# Powering a rpi and accessory of a 9v battery [closed]

We are trying to use a raspberry pi to record the current going through a dc circuit. The circuit we are trying to measure the current in is powered by a car battery. We have no idea how to record the current and input it into the pi. Plus the entire circuit has to powered of one 9v battery or similar it has to fit into the greenpower f24 regulations. It has to be a pi an Arduino or similar is not an option plus we need the results in a spreadsheet. Thanks in advance.

• How are you planning on measuring the current? What besides the Raspberry Pi needs 9V? Does the Pi need 9V or is that just what you have to power it with? Your question is far too vague to spend time on atm. – I. Wolfe Feb 4 '15 at 16:31
• "need help designing the circuit". So far we have an empty sheet. Thats a lot of help to ask for to fill that from an unknown specification. – PlasmaHH Feb 4 '15 at 16:35
• This seems like it might be a duplicate of electronics.stackexchange.com/questions/65654/… but it depends on what is meant by "9V battery" – I. Wolfe Feb 4 '15 at 16:40
• A RaspberryPi is NOT a low-power device, and a rectangular 9V battery is NOT a suitable power source for it. – Dave Tweed Feb 4 '15 at 16:46
• You'll need an Analog to Digital converter, which the Pi doesn't have. You'd probably be better off using an Arduino which does have ADCs, and consumes much less power than a Pi. – Peter Bennett Feb 4 '15 at 16:51

the entire circuit has to powered of one 9v battery.

It had better be a big 9V battery, or you should have a bagfull of PP3 9V batteries and be swapping them out every few hours minutes.

not this

more like this?
PP10s are no longer made but some ingenuity, cardboard and a box of D-cells might substitute.

You will need an appropriate voltage regulator that can cope with the currents required and dissipate the power for the voltage drop.

We have no idea how to record the current

You'll need to select an appropriate current sensor

You choose one that handles the range of currents you expect and produces a corresponding range of voltages that are within the range a PI Input pin can cope with.

If you are new to this you might play around with a hobbyist breakout like this random example. They should come with documentation that show how to use them.

• You'd be swapping PP3s every few MINUTES, not hours! – Dave Tweed Feb 4 '15 at 17:04
• @Dave: Updated. – RedGrittyBrick Feb 4 '15 at 17:13
• Where did you find a PP10? I haven't seen one of those in decades! :O – brhans Feb 4 '15 at 18:07

Is there any particular reason that you want to use a Pi instead of something else? That is: are you trying to show how to do a project that HAS to use a Pi or are you just trying to get a job done?

You need to provide a whole bunch more information before we can give you any meaningful help.

1) What magnitude of current?

2) What voltage is that current above ground?

3) How much accuracy and resolution do you require?

4) Are you measuring anything else besides this one current?

5) Do you have the freedom to measure current in the ground leg as opposed to the high-side leg?

6) You mention that the whole circuit has to be powered by a single 9V battery. Why? Does it have to be a 9V battery or could it be 4 or 5 single 1.5V cells in series? Can it be powered from something like a large Gel Cell or car battery?

7) What are you doing with the data that you measure?

8) Repeat of question above: does it HAVE to be a Pi?

• OTH, it asks some good questions, and would not fit in a comment (and would suffer from the formatting limitations imposed on a comment). – Wouter van Ooijen Feb 4 '15 at 18:56