DRV8871 incorrect function

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93rsimpson
 
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DRV8871 incorrect function

Post by 93rsimpson »

Hi,

I have a DRV8871 breakout board that i was going to use to power a solenoid, but i can only get it to provide an output when IN2 is high.
To demonstrate/test I have a raspberry pi providing 5v to let me pull IN1 or IN2 high, and a 9v battery on the VM to provide power. Firstly I applied 5v t IN2 and IN1 to GND, which resulted in reading of 9.5v from the output. Then I applied 5v to IN1 and IN2 to GND, which resulted in 0v from the output.

The images below are the test circuit. left side of board is connected to 5V and GND on raspberry pi. Right side to 9v battery.
Image
IN1 high

I think the linked topic is similar/identical to my issue.
viewtopic.php?f=19&p=788854

I am hoping support can help me fix this.

Thanks
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dastels
 
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Re: DRV8871 incorrect function

Post by dastels »

How are you measuring the output voltage? Between what points?

Dave

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adafruit_support_bill
 
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Re: DRV8871 incorrect function

Post by adafruit_support_bill »

What solenoid are you using? Do you have a datasheet? A plain solenoid coil does not care about polarity. But some solenoids have a built-in snubber diode for the kickback, so they will only work when powered in one direction.

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93rsimpson
 
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Re: DRV8871 incorrect function

Post by 93rsimpson »

I’m using a fairly basic multi meter to take the voltage reading. A laser 3533.

The solenoid is part of a bell, I’m using a motor driver to alternate direction to make it ring. I don’t have a data sheet for it but I have been able to actuate it one way with the driver. It needs 12v, I’ve just used 9v here to demonstrate the problem.

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sj_remington
 
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Re: DRV8871 incorrect function

Post by sj_remington »

If you are measuring the motor output voltage with respect to "9V" battery negative, you got the expected result.

A more instructive test is to measure the voltage across the motor output terminals.

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93rsimpson
 
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Re: DRV8871 incorrect function

Post by 93rsimpson »

Sorry, I am measuring across the motor output pins.

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dastels
 
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Re: DRV8871 incorrect function

Post by dastels »

OK, then it should which between +9 and -9 since it's an H-Bridge.

If you are just using a solenoid, https://www.adafruit.com/product/5648 might be a better (and certainly simpler) choice.

Dave

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93rsimpson
 
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Re: DRV8871 incorrect function

Post by 93rsimpson »

I have just got the 5v mini push-pull solenoid to see if i can get it to work with the bell, so i might try that driver, thanks.

The armature in the solenoid I already have is unsprung, so i needed a H-bridge so i can alternate the direction and create the ringing action. The armature is retained by the bell housing, so it rings it from inside the bell. I don't have an image at the minute to upload.

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dastels
 
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Re: DRV8871 incorrect function

Post by dastels »

OK, if you need push-pull operation, then the H-Bridge driver is right.

have you read the tutorial? https://learn.adafruit.com/adafruit-drv ... r-breakout

Dave

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93rsimpson
 
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Re: DRV8871 incorrect function

Post by 93rsimpson »

Yeh, followed everything I need to to try get it working. But not having any luck.

I had another H-bridge driver that works as expected, but I can’t use it for this project as I can’t go past 10v ish.

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dastels
 
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Re: DRV8871 incorrect function

Post by dastels »

Can you try this board with a motor?

Dave

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93rsimpson
 
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Re: DRV8871 incorrect function

Post by 93rsimpson »

I don’t have a motor to try it with. I tried a python script that alternated the direction the. Used LEDs to see if it was working before I tried it on the solenoid. Script worked fine, it worked on the othe H bridge I have, but I only get one LED working on the DRV8871

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dastels
 
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Re: DRV8871 incorrect function

Post by dastels »

It sounds like the driver may be bad. Please email [email protected] with a link to this thread, your order number, and request the replacement of one DRV8871 DC Motor Driver Breakout.

Dave

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