check to see if capacitor is full

as the title says i wanna know how you can check if a capacitor is fully charged. like programming wise and a basic schematic.

something like this. when you hear the cpacitors charge the meter goes up for what i assume is the voltage.

how can you detect how much the capacitor is charged and such.

Measure the voltage across the capacitor.

If the voltage is below 5v, just connect it to an analog pin and analogRead() it.

If the voltage is above 5v, use a pair of resistors as a voltage divider and then analogRead() that.

sorry im a bit new to this.

voltage divider is resisters after the power source but before any component right?

will this effect the voltage over all? will it drain the capacitors?

i picked up the arduino starter kit so im wanting to do a test.

Voltage divider = two high value resistors, in series, connected between two points. At the point between these resistors, the voltage is equal to the ratio between the value of the two resistors. So if you have a cap you expect to be up to 12v, you might put a 20k on the high end, to a 10k resistor, then to the low end (presumably the shared ground). At the point between those resistors, the voltage will be 1/3rd of the voltage between the two ends. Much more information available online.

Yes, it will drain the capacitor if you have to use the voltage divider. The extent to which this will be a problem depends on what you're doing, how big the capacitor is, etc. If it's max 5v, you can measure it directly with the arduino, and this will not drain the capacitor significantly.

What exactly are you doing?

so im feeling incredibly stupid but i think i need a picture to understand what you mean by a voltage divider. im so sorry for not understanding this.

what im experimenting is a basic rail gun. i want to charge the coils enough to give a piece of metal a good launch. i also want to know when the capacitors are at maximum charge.

rail guns and coil guns ALWAYS fascinated me.

I have the arduino uno starter kit.

thanks for the help.

A capacitor will be fully charged when the voltage across the capacitor = supply voltage and the no-load current drops to 'negligible'.

"A capacitor will be fully charged when the voltage across the capacitor = supply voltage and the no-load current drops to 'negligible'. "

Second half of that is chinese. i feel so useless i cant even properly understand whats a parralell circuit and series circuit.

i did all the labs but it feels like i still dont understand anything at all.

See if this helps.

did i get this right?

crossroads how did you upload the image?i dont see any option that lets me do it.

You need to be in the full reply (ie, "reply" on new post, not "quick reply", and "modify" on existing post, not quick edit). Then it's under attachments and other options just below the text box.

I can't get to imageshack links (a lot of them actually my access is blocked). Reply, and Attach the image, as DrAzzy said.

i tried several times it says document is empty....

There was a problem during the uploading of IMG_20150612_150722.jpg. Your post has been made, however the above attachment was not attached. Please use the Back button to edit your post and submit any required changes. The file appears to be empty. Please contact your forum administrator if this continues to be a problem

This is the error.

ok heres a different way to show it.

this is on the breadboard.

5v - a1 10k - b1 / b4 A0 - a4 10k - b4 / gnd

There was a problem during the uploading of IMG_20150612_150722.jpg.

The "problem" is probably the file size. Left single-Click on file in Windows explorer to highlight it. Right-single click on file and select "Open with" , and click on Paint. In upper left hand corner of paint click on "Resize", type in "30" (without quote marks) and hit Enter. Then click on floppy disk symbol in upper left corner to SAVE it. Then select the resized photo as an attachement.

FYI, Google "Voltage divider"

Is this set up right?


what are the resistor values and where do the wires go ?

5v - a1 10k - b1 / b4 A0 - a4 10k - c4 / gnd