[TriEmbed] Pinewood derby help

[Craig Cook]

Sounds good.  I'll order some of those.
For a diode, I have 10 of these 1N4001.  Would that work?
I also have 10 zenner diodes, BZX79-C3V3

Or, what do you recommend.  May as well add to my order.

Thanks
Craig

      From: Shane Trent <shanedtrent at gmail.com>
 To: Craig Cook <cncook001 at yahoo.com>; Carl Nobile <carl.nobile at gmail.com> 
Cc: TriEmbed <triembed at triembed.org>
 Sent: Sunday, January 8, 2017 3:25 PM
 Subject: Re: [TriEmbed] Pinewood derby help
   
Craig,
I would recommend a transistor with a lower gate threshold voltage. The transistor below is under $1, has a low Vgs threshold and a low Rds. 
http://www.digikey.com/product-detail/en/infineon-technologies/IPP039N04LGXKSA1/IPP039N04LGXKSA1-ND/2081141
Just make sure that the diode is reversed biased, cathode (stripe) connected to +5V. The closer you can get to putting the diode across the back of the motor the better. Across the leads going to the motor is a good second choice.
I think you have the concept down.
Shane



On Sun, Jan 8, 2017 at 3:01 PM Craig Cook <cncook001 at yahoo.com> wrote:

I think you are saying if I replace the IRF510 MOSFET with one of these:


FQP30N06 N-Channel NPN MOSFET


I could remove the 2N3904 from the circuit.


But, I also need a diode to sit between the +V and the load, which in my case is the motor.

Then I would have something like this:

CHIP -> 1k resistor -> gate on the FQP30N06

I would have external power (probably 5V) -> diode -> motor -> Drain on FQP30N06

When the CHIP sends the signal to the Gate it opens the circuit and the motor turns on.

Thanks

Craig


________________________________
From: Shane Trent <shanedtrent at gmail.com>
To: Craig Cook <cncook001 at yahoo.com>; Carl Nobile <carl.nobile at gmail.com>
Cc: TriEmbed <triembed at triembed.org>
Sent: Sunday, January 8, 2017 1:45 PM
Subject: Re: [TriEmbed] Pinewood derby help



Craig,

That circuit looks a little wonky. It seems they want to use the 2N3904 for voltage translation (the FET is not logic level sensitive, it is famous because you could buy it at Radio Shack) but they do not provide a ground reference for the emitter of the 2N3904, the emitter only connects to the FET's gate.

The BJT would turn on when the gate voltage (through the 4.7k resistor) reaches around 0.6V above the emitter voltage but the emitter voltage is floating with no ground reference. So if the circuit did turn on, it would pull the FET gate voltage up and turn on the FET. Turning off the FET has it's own issues though since there is no path to drain current from the FET gate, the FET will turn off in the semi random time it takes for the gate charge to leak away. You could make it work by putting a large resistor between the FET gate and GND but the FET would turn on faster than it would turn off.

It would be much more effective if you could use a more sensitive FET that could be driven directly from the logic pin (via a 1k or so resistor). This would let you drive current to turn on the FET as well as sink current to turn off the FET.

Note they are also missing a kickback diode across the load so you would be dumping nasty high frequency, high voltage spikes back into the power rail and eventually your chips will start acting oddly before dying. Do not skip the kickback diode, the body diode of the MOSFET does nothing to help tame the inductive kick when the FET is switched off.

Shane

On Sun, Jan 8, 2017 at 12:20 PM Craig Cook via TriEmbed <triembed at triembed.org> wrote:

Ah, learning more.  This is the project I am looking at:
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>https://chip.hackster.io/user024507/motor-on-9c6bd1?ref=channel&ref_id=5276_trending___&offset=22
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>Is the 2N3904 working as an isolator?
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>The donor truck contains these:
>BR8550D 064 (x 4)
>C1815Y 5L
>Super Chip STRX3A, 60100395
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>Could I reuse the C1815Y for my isolator?
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>I also have these new PN2222ABU, BC547B, P2N2222AG
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>I could attach a picture of donor truck board, but it would have to be less than 100k.
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>Thanks
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>Craig
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>________________________________
> From: Carl Nobile <carl.nobile at gmail.com>
>To: Craig Cook <cncook001 at yahoo.com>
>Cc: TriEmbed <triembed at triembed.org>
>
>Sent: Sunday, January 8, 2017 11:10 AM
>
>Subject: Re: [TriEmbed] Pinewood derby help
>
>
>
>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
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>Triangle, NC Embedded Computing mailing list
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>



   
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