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Electronics => Electronics => Topic started by: extreme.aly on March 10, 2015, 07:19:28 AM

Title: Pololu Motor Encoder 5V to 3.3V
Post by: extreme.aly on March 10, 2015, 07:19:28 AM
Hello people,

I tried googling this but I cannot find the datasheet for the encoder that comes with Pololu's 37dx52l Motor.

I'm trying to use that encoder to get motor speed on a Beaglebone Black which is 3.3V tolerant. So I made a voltage divider circuit with 1K and 2K ohm resistors. But for some reason, it is giving me way less than 3.3V.. Like 1.3V on the output of the voltage divider.
I noticed that the original signal, 5V expected, also changed to 2V. (2V*2/3 = 1.3V)...

Can anyone suggest a solution for properly dropping down the voltage to 3.3V for this Motor Encoder's output?
Title: Re: Pololu Motor Encoder 5V to 3.3V
Post by: bdeuell on March 10, 2015, 11:22:00 AM
Are you powering the encoder with 3.3v (encoder Vcc, blue wire)?

how are you measuring the voltage of the encoder signal?

Title: Re: Pololu Motor Encoder 5V to 3.3V
Post by: extreme.aly on March 11, 2015, 05:56:41 AM
I'm powering the encoder using 5V.

I was measuring the voltage between GND and the encoder out pin.

I found a way to fix it. I used 10k and 20k ohm resistors instead of 1k and 2k.

My theory says that the encoder was not able to supply enough current, so the voltage was dropping. I used resistors of higher value so that less current is drawn. Lesser voltage is dropped.
Title: Re: Pololu Motor Encoder 5V to 3.3V
Post by: mklrobo on March 11, 2015, 06:31:52 AM
 :) Hello!
Check out this site;
https://www.pololu.com/product/1102 (https://www.pololu.com/product/1102)
Site with integrated encoder;
https://www.pololu.com/product/1442 (https://www.pololu.com/product/1442)
The specs are;
Dimensions
Size:  37D x 64L mm 
Weight:  7.5 oz 
Shaft diameter:  6 mm 

General specifications
Gear ratio:  19:1 
Free-run speed @ 6V:  256 rpm1 
Free-run current @ 6V:  250 mA1 
Stall current @ 6V:  2500 mA1 
Stall torque @ 6V:  42 oz·in1 
Free-run speed @ 12V:  500 rpm 
Free-run current @ 12V:  300 mA 
Stall current @ 12V:  5000 mA 
Stall torque @ 12V:  84 oz·in 
Lead length:  11 in 
 ;D ;D ;D Hope this helps on the parameters of the
motor. ;D ;D ;D
Title: Re: Pololu Motor Encoder 5V to 3.3V
Post by: extreme.aly on March 11, 2015, 07:19:51 AM
:) Hello!
Check out this site;
https://www.pololu.com/product/1102 (https://www.pololu.com/product/1102)
Site with integrated encoder;
https://www.pololu.com/product/1442 (https://www.pololu.com/product/1442)
The specs are;
Dimensions
Size:  37D x 64L mm 
Weight:  7.5 oz 
Shaft diameter:  6 mm 

General specifications
Gear ratio:  19:1 
Free-run speed @ 6V:  256 rpm1 
Free-run current @ 6V:  250 mA1 
Stall current @ 6V:  2500 mA1 
Stall torque @ 6V:  42 oz·in1 
Free-run speed @ 12V:  500 rpm 
Free-run current @ 12V:  300 mA 
Stall current @ 12V:  5000 mA 
Stall torque @ 12V:  84 oz·in 
Lead length:  11 in 
 ;D ;D ;D Hope this helps on the parameters of the
motor. ;D ;D ;D

Obviously I have seen this page. I'm talking about the datasheet of it's encoder. This page doesn't mention the part # of the hall sensor encoder it is using.
Title: Re: Pololu Motor Encoder 5V to 3.3V
Post by: bdeuell on March 11, 2015, 10:11:08 AM
I found a way to fix it. I used 10k and 20k ohm resistors instead of 1k and 2k.

My theory says that the encoder was not able to supply enough current, so the voltage was dropping. I used resistors of higher value so that less current is drawn. Lesser voltage is dropped.
sounds like a reasonable explanation to me, glad you figured it out.

I would not be surprised if the encoder is a custom board (as it is soldered directly to the motor). If you still need additional information regarding the encoder i would try contacting Pololu, if this is a custom encoder board they might be able to supply part numbers for the components they used.
Title: Re: Pololu Motor Encoder 5V to 3.3V
Post by: SirDan on March 11, 2015, 04:52:59 PM
Hello.

Just curious. Were you able to try any higher resistor values, like 50K and 100K?

My favorite resistor divider calculator.
http://www.voltagedivider.ca (http://www.voltagedivider.ca)

Thanks,
Dan