Ouput pin drive capability ?

[John Chris]

Hi there, I'm working with the 28X2, and a BLDC motor with a low-level directional control lead. The stated input resistance for the motor direction lead is 10 kOhms, should I have any difficulty bringing this high with a Port B I/O pin.

I send the pin high, and it remains so for less than a second or so, and goes low. The motor direction is consistent with the state of the pin - turns as it should for a high, and then switches direction. This happens reproducibly. I've tried it on two separate Port B pins.

Thanks, Chris

 

[eclectic]

Chris.

Please post your circuit and program.

e

 

[Andrew Cowan]

I've never heard of a BLDC motor with a low level direction connection. Can you post the link to the motor?

 

[John Chris]

I have not drawn the circuit on paper, I could post gerber files, I suppose. I will post my program tomorrow, I really should investigate a little further. I just fired off the previous question hoping it was a short answer.

Thanks,

Chris

http://www.premotec.com/brushless.htm

 

[premelec]

with a 10K load at 5v out that's .5 ma - 40x less than the PICAXE's pin drive capability - that's assuming that the motor control works ok with 5volts...

 

[SAborn]

Sounds like the motor needs a high signal for one direction and a low signal for the reverse direction.
Might be why it starts one way and then reverses when your signal goes low.

 

[MartinM57]

that's assuming that the motor control works ok with 5volts...

...and that your power supply (what sort?) can keep up with the demands of the motor and continue to power the PICAXE

Flash a LED or put a SERTXD at the start of your program to see if it is the PICAXE resetting...and post your circuit...

 

[Dippy]

Are you using some kind of controller for the BLDC motor?

BLDCs normally have quite a few wires and you would have to do some rapid control via drivers, the complexity depends on the motor.

For accurate and up to date electrical specs ALWAYS get the nitty-gritty PIC datasheet from Microchip.

 

[BeanieBots]

My thoughts too.
It's unlikely that you could ever control a BLDC motor direct and reference to the 10k direction control implies a controller.
So, rather than have us all guessing what you might have, please give more details.

 

[Dippy]

But, in the event of no info and you say the input impedance of the control line is 10k (and assuming it's running at an acceptable logic level) then, yes, sounds fine.

Caveat: crystal ball getting a bit cloudy.

 

[westaust55]

Ouput pin drive capability

Hi there, I'm working with the 28X2, and a BLDC motor with a low-level directional control lead. The stated input resistance for the motor direction lead is 10 kOhms, should I have any difficulty bringing this high with a Port B I/O pin.

@Chris,

with respect to your post title,

In the PICAXE manual 1 on page 13 you will find a list of PIC types used for the various PICAXE chips. From there you can visit the microchip website and download the relevant PIC datasheet to determine to output capabilities.

OR

you can look at PICAXE manual 1 page 7 where Rev Ed kindly provide the recommended maximum current for a single output pin and a guide to the max loading for the entire PICAXE chip

 

[westaust55]

I have not drawn the circuit on paper, I could post gerber files, I suppose. I will post my program tomorrow, I really should investigate a little further. I just fired off the previous question hoping it was a short answer.

Thanks,

Chris

http://www.premotec.com/brushless.htm

Please indicate exactly which PREMOTEC motor that you are using. Nominally theya re all 12 to 24V on the link you give.

There is a 1Watt 4 wire motor than seemingly can operate at down to 4V which has 39 ohm windings

and a 2 wire motor but that only operates at down to 10V with a current of approx 1 amps.

But did not readily spot the one you are describing.

 

[John Chris]

Thanks very much for all the info / suggestions.

Briefly, before I review and post my circuit, the BLDC (Premotec BL58) possesses integral control circuitry. The pin assignment is something like:

1 - 24 V
2 - analog in (speed)
3 - frequency generator out (tachometer)
4 - CW / CCW (direction)
5 - GND

I am using separate power supplies for the motor and the 28X2. More soon. I appreciate the help, thanks.

Chris

 

[hippy]

I send the pin high, and it remains so for less than a second or so, and goes low. The motor direction is consistent with the state of the pin - turns as it should for a high, and then switches direction. This happens reproducibly. I've tried it on two separate Port B pins.

This is presumably to the CW/CCW control line. I'm not sure what you are describing here as you seems to suggest it goes one way when the line is high and the other way when the line is low. That seems to be correct operation.

Or are you saying the output pin drops low when it should not ?

You may have to post your code so we can see what you are doing but it could be something to do with the motor starting up and causing the PICAXE to reset. Have you looked at the output line without the motor connected using a LED+_R, multimeter or scope to check what it's level is.

Unfortunately it's not clear at present what the fault actually is which you are describing. A better description of what you do, what happens, and what should have happened, may clarify that.

 

[John Chris]

Reviewed my program ... a sily mistake on my part. I take some consolation in the fact that I may have introduced a few to a useful motor. Thanks for the suggestions / assistance.

Chris