[TriEmbed] Pinewood derby help

[Shane Trent]

Craig,

As long as you use a snubber diode across the motor's power terminals and a
cap near your microcontroller power pins, you should not need an
opto-isolator. As long as you match the N-FET's gate voltage sensitivity
with your logic voltage, you should be able to drive the FET's gate
directly via resistor (1k?) connected to a logic output. Drive the logic
output low during the low periods to turn the FET off rather than let the
gate float during the OFF period (float would turn-off a BJT but not a
FET). You could just add a large value (50k?) pull-down to the FET gate but
this would give you an asymmetry in the turn-on and turn-off times that
could make it hard to effectively use the full range of your PWM output.

Shane

On Sun, Jan 8, 2017 at 11:11 AM Carl Nobile via TriEmbed <
triembed at triembed.org> wrote:

> Yes, you will need something like a MOSFET to handle the higher current
> that the motor will draw and a different power souce that what is being
> used for the CHIP, but that won't isolate the motor from the electronics.
> You will still need an opto isolator.
>
> ~Carl
>
>
> On Sun, Jan 8, 2017 at 8:34 AM, Craig Cook <cncook001 at yahoo.com> wrote:
>
> Ah, that probably explains another project I saw.  It had a CHIP, motor
> and IRF510N MOSFET.
>
> I have some MOSFET's on order.  I'll wait for them and then try to drive
> my motor.
>
> Oh, exactly what Pete just said.
>
> Thanks
>
> Craig
>
> ------------------------------
> *From:* Carl Nobile <carl.nobile at gmail.com>
> *To:* Craig Cook <cncook001 at yahoo.com>
> *Cc:* TriEmbed <triembed at triembed.org>
> *Sent:* Saturday, January 7, 2017 10:35 PM
> *Subject:* Re: [TriEmbed] Pinewood derby help
>
> Craig,
>
> You'll need some sort of optical isolator between the motor and any
> electronics or the reverse EMF from the motor will fry the electronics.
>
> It's late as I send this, so I won't go into detail. Google it.
>
> Carl
>
>
>
> On Jan 7, 2017 9:38 PM, "Craig Cook via TriEmbed" <triembed at triembed.org>
> wrote:
>
> At my cub pack we have a "Dad's race" the night before the boys race.
> Dads don't have to comply to the same rules the boys do.  i.e. if we can
> get a motor on the car and it weighs more than 5oz, thats fine.  Purely for
> engineering fun.
>
> I have a donor RC dump truck I am going to take the motor and axel out
> of.  I have a NTC CHIP I was going to strap on to control the motor.
>
> I've got the kernel upgraded to 4.4 and PWM working.
>
> Am I correct in thinking if I can hook up the motor to the CHIP board I
> could use PWM to "slow" it down? i.e. if I let the motor spin at full speed
> the derby car wheels may just sit and spin.  If I can send the right amount
> of pulses I should be able to control the motor speed.
>
> The dump truck was powered by 3 x AA batteries, which makes me believe the
> motor accepts 5V or less, so using the CHIP should not fry it.  The motor
> has a 1 ohm resistor attached and a capacitor with 104 written on it.
>
> I'm ready to attach the motor to the CHIP, any reason I shouldn't and see
> what happens?
>
> Thanks
>
> Craig
>
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> --
>
> -------------------------------------------------------------------------------
> Carl J. Nobile (Software Engineer)
> carl.nobile at gmail.com
>
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