Hi, I'm building a robot and i'm using this hardware (only a partial list but that's the part that has problems):
Arduino Mega1280
WiShield from LinkSprite (I've done all the rewiring to make this works on a Mega)
USB Shield
Laser Range Finder (LRF)
Basically the USB Shield and a program on the Arduino collects data from the LRF and then the Arduino will sent this data back to the pc through the WiFi connection to be analized live by a pc.
My problem comes with the power supply, since the LRF drains so much current (around 0.8A) and the other two shields together go close to 0.4A, plus the Arduino. Everithing is connected to a LiPo battery 12.1V.
The electronic circuit that deal with the change in voltage from 12 to 5 becomes incredibly hot and I think having more than 1 Amp running through the circut for the whole time (even long) can become a problem.
So I was thinking to 2 different solution:
1* Bending out the 5V-GND pins from the top shield (to open circuit this in respect to the arduino pins) and plug them to an indiependent 5V power source (probably a small circuit using a 7805 Voltage regulator and some capacitors) and plug the battery to the DC supply power plug, in this way through the Arduino will go less current (around 0.25A less) and I should solve "partially" the problem of overheating, maybe I can even plug an heatsink of the electronic circuit that becomes so hot.
2* Make a bigger 5V power supply circuit and make all the current enter through the Vin-GND pins, in this way the current should not be changed in voltage by the electronic circuit on the Arduino and I should avoid overheating, but still remains the problem of more than 1A running through the Arduino circutry.
A DC-DC converter (basically a switching regulator module) would be the easiest solution... ~12V-in and 5V-out... 4 connections... and you're done! An alternative would be to build your own switching regulator. Switching regulators are a bit more complicated than linear regulators, because they require an inductor.
Switching regulators are more efficient than linear regulators. That means they don't get as hot, and your battery lasts longer. With 12V into a linear regulator, the regulator (with 7V across it) is using (wasting) more power than your circuit (with 5V across it)! With a switching regulator, you actually get more current-out than comes-in from the battery (but less voltage of course).
Something easier that might work would be to use two 7805s (the high-power TO-220 kind). One for the Arduino & Shields, and one for the laser gizmo. You'd still have the same total wasted heat/energy, but there would be less stress on the regulators. Heatsinks on the 7805s wouldn't hurt.
DVDdoug:
A DC-DC converter (basically a switching regulator module) would be the easiest solution... ~12V-in and 5V-out... 4 connections... and you're done! An alternative would be to build your own switching regulator. Switching regulators are a bit more complicated than linear regulators, because they require an inductor.
Switching regulators are more efficient than linear regulators. That means they don't get as hot, and your battery lasts longer. With 12V into a linear regulator, the regulator (with 7V across it) is using (wasting) more power than your circuit (with 5V across it)! With a switching regulator, you actually get more current-out than comes-in from the battery (but less voltage of course).
DVDdoug:
Something easier that might work would be to use two 7805s (the high-power TO-220 kind). One for the Arduino & Shields, and one for the laser gizmo. You'd still have the same total wasted heat/energy, but there would be less stress on the regulators. Heatsinks on the 7805s wouldn't hurt.
This seems similar to my solutions n.1, but using 2 circuits. But You would use two 7805 avoiding completely the DC power plug on Arduino.
I already put an heatsink on a 7805 an one on the electric circuitry on the Arduino Mega. If I'm using two circuits as You proposed I'll add another heatsink on the second 7805.
Is the second one a part of a more complex circuit?
No, that is one of the new modular devices, it will work as is (usually these modules require a couple of caps although that one doesn't seem to even need that). TRACO and other people make similar devices.
Is the second one a part of a more complex circuit?
No, that is one of the new modular devices, it will work as is (usually these modules require a couple of caps although that one doesn't seem to even need that). TRACO and other people make similar devices.
How am I supposed to use the second one?
Just plug it in.
Rob
Great! Ok, so I'd just plug this "between" the battery and the Arduino?
Won't have any problem in dealing with this 1A current entering through Vin-GND?
...a more practical question (since I'm not american but I live in CA), where can I find those?? I mean actual shop not online ones... do you have any ideas?? I tried at RadioShack but seems they don't have.
so I'd just plug this "between" the battery and the Arduino?
If you get one that has a higher voltage output you can do that, the TRACO TSR series can be got in say 9-volt versions (TSR 1-2490), you could use that to pre-regulate for VIN on the Arduino.
That OKI-78S is only available in 3v3 and 5v versions, so cannot be used as a pre-regulator because the Arduino needs at least 7 volts on VIN.
I tried at RadioShack but seems they don't have.
No chance I would think.
I live in CA), where can I find those??
I'll have to let a local answer that, however these sort of components aren't normally available in shops AFAIK.
so I'd just plug this "between" the battery and the Arduino?
If you get one that has a higher voltage output you can do that, the TRACO TSR series can be got in say 9-volt versions (TSR 1-2490), you could use that to pre-regulate for VIN on the Arduino.
That OKI-78S is only available in 3v3 and 5v versions, so cannot be used as a pre-regulator because the Arduino needs at least 7 volts on VIN.
I tried at RadioShack but seems they don't have.
No chance I would think.
I live in CA), where can I find those??
I'll have to let a local answer that, however these sort of components aren't normally available in shops AFAIK.
Rob
Thanks so muck!
yeah actually seems pretty hard to get them... no one seems to have them in stock and shipping time are super long. Maybe I'll use the two 7805 in the menawhile... battery duration won't be too much of an issue for the beginning.
CrossRoads:
Please explain why the Murata part, receiving your external voltage and outputting 5V to the Arduino's 5V pin, is not a solution for you?
Are you asking to me?
I think through Vin it's needed to put a voltage that's more than 5 V (around 6 to 12) right?
But anyway I think I'll use the somethink similar to the murata you proposed and I'll attach the 5V output ot hte dcdc converter directly to the 5V-GND pins bending out the 5V-GND connection from the USB-Wifishield to the Arduino. It'd work as an external power supply that won't run thrugh the arduino at all.
The Arduino in the meanwhile will be powered using the DC power jack attaching it directly to the battery.
So basically 2 different power source: one for the Arduino the other one for the shields/LRF
I'll use this: http://www.pololu.com/catalog/product/2110.
Do you think it will work?
I think you did not understand CrossRoads correctly. There's no need to always supply power to the Vin pin (or the power connector). If you do that the power is put on a linear voltage regulator which outputs the 5V. But if you already have stable 5V you can supply that directly to the 5V pin of the Arduino (you need to connect the GND too, of course), circumventing the onboard voltage regulator.
pylon:
I think you did not understand CrossRoads correctly. There's no need to always supply power to the Vin pin (or the power connector). If you do that the power is put on a linear voltage regulator which outputs the 5V. But if you already have stable 5V you can supply that directly to the 5V pin of the Arduino (you need to connect the GND too, of course), circumventing the onboard voltage regulator.
So 5V-GND can be also to put the power in tha arduino?
Cause last time I connected the battery to the 7805 and the 5V regulated supply from the 7805 to the 5v-GND pins... and the WiShield just fried... so I had to buy a new one. It happend immediately, that's why I'm trying to avoid making this connection again and I'm tryng to split or to find a safer way.
So I can put all the current (more than 1 Amp) through 5V-GND with no problem, but 5V-GND has to be the ONLY source of power. right?
Last time I think it was the only source of power, but maybe for a few seconds USB and 5V were plugged together.
Yes. Put the shield on top of the arduino.
Connect +5/Gnd to the power header on the shield.
The Arduino will get the few tens of milliamps it needs from the pins that extend from the shield.
The shield will use the 85/230mA it needs.
CrossRoads:
Yes. Put the shield on top of the arduino.
Connect +5/Gnd to the power header on the shield.
The Arduino will get the few tens of milliamps it needs from the pins that extend from the shield.
The shield will use the 85/230mA it needs.
I think my problem are the restant 800mA requested by the Laser Range Finder that is powered through the USB shield on the Arduino... the total sum of current that is supposed to enter through the 5v-GND is more than 1Amp!
That's my concern... too much current through the pins...
Can you put the 5V/Gnd in using the Laser Range Finde power header? Then its passing on ~250mA the middle card is transmitting. Should be able to handle that.
USB interface is only good for 500mA.