How to power a DC motor and Arduino off same battery?

[wingnut]

Hi all

I am trying to control a Ryobi cordless, rechargeable screwdriver, using an Arduino to make it reverse and stop, using two relays. The screwdriver has, I think, a Nimh 4.8V battery from which I am also powering the Arduino circuit and two relays.

Trouble is that when the Arduino switches on the screwdriver motor, the voltage dives from 4.9 to 4.3 V, browning out the Arduino and resetting it.

My son suggests using a LM317 voltage regulator and running the Arduino at say 3.5V, which voltage it can operating at, while running at 8MHz. That way, when the voltage droops, the Arduino will not be shocked. Will this work?

And do you have any other suggestions as to how to run micro's and motors off the same battery?
I have tried using a big capacitor across the Arduino's power pins, but this does not help.

Thanks

 

[(*steve*)]

You need to decouple the cordless drill and the Arduino.

A diode (say a 1N4001) from the power supply feeding a large capacitor may be sufficient. Try a 1000uF 10V capacitor. (The voltage rating may be higher, it doesn't matter)

One end of the diode will have a SSD stripe on it. The end without the stripe goes to the +ve side of the battery. The end with the stripe connects to the +ve side of the capacitor. The -ve side of the capacitor goes to the negative supply from the battery. Power to your Arduino is from the +ve and -ve of the capacitor.

If the drill drags the battery voltage too low for too long, the Arduino will still reset.

You might be reading a voltage of 4.3 volts, but in fact the voltage may be varying from (say) 3V to 4.8V in some complex manner which averages out as 4.3V.

 

[wingnut]

You need to decouple the cordless drill and the Arduino.

A diode (say a 1N4001) from the power supply feeding a large capacitor may be sufficient. Try a 1000uF 10V capacitor. (The voltage rating may be higher, it doesn't matter)

One end of the diode will have a SSD stripe on it. The end without the stripe goes to the +ve side of the battery. The end with the stripe connects to the +ve side of the capacitor. The -ve side of the capacitor goes to the negative supply from the battery. Power to your Arduino is from the +ve and -ve of the capacitor.

If the drill drags the battery voltage too low for too long, the Arduino will still reset.

You might be reading a voltage of 4.3 volts, but in fact the voltage may be varying from (say) 3V to 4.8V in some complex manner which averages out as 4.3V.

Thank you very much Steve. I will decouple the power to the drill from the power to the Arduino, and power the Arduino from the capacitor protected from discharging by the diode. I will try it later today.

 

[wingnut]

Thanks a million Steve, it works!