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.
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
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.
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?