I want my Android phone to control servos connected to an Arduino board, but the power source for everything must be a solar panel connected to a 12V or 6V lead acid battery.
Can this be designed to work?
If will be located permanently outside all year round.
I already have an Android phone powered by a solar panel and 12V battery. That has been running outside now for 3 months. Now I need to add servos controlled from the phone.
I am new to Arduino, so I am still trying to understand how the charging works, power consumption of the board and servos at idle etc, accessory/host mode, what boards and shields will be required etc.
I already have an Android phone powered by a solar panel and 12V battery.
So the tricky part is done :).
The Arduino is much easier to connect than the Android phone but you might get problems with power consumption. If you directly connect the 12V from the battery to a UNO's power connector you'll waste a lot of power because from the 12V input 7V are wasted as heat in the voltage regulator. What you need is a DC/DC converter to get the 12V to stabilized 5V. Probably the easiest way is to choose an Iteaduino (Version > 2.0) which has such a DC/DC converter onboard instead of the linear voltage regulator of a standard Arduino. Depending on the current needs of your servos the power may be enough for them too.
simon99:
I am new to Arduino, so I am still trying to understand how the charging works, power consumption of the board and servos at idle etc, accessory/host mode, what boards and shields will be required etc.
Estimating current draw, and therefore power consumption, can be tricky when you have multiple devices with varying current draws. My suggestion is to do a worst case estimate, e.g. maximum current draw for all perhiperial devices and at least 100 mA for the Arduino board. After you have a prototype design that can handle that, then you can experimentally measure the current draw in the specific situations you are interested in.
Pylon, thank you for the excellent advice. I am a software guy so the straight up fact about regulating vs. converting was really useful. On that subject, for optimal efficiency, am I best to use a 6V lead acid battery? Most of the panels, charge controlling systems and batteries are 12V, so that is the simplest way to go on the supply side, but is the DC/DC converter to take 12V down to 5V as efficient as taking 6V down to 5V? I lack the electrical background.
The specifications say it is a digital servo (I haven't even looked up the implications of that yet...), with an operating voltage of 4.8-6V, 8-9mA idle and 400-500mA no load operating. The specifications are here: http://www.servocity.com/html/hs-5485hb_servo.html. Can this be powered directly from the Iteaduino?
So that means with both servos running concurrently, the power consumption could be 680mA.
But then there is the phone. Back to my original question, can the power come in from an external supply to the board and the servos, but also be charging the phone, which is controlling the board?
If it can, great. Then with the board at 100mA and the phone at up to 500mA, that could be 1280mA total. I wonder if the board can accept that much current?
I have attached a basic drawing of what I am trying to achieve. Can the 12V battery supply power to the Arduino, the Arduino power the phone yet the phone control the Arduino?
For battery operation, a switchmode power supply is recommended. It will efficiently convert 12VDC to 5VDC without wasting much power, no need to use a 6V battery (unless you want to).
Power supply design can be tricky, but if you have $5 to spare there are small integrated supplies like the Murata OKI-78SR-5/1.5-W36-C. It's on a tiny PCB with 3 through-hole pins so it's easy to solder into your project.
Most of the panels, charge controlling systems and batteries are 12V, so that is the simplest way to go on the supply side, but is the DC/DC converter to take 12V down to 5V as efficient as taking 6V down to 5V?
The DC/DC converter should be more efficient in most situations but is a bit more expensive. With 6V at the power connector you won't get 5V after the linear voltage regulator because it has a drop-down of at least 1.5-2V, so you should apply at least 7V to a standard UNO.
Can this be powered directly from the Iteaduino?
Yes, this should be possible. Depends a bit on how much load you will apply.
Back to my original question, can the power come in from an external supply to the board and the servos, but also be charging the phone, which is controlling the board
If you wanna do all at the same time (charging the phone, moving both servos under load and running the Arduino board, it's probably too much for the Iteaduino's built-in converter. Choose an external converter with a higher current capabilitity so you don't have to operate it always at the limit. Example: Mean Well PSD-15C-05 http://uk.mouser.com/ProductDetail/Mean-Well/PSD-15C-05/?qs=sGAEpiMZZMtwaiKVUtQsNf8qVQINUBt5KRemasJUo9Q%3D (I hope the URL is not only visible to me)
If it can, great. Then with the board at 100mA and the phone at up to 500mA, that could be 1280mA total. I wonder if the board can accept that much current?
My Android draws 1A so your 500mA may be a bit low. The Arduino is OK at 100mA but you forget the servos, don't you?
Pylon, thanks for all the feedback. One question and one observation:
I acknowledge your point about possibly needing an external DC/DC converter for excess load. That product you pointed out, Mean Well PSD-15C-05, has an input voltage of 36V. Can you recommend one that accepts a 12V input?
On the Android current, I actually measured the current yesterday drawn from a 12V 5Ah battery to charge a Samsung Galaxy S2 that was dead flat. It drew 277mA for 3.75 hours, after which the current gradually fell off over the next 45 minutes until it because fully charged, at which point it stopped drawing current. Picture attached.
I acknowledge your point about possibly needing an external DC/DC converter for excess load. That product you pointed out, Mean Well PSD-15C-05, has an input voltage of 36V. Can you recommend one that accepts a 12V input?
How about this one? It's made by the same company and has a nominal 12 VDC input, but can accept 9.2 VDC to 18 VDC.
Just to point out something obvious that you may not know, servos usually have a direct connection to some kind of power supply, so the current doing the physical work comes directly to them, not through the microcontroller. Only the low power control signal comes from the microcontroller.
Another servo fact: They create a lot of noise, which is why they should be powered directly, always. They can cause trouble in other parts of your circuit if you power them via the Arduino.
They can cause trouble in other parts of your circuit if you power them via the Arduino.
They can cause trouble in other parts of your circuit even if you power them via another power supply. Careful routing of the power lines AWAY from the Arduino is necessary.
