I'm currently trying to setup an arduino with a relay to control a mains (110V) switch. In addition, I have a bluetooth serial module that I want to use to interface with the micro controller wirelessly. Unfortunately, both the relay and bluetooth module require a 5v connection. I've tried to power both from the 5v pin, on my Uno, but the neither of the devices work properly. In addition, I tried to power the relay using a digital out pin, but that doesn't provide enough current for the relay. Is there a way I can power both devices using my arduino? The micro controller itself is powered using a 9V battery.
You need to determine the amps required by all boards (arduino, bluetooth, and relay). If you are using a small 9 volt battery, It will not last for more than a few minutes with all these boards at max power, but you may have a monster 9 volt battery. What is the amp hour rating of that battery?
Relays commonly take a lot of drive current. Normally you can't drive a relay from a output pin from the arduino.
Give us more details. How is your power supplied. What boards (url to specs would be good) are you using. Just from initial info, I suspect you need more power, and/or split the power supplies to use two (one for the relay), the other for arduino and bluetooth).
BTW, if you used a SSR (relay) you could probably cut down your 5 volt current requirements, and get by with just one power supply.
could you give the electrical characteristics of the relay and the BT module ?
how much current do they need ?
There are several solutions : use another 5V regulator (or a switching reg.) for the relay and the BT module or just for the relay....
The relay runs on 5V and requires 15-20mA driver current. It is not a solid state relay. The bluetooth module has a working voltage range of 3.5-5.0V. I'm not sure what the power rating of the 9V battery is, just that is one of the standard Duracell 9V batteries.
Thanks for the update. So be aware that the 9 volt battery will not last for to long. You may want to put a volt meter across it when you run the system and see what voltage you have, after 5 minutes, 20 minutes, etc. I suspect, that your 9 volt battery is dropping down to low. But take the readings and let me know what you see.
So you have a relay board!. That makes a difference about the I/O drive, but the amps from the battery are still about the same. Do you have a URL for that relay board?
How long do you want to run this system before the battery dies? Are you able to use a wall wart plug rather than a 9 volt battery?
Or, how does it work if powered through the USB cable?
Satre:
The relay runs on 5V and requires 15-20mA driver current. It is not a solid state relay. The bluetooth module has a working voltage range of 3.5-5.0V. I'm not sure what the power rating of the 9V battery is, just that is one of the standard Duracell 9V batteries.
15-20mA , the Uno should definitely be able to switch the relay . We dion't know anything about the BT module ....
did you try without the BT connected ?
I'd say like Jackwp that the 9V battery is surely too weak (these little 9V batt. are....awful) .
Does it work with arduino powered only via USB ?