I have an arduino hooked up to a relay. When it fires it is pulling all the current from the arduino across the relay therefore powering the arduino down. Is the a way of keeping the arduino on for at least a second without using two separate power sources?
What is existing power source? Is your relay driven directly from the uc pin?
My crystal ball sees a rocket scientist, a 5volt power bank, and single relay module powering an igniter.
Leo..
OP has posted the project here.
Not sure if he is asking help with that, or with something else.
Leo..
Yes it's for a launcher. I'm trying to get away from 2 power sources. I have 12v (8x -AA) shorting across relay hooked to an igniter and a 5v power bank for relay and arduino. When I hook the arduino to then same source (with a buck converter) as what is running across the shorted relay everything shuts down with no current running across the arduino. I wanting to try to keep the arduino on for at least a second in this situation. Is there a way to do this?
Sounds like the main battery is not able to keep up (sags below 6volt) with the igniter current.
No idea what an igniter looks like, or what current it draws.
Can you post a link.
A diagram and/or a picture of the setup might help.
Why a relay, and not a logic level mosfet?
Leo..
Hi,
PLEASE!!!
Can you please post a copy of your circuit, in CAD or a picture of a hand drawn circuit in jpg, png?
Then we can advise you.
You should be using the relay as a change over so you charge that cap then switch it off the battery and into the igniter.
Or use a current limit resistor so you do not short the power supply out.
Please a circuit diagram..
Tom.. 
Did we remember a diode across the relay coil?
Here is the schematic.
HFMSchem, on Flickr
jdbwizzard:
Here is the schematic.
Sorry that is a picture, a circuit has all pins and component names and is logically layed out.
Where are the capacitors that are supposed to be on the in and out pins of the vreg?
Check the data sheet of the regulator and see the manufacturers suggested configuration.
The inclusion of a large storage capacitor may help your problem.
Tom...
Is this a 3.3volt Arduino?
If this is a 5volt Arduino, then the output of the external (5volt?) regulator has to connect to VCC, not to V-in(raw). And the BT module needs a voltage divider on the RX pin.
Supply for the igniter needs to connect to the battery directly.
The way the ground wire for the igniter is drawn could create problems.
It's not just the parts, it's also the way you build it.
As TomGeorge mentioned, you need caps on the regulator.
Leo..
The way this is sketched no wonder it doesn't work. You're shorting the batteries through that LED (won't last long of course), at the same time you effectively power down the Arduino (no voltage left, it's shorted) and you will also lose power over the relay, which will then close almost instantly.
As extra bonus, the relay losing power may cause a serious reverse voltage spike over your Arduino, potentially frying it. This, unless there's some fly back diode hidden in your drawing.
You should have caps on the regulator (it will probably work without but is less reliable); unless those caps are really really big they won't be able to power your Arduino even for a second. Caps as per data sheet (typically manufacturers suggest 10-100 uF) are meant to smooth out ripples and to handle sudden changes in current draw.
As you talk about an igniter for a rocket, I guess what you're really trying to do is cause a spark to fly. I'd use a different approach for that: use a capacitor, charge it (slowly - a few seconds maybe) to a high voltage (couple hundred volt or even more - make sure you have a cap that can handle this and the appropriate safety measures), then use a relay or so to switch the capacitor on a different circuit and discharge it through your spark generator.
jdbwizzard:
Yes it's for a launcher. I'm trying to get away from 2 power sources. I have 12v (8x -AA) shorting across relay hooked to an igniter and a 5v power bank for relay and arduino. When I hook the arduino to then same source (with a buck converter) as what is running across the shorted relay everything shuts down with no current running across the arduino. I wanting to try to keep the arduino on for at least a second in this situation. Is there a way to do this?
just a thought.... is the regulator shutting off?
The boost/buck regulator I have requires a 3volt overhead supply, it will turn itsself off if this is not maintained, or an excessive current is drawn, either by the limits you set, or its physical limits (mine is 5A)
http://www.ebay.com/itm/262667368119
If this is the case.. try using a more seperate power supply, then share the GND with the arduino
wvmarle:
The way this is sketched no wonder it doesn't work.
Frequent posters have learned to ignore a Fritzing diagram.
It almost never represents the true situation.
Leo..
Wawa:
Frequent posters have learned to ignore a Fritzing diagram.
It almost never represents the true situation.
Like a formal schematic, I'd say it does show the INTENDED situation, and in this case it matches OPs descriptions quite well (both in how he says he wants to build it, and the result of that build). With all the wiring errors that can be made it's always hard to judge what someone has really built - rather than what they intend to build.
Hi,
Can you please consider this circuit.
It uses a capacitor C4 charged up by your 12V battery and then discharged through the launcher.
This causes less stress in the power supply and how the Arduino performs.
Note the caps around the regulator, they should be as close to the regulator pins as possible.
The value of C4 will have to be calculated or tried in the field, I don't know the energy (joules) required to set the igniter off.
You may even add a potential divider to C4 to signal when the cap is fully charged.
Tom...