst. They don't have DuPont Cables.

I pay less than \$3 for 1A 5V regulated switching PS wall warts from China. That's all I need for most things 5V. But these 5A boxes for \$7, I might jump though it'd be easier if I lived in Van Nuys! http://www.allelectronics.com/item/ps-255/5vdc-5-amp-25w-power-supply/1.html

If you spend idle time shopping around before buying, ahhhhh you know!

So the Arduino can be powered from the USB port?

And communicate if the port's not just a charger but a PC USB. That's how you get the IDE program into the chip (the easy way at least) and IO with Serial Monitor or your own program or terminal emulator. Since IDE 1.6 the max USB serial rate is 250000 baud, into SPI bus speed. You don't have to wait long for the serial output buffer to empty at that rate, it's 40 microseconds per char and yes, Arduino can do useful things in between -- that's 640 cycles on an 8 bit RISC.

arduinoaleman: @GoForSmoke

Energy prices in Germany are almost the highest on this planet.

People throw away their iPhones every 3 years, the TV sets every 4 years. Most mobile phone power supplies will give you 500mA at 5 Volts. Perfect for electronics.

I am definitely not using power supplies older than a couple of years.

And reusing working devices like power supplies is environmentally very positive. They consist of so many different materials that they are hard to recycle.

Not to mention the cost of making those PSU's.

The electric is so high because of taxes or other manipulation? Lot of people making wind and solar on their own?