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Author Topic: 8825 FAULT pin  (Read 3666 times)

GigiG

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8825 FAULT pin
« on: January 11, 2015, 18:28:44 »
I tested one stepper with an DRV8825 (attached figure) and it works fine! I have only a doubt about the 8825's FAULT pin. In your schematics the pin 10 of the Motor Driver (labeled as VDD) is connected to +5V togheter with a ceramic 100nF capacitor. It seems that this schematics refer to an A4988 Pololu driver. What do I have to do with the corresponding 8825's FAULT pin? In the setup shown in the figure I left this pin unconnected. Did I do the right thing?

I've also a concern about EQASCOM usage, sorry because it's out of topic and I'm new to EQASCOM settings. I tried a Slew command in CdC (goto a selected star), the stepper accelerate but it runs at a slow speed to reach the target and is vibrating a lot. Manually (using the Slew Controls of the EQASCOM interface) the stepper perform very well at speeds like 500-600x without stalling. I expected to see the goto movement in CdC performing at the selected slew speed but it seems that it is much slower.
Gigi
 
« Last Edit: January 11, 2015, 20:21:45 by GigiG »
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TCWORLD

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Re: 8825 FAULT pin
« Reply #1 on: January 11, 2015, 21:42:01 »
Hi,

The Goto speed is set in the configuration utility. There are two boxes (one for RA and one for DEC) which are labelled something like 'Goto Speed' which allows you to set this speed. It has to be fixed as there is nothing in the synta protocol which allows goto speed to be changed by EQMOD.

As for the fault pin, don't worry, it is fine being connected to +5V. The A4988 boards use that pin for their 5V logic supply, but the DRV8825 boards don't need it, so Pololu decided to use that pin as a fault indicator instead. The way they designed the circuit though, there is a resistor in series with it on the driver boards which makes it safe to connect 5V meaning they remain compatible with A4988 boards. It is also perfectly fine to leave it disconnected.

Quote from the Pololu website:
Quote
Note that the carrier includes a 1.5k protection resistor in series with the FAULT pin that makes it is safe to connect this pin directly to a logic voltage supply, as might happen if you use this board in a system designed for the pin-compatible A4988 carrier

« Last Edit: January 11, 2015, 21:44:37 by TCWORLD »
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Tom Carpenter (AstroEQ)