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Author Topic: Noise from motor trashing IC  (Read 568 times)
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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

Thanks,
-Mike


* breadBoard.png (33.69 KB, 363x579 - viewed 13 times.)

* schematic.png (30.25 KB, 915x619 - viewed 16 times.)
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Start here: http://www.thebox.myzen.co.uk/Workshop/Motors_1.html

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...
« Last Edit: March 21, 2011, 11:05:49 pm by cr0sh » Logged

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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.
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Thanks cr0sh & MarkT.

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

Thanks,
-Mike
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