Noise from motor trashing IC

I am experiencing noise and voltage drops when a pager motor is turned on and off via a PWM signal from the IC. After about 2 days of continuous operation it is frying the IC.

I am looking for guidance on how to isolate the IC from the motor so that the voltage fluctuations that occur when the motor starts & stops don’t affect the IC.

I’ve attached 2 images:

  1. breadboard view
  2. schematic

The sketch on the IC is basically an analog version of the Blink example.

The minimum requirements for this project are:

  1. It must run off of a 3V coin cell battery, and no more than two 3V coin cell batteries
  2. It must use an IC, I am using an ATTiny85
  3. The motor must be no bigger than a Pager motor

Ideally, I would like to run with two 3V coin cell batteries; one for the IC to pump the transistor & one to drive the motor via transistor.

If I run this sketch with an LED instead of a motor it will last for a little over one week.

Any suggestions on how to isolate the motor from the IC? Or, “Well, there’s your problem…”

Here is the BOM on the breadboard:

D1 Rectifier Diode (1N4001)
IC1 ATTiny85
M1 DC Motor (Pager Motor)
Q1 NPN-Transistor (PN2222A)
R1 10k Resistor
VCC1 3V Coin Cell




Start here:

The short of it - you need an isolation capacitor across the motor leads, and a capacitor (as close to the microcontroller as possible) across the positive rail to the ground rail. That, or use an optocoupler. Or a relay.

Read parts 2-4 as well on the site. Mike is long known around here as "Grumpy Mike" - you might've run into him before...

You need a minimum of a 100nF ceramic decoupling capacitor and something like 470uF -- 3300uF electrolytic as well to handle motor transients/spikes. All digital electronic circuits need proper decoupling - and if a motor's involved its good policy to use entirely separate supplies if possible because of the inductive spikes and crow-barring of the motor supply.

Thanks cr0sh & MarkT.

I'll take all of this in and give it another shot.

Thanks, -Mike