# Lowest denominator components to drive salvaged DC motor with 9v battery and Arduino?

I have the following:

• Arduino Uno and/or Duemilanove;
• DC motor salvaged from pound shop toy; and
• a 9v battery.

What are the missing components to drive the motor, in a single direction, with a ON/OFF only functionality? I should probably account for PWM in the future, but always one direction only.

From my very quick investigation probably just a MOSFET and a Zener Diode will be required, but I'm not sure. Oh, and a capacitor to isolate the circuitry wouldn't harm, right?

• perhaps a regulator... hard to say without knowing what voltage the motor runs off of – NickHalden Jul 23 '11 at 0:28
• @Gustavo - Welcome to Electrical Engineering! With some help, I cleaned up your question a bit. Can you clarify how you planned to use a capacitor to isolate the circuitry, and (if you approve of either answer) mark an answer as accepted? – Kevin Vermeer Jul 25 '11 at 3:45
• @Kevin Vermeer Sorry for not accepting yet. Been too busy boxing stuff for the move and I'm limited INet via paired mobile :( – Gustavo Carreno Jul 27 '11 at 15:07
• @Kevin Vermeer The capacitor would be connected as closely as possible to the motor as possible to isolate from the RF feedback the motor produces. I thought that was way basic for me to even mention, sorry. – Gustavo Carreno Jul 27 '11 at 15:08
• @Gustavo - Sorry, that's what I'd call "decoupling". Capacitive isolation usually refers to putting the cap in series to provide a galvanic barrier, for instance you might put one on a communication line so that the devices don't have to share a ground. – Kevin Vermeer Jul 27 '11 at 19:50

## 2 Answers

Since you're talking about a toy motor and a 9V battery, I presume that we're talking low power. So:

• PMV22EN small N-channel MOSFET
• 1k$\Omega$ gate resistor (optional)
• 1N4148 flyback diode

That's two and a half parts.

(the parts linked to are just examples; there are literally hundreds of suitable components)

• One resistor 10k to keep the base current below Arduino output limit
• One high hfe 1A BJT (edit: oh well or mosfet, saves one resistor and diode)
• Three 1A diodes, one in series to motor load to protect power supply from power reverse, one in parallel to motor for break and one in parallel to transistor CE for protection
• One capacitor 100..1000 uF before any load, before diode or after diode, depending on how soft you want to break (decoupling cap from motor through diode will give harder breaks)
• One capacitor 1-10nF in parallel to lytic cap

Total 7 parts. Any lesser amount of parts will increase cost of project by dozen hours of debugging.

Edit: +2 bonus parts: LED and resistor to monitor CPU output. Saves 1-10 hours of debugging the software.

• How does using a mosfet save using a diode? I thought the diode was to protect other components from back-emf. – Dean Jul 25 '11 at 15:53
• Mosfets always come with parasitic diode between source and drain. Also some of the MOSFETs are additionally protected with zeners at the gate – user924 Jul 25 '11 at 17:04