keiner1234
Posts: 7
Joined: Mon Feb 25, 2013 8:52 pm

more tan one power and ground pin nessesery?

Thu Oct 17, 2013 11:45 pm

Hi,
i power 3 stepper driver with the raspi. i want to use fever cables so i was wondering if i can use one 3.3V and one gnd pin for all three. if not, can i connect both 3.3v pins and two gnd pins to power the driver?

thx

ame
Posts: 3172
Joined: Sat Aug 18, 2012 1:21 am
Location: Korea

Re: more tan one power and ground pin nessesery?

Fri Oct 18, 2013 1:20 am

You should probably have a second power supply for your stepper motors.

But, if your thing is working right now then don't remove any wires.

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joan
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Location: UK

Re: more tan one power and ground pin nessesery?

Fri Oct 18, 2013 8:08 am

Could you post a schematic of your current set-up? It's unlikely that you are powering stepper motors from the Pi's 3V supply.

keiner1234
Posts: 7
Joined: Mon Feb 25, 2013 8:52 pm

Re: more tan one power and ground pin nessesery?

Fri Oct 18, 2013 12:36 pm

off course i don't drive the stepper with the pi :)
i power the stepper driver (drvdrv8825)
Image

i hooked "reset" and "sleep" to 3.3V pins, "gnd" to a gnd pins and "step" and "dir" to gpio's.

right now i use one 3.3pin for two drivers and the other one for the last driver. But i would prefer to use only one 3.3pin and one gnd-pin for all three drivers if it would run too.

(motor power supply is of ccourse an external power supply)

ame
Posts: 3172
Joined: Sat Aug 18, 2012 1:21 am
Location: Korea

Re: more tan one power and ground pin nessesery?

Fri Oct 18, 2013 1:20 pm

Are you using a breadboard, or are you soldering the wires to the stepper driver boards? Just curious.

Yes, you should be able to use one 3V3 line and one GND line. Let's call the boards A, B and C. On each driver board you can connect ~RESET and ~SLEEP together, then you can "daisy chain" the three boards. One wire from 3V3 on the Pi to board A (~RESET and ~SLEEP together), then a wire from A to B (~RESET and ~SLEEP together), then a wire from B to C (~RESET and ~SLEEP together). The same for GND. One wire from the Pi GND to A GND, then A GND to B GND, and B GND to C GND.

keiner1234
Posts: 7
Joined: Mon Feb 25, 2013 8:52 pm

Re: more tan one power and ground pin nessesery?

Fri Oct 18, 2013 1:45 pm

Thank you, thats what i wanted to know.
The driver comes with a pinheader, so i just use jumper wires to connect them. But since i had only two 3.3v pins, i made a T-Wire with three pins on itself, so i can use my female jumperwires to have a female T-Wire without cutting my jumperwires.

But i wanted to solder the Stepper drivers on an pcb so it's less of a mess. also i can solder in bridges so i can esaly change the step size without using new wires.

karlkiste
Posts: 189
Joined: Tue Jan 22, 2013 8:50 am
Location: berlin, germany

Re: more tan one power and ground pin nessesery?

Fri Oct 18, 2013 2:39 pm

You can only draw little current (I think it's rated 50mA) from the 3.3V pins together. That little current can easily go through one pin.

I've been powering a Model B pi with camera "backwards" through one 5V and one ground pin from the GPIO header. While this is really not recommended (for bypassing fuses and such...) it worked without problems. I'd say, 1A per pin is OK for the pin itself. I can't say anything about the copper traces, as they're hidden inside. GPIOs, not to forget, are allowed maximum 16mA per pin.

keiner1234
Posts: 7
Joined: Mon Feb 25, 2013 8:52 pm

Re: more tan one power and ground pin nessesery?

Fri Oct 18, 2013 3:15 pm

You can only draw little current (I think it's rated 50mA) from the 3.3V pins together.
But can i also draw 50mA from one pin an leave the other one untouched?

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