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Conehead
01-19-2009, 07:37 AM
Hello all,

I have just finished verifying a Propeller based board that I designed to control 3 load frames.

It has:

1. 3 24 bit A/Ds, each with 4 differential or 8 single ended channels or a mix of diff/single-ended.· I used the ADS1256 from TI.· Good chip, but a bear to get the timing right.
2.·9 FET driven outputs from the Prop·to control 3 stepper motors.
3. 1 FTDI232R for connecting to the PC.
4. A PIC18F2221 connected to 15 inputs and 3 FET driven outputs for GPIO.
5. A whole bunch of ESD circuitry.

Each A/D and the PIC have their own SPI bus running to their own dedicated cog in the Prop.· Each motor is being run by their own cog as well, leaving me with one more to communicate with the PC.· However, I designed the board so that communications to the PC can run to either the PIC or the Prop (I am much better at writing PICBASIC PRO than SPIN or Assembler).· The PIC was originally added because I ran out of IO on the Prop.· I could have used a single SPI bus for the A/Ds which would have freed up enough IO, but I wanted them to run in parallel because of possibly long sample times.

I have created an assembler object (my first one...not just for the Prop) to run the A/Ds.· Once I have that polished, I will post it in the object exchange along with the portion of the schematic from the A/D to the Prop.

Still have a lot of programming to do for the steppers and the PIC/Prop comms, which I won't post because it is very application specific.

Mark Swann
01-19-2009, 10:10 AM
Looks great. http://forums.parallax.com/images/smilies/cool.gif

That's a busy board. http://forums.parallax.com/images/smilies/shocked.gif

hinv
02-03-2009, 12:20 PM
That looks like a nice clean board.

I am curious, what FETs did you use, what are the loads, and how did you connect them to the propeller. I am just learning about FETs and their capabilities, so am lookin for good examples of how to interface them to the propeller.

Thanks,
Doug

Leon
02-03-2009, 05:35 PM
The easiest way to interface MOSFETs is to use a driver like the Micrel MIC4426. They are widely available.

Leon

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Amateur radio callsign: G1HSM
Suzuki SV1000S motorcycle

Cluso99
02-03-2009, 06:01 PM
Nice board. Thanks for showing us. http://forums.parallax.com/images/smilies/smile.gif

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Links to other interesting threads:

· Prop Tools under Development or Completed (Index) (http://forums.parallax.com/showthread.php?p=753439)
· Emulators (Micros eg Altair, and Terminals eg VT100) - index (http://forums.parallax.com/showthread.php?p=778427)
· Search the Propeller forums (via Google) (http://search.parallax.com/search?site=parallax&client=parallax&output=xml_no_dtd&proxystylesheet=parallax&proxycustom=<HOME/>&ie=&oe=&lr=)

My cruising website is: ·www.bluemagic.biz (http://www.bluemagic.biz)

Timothy D. Swieter
02-04-2009, 06:54 AM
Nice setup Conehead.

Leon, what is the advantages of using a driver like you mentioned over connecting the MOSFET to the I/O?

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Timothy D. Swieter, E.I.
www.brilldea.com (http://www.brilldea.com) - Prop Blade, LED Painter, RGB LEDs, uOLED-IOC, eProto for SunSPOT, BitScope
www.tdswieter.com (http://www.tdswieter.com)

Bob Lawrence (VE1RLL)
02-04-2009, 07:40 AM
Leon said...
The easiest way to interface MOSFETs is to use a driver like the Micrel MIC4426. They are widely available.

Overview form the data sheet:

General Description Features

The MIC4426/4427/4428 family are highly-reliable dual low-side MOSFET drivers fabricated on a BiCMOS/DMOS process for low power consumption and high efficiency. These drivers translate TTL or CMOS input logic levels to output voltage levels that swing within 25mV of the positive supply or ground. Comparable bipolar devices are capable of swinging only to within 1V of the supply. The MIC4426/7/8 is available in three configurations: dual inverting, dual noninverting, and one inverting plus one noninverting output.

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Aka: CosmicBob

Timothy D. Swieter
02-04-2009, 08:09 AM
Thanks Bob, I did look at the data sheet, but I think I am missing some key point. Why is it better to swing closer to the supply rail and switch that voltage instead a logic level voltage? is it that the logic voltage doesn't full saturate (turn on) the MOSFET?

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Timothy D. Swieter, E.I.
www.brilldea.com (http://www.brilldea.com) - Prop Blade, LED Painter, RGB LEDs, uOLED-IOC, eProto for SunSPOT, BitScope
www.tdswieter.com (http://www.tdswieter.com)