Sharing Voltage/Current

Hi all.

I have an Arduino Mega and an MG811 sensor (http://sandboxelectronics.com/store/images/SEN-000007/SEN-000007_Datasheet.pdf) that I want to power up both from a 9V supply (like this one: http://www.adafruit.com/products/63).

However, I am not sure if I can power both of them with the same supply (split the cable in two plugs), and I don't know if the Ampere is going to be enough. Also I am using 7 more sensors connected to Mega - receiving power from the pins.

I would like very much some help on this, as I don't have special equipment to properly measure everything.

Thanks!

The "datasheet" of your sensor PCB only cares for the 200 mA of heating current, needed for the sensor. You can't really tell for sure, because there is no data available in that so called datasheet. But it is very likely for the other parts of that sensor PCB to draw much less current. So let's say there will be a current demand of 300 mA. The Arduino can be powered from USB, which implies less than 500 mA. That leaves some 200 mA for other parts of your setup. You will have to consider that you don't want to get too close to the maximum current that power supply can handle, or it will destabilize.

What are the other sensors and possible peripherals you want to connect to this same power supply ?

Firstly can you clear up whether you have just the sensor, or the sensor module with built-in power supply for the heater?

With just the sensor you need a precision 6V regulator for the sensor heater, it requires 6V +/- 0.1V, and an omp circuit to boost the output.

If you have the module this is all provided and the device should take about 150mA from 9V (since it uses a switching regulator).

The 9V supply you refer to is 1A so it won't have any trouble (except for a very small probability that the switch-mode generator on the module cannot auto start with only 1A input, but I think it will be fine).

The bare Arduino takes about 30 to 40mA.

You should be fine with what you plan (providing there's no more heating elements)

Ok, so I found a power supply with 9V and 1A, plugged it in Arduino Mega and also connected the MG811 sensor board from the VIN on Arduino (and the Ground), but the power supply couldn't power up Arduino to start at all.

Should I use a power supply with larger Ampere values (i.e. 1.5A or 2A)? Will this work?

Also, what can I do so that the Arduino doesn't get too much heat going from 9V to 5V?

Thanks!

So, options at the moment:

Which one of these choices makes more sense?

*** sigh ***

It seems impossible to build this project with Arduino Mega. I have less than a dozen of sensors, but the power restrictions make it impossible to make this work. Either I have voltage/current not sufficient enough for powering everything, or I use a good power supply that makes Arduino so hot and ready to explode!!!

So why is it so hard to power up a few things using the Arduino Mega? Does this mean that for a rather simple project I need to use 3 or 4 different power supplies??? Can someone advice me what to do here?

Cheers...

There are sensor shields available, which make it easier to connect a multitude of sensors to your board.
There are quite a lot different shields available, so i’d try to find one that is meant for the Mega, and can also power your Mega from that shield.

Does it have to be a power shield or can I use a motor shield to do that?

You must be doing something else wrong there. I power my Megas with a wallwart similar to that one, and although the voltage regulator on the arduino board is burning up 4 volts of heat as it reduces the voltage from 9V to 5V, it doesn't get hot enough to "explode".

So why is it so hard to power up a few things using the Arduino Mega?

Because they take a lot of current.

Does this mean that for a rather simple project I need to use 3 or 4 different power supplies???

No you only need one power supply but it needs to be capable of supplying the power required at the voltage required and does not rely on the Arduino’s voltage regulator.
With that much power what makes you think it is a simple project?

It is frustrating because I have bought a number of items to configure this properly.

So will a MOSFET board like this one will take care of my issues?
http://proto-pic.co.uk/mosfet-power-control-kit/

Or does it need something more sophisticated like these shields:
http://proto-pic.co.uk/power-driver-shield-kit/
http://www.dfrobot.com/index.php?route=product/product&filter_name=power%20shield&product_id=378

Will an Arduino Motor Shield will do the job?
http://arduino.cc/en/Main/ArduinoMotorShieldR3

You told us you have an (meaning single, right ?) MG811 sensor and 7 more sensors. What sensors are that ? You can't expect us to know the needs of your setup and any help with that by not telling us what sensors you have (or their specs). Also, do those sensors need to be powered all the time ?

In case you are using 8 of the same sensors that have a switching supply (based on MarkT's reply #2) , that could be your problem. A switching supply has a rush-in current, and putting 8 of those in parallel, is likely to trigger some over current protection. If so, you might be able to switch on those supplies in sequence and spread this rush-in current. If you have been trying with only a single sensor yet, this is unlikely to be your problem.

Cheers, for the tips.

The reason I didn't mention my other sensors is because they don't draw any significant current, so it is not that important. So, I have disconnected them, and I use only the MG811 shield and a NeoPixel 40 LED shield. Just with these two components the Arduino is overheated in just a few seconds.

The power supply that I use is 9V 3A. So, my previous question remains, what would be the most suitable solution to power this? Can I use any of these shields: http://proto-pic.co.uk/power-driver-shield-kit/ http://www.dfrobot.com/index.php?route=product/product&filter_name=power%20shield&product_id=378

Or can an Arduino Motor Shield do the job? http://arduino.cc/en/Main/ArduinoMotorShieldR3

I am asking because I want to be sure before I make any purchase that it will still not work in my project. So I need your advice if possible...

The first shield is meant to have your Arduino control loads. It is a set of switches which are controlled by your Arduino. It has an Uno form factor, meaning you cant use it to simply stack other shields on it that were designed for your Mega.

The motor shield is meant to control motors or other (inductive) loads. Also Uno form factor.

Those are not power supplies.

The power shield is a power supply. You cannot control it using your Arduino, you have to set it using a potentiometer. It has a LED bar that will show you you're supplying 3.3, 5, 9 or 12 volts. This means the LEDs cannot tell you are supplying 6 volts or 10 volts (so values in between). It has a connection to A0, meaning you can read out the set voltage if you set the jumper (so leaving it open removes this option and frees up A0). Maximum output current is rated 2 A continuous. And this one too has an Uno form factor.

You can use this as a power supply to your peripherals, i wouldn't use it to power the Arduino itself. Also, i would never use those LEDs as read out, i'd use a multimeter.

By the way, did you check for any wiring mistakes, and also have someone else check that (most people tend to not see their own mistakes).

Thank you MAS3, this was very helpful response.

I am thinking to use this voltage regulator (http://www.adafruit.com/products/1385) to go from 9V to 5V and supply the necessary current for the NeoPixel shield.

Then, I will try a couple of things for powering up properly MG811 as well. One option will be to use the Power Shield I wrote about before, or just use a splitter for the power supply cable (http://d114hh0cykhyb0.cloudfront.net/images/uploads/LED-Power-Supply-Connection-Splitter-qtr-CPS-M2F.jpg).

Will do some tests and see what happens.

It’s a good decision to split the power supply cable before that power enters the Arduino board.
This way you are not overloading your on board power supply of the Arduino.
However, that splitter cable doesn’t directly plug into the UBEC you are considering at the moment.
Consider also ordering a barrel plug that goes into that splitter (or in your Arduino power plug), and solder that instead of the connector at the output of that UBEC.

The cable goes to the MG811 shield. The Ubec is connected from the VIn and GnD of the Arduino, goes down to 5V/3A and then to Neopixel shield.

That cable has 3 ends, and you have only one end connected (to the MG811) in your last description. Where do you plan to put at least 1 other end ? The barrel connector to power the Arduino is an input, it can not be used as an output (just in case you were planning to use that one for this). It is connected to a diode and a regulator that prevent this.