MD30C - sinking PWM control?

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MD30C - sinking PWM control?

Postby Bikey » Thu Oct 01, 2015 9:37 am

Hello - I am interested in using the MD30c as a fuel pump controller for a car. The engine control unit can output a PWM signal, but it is a negative signal. Is this compatible with the MD30C if I hook up the PWM to the ground (Input Pin 1 on the header that takes the PWM input) and feed the "PWM" pin (Input Pin 2 on the same header) a constant 5V?
Also - is it necessary to feed a signal to the DIR pin? If not, what direction is the default?

Thanks.
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Re: MD30C - sinking PWM control?

Postby waiweng83 » Thu Oct 01, 2015 2:16 pm

Bikey wrote:The engine control unit can output a PWM signal, but it is a negative signal. Is this compatible with the MD30C if I hook up the PWM to the ground (Input Pin 1 on the header that takes the PWM input) and feed the "PWM" pin (Input Pin 2 on the same header) a constant 5V?


Hi, may I know what did you mean with negative PWM signal? Does it mean the voltage is negative or just the polarity is inverted (0 = ON, 1 = OFF).
If it's just the polarity is inverted, you can make a simple NOT gate with a transistor in between the output of the ECU and the PWM input to the MD30C.
If the voltage is negative voltage, then the MD30C is not compatible because the GND pin at the input side is connected to the negative terminal of the battery internally.

Bikey wrote:Also - is it necessary to feed a signal to the DIR pin? If not, what direction is the default?


It's recommended to connect the DIR pin to GND if it's not used. The direction will be high on terminal A and low on terminal B.
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Re: MD30C - sinking PWM control?

Postby Bikey » Tue Oct 27, 2015 12:54 am

Thanks!
The PWM signal acts on the ground - so the ground wire of a setup is pulsed per the PWM frequency and duty cycle. For example, if hooking up my setup to a light in a car, the power signal would come from the car's battery and the ground would be hooked up to the engine control unit, which will pulse the ground circuit to dim the light.
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Re: MD30C - sinking PWM control?

Postby Bikey » Tue Oct 27, 2015 5:44 am

I should be able to use a pull up resistor on my PWM output, so that the PWM signal will be 5V when "off" and 0v when "on," correct?
Right now, the signal pulses between "on" and "open."
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Re: MD30C - sinking PWM control?

Postby waiweng83 » Wed Oct 28, 2015 10:38 am

Bikey wrote:I should be able to use a pull up resistor on my PWM output, so that the PWM signal will be 5V when "off" and 0v when "on," correct?
Right now, the signal pulses between "on" and "open."


Yup, you can do that.
You can also add a transistor to invert the polarity of the PWM signal.
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Re: MD30C - sinking PWM control?

Postby Bikey » Wed Nov 11, 2015 8:41 am

And one other question, for a different application, is there a suggestion ohm range for using a potentiometer to control speed? It looks like there is a figure specified in the manual for using a PWM pot (5k to 10k) - does the same apply to an external speed pot used to control speed?

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Re: MD30C - sinking PWM control?

Postby waiweng83 » Wed Nov 18, 2015 4:36 pm

Yup, the external potentiometer must be in the range of 5K to 10K.
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